L12L07 Handout

LS12L07 - Autodesk Revit and 3ds Max Design for Lighting and Daylighting simulation

Session Type: Seminar

Session Day/Time: Monday, May 7th, 2012, 9:00 AM -5:00 PM

Session Number: L12L07

Speaker: Pierre-Felix Breton, Autodesk Media & Entertainment

Class Audience

Autodesk 3ds Max users and Revit users who want to bring Revit models into 3ds Max for rendering or animation

Class Description

This session will provide an overview of the tools available to you in the Autodesk products family for exploring, defining and validating lighting projects.

Focused on the interoperability of Revit and 3ds Max design, you will learn what is possible to achieve with Autodesk Revit and 3ds Max Design for electrical lighting design as well as daylighting design.

An overview of the rendering capabilities or mental ray and iray will be provided as well as production oriented strategies to integrate lighting photometry and solar information for lighting studies.

Tips and tricks will be provided to support project workflows where the design elements are changing and evolving on a regular basis.

Learning Objectives

1. Get a general overview of BIM technologies applicable to lighting design projects. 2. Learn about interoperability strategies to adopt when translating data from one software to another. 3. Learn about capabilities and limitations of lighting simulation technologies: what are the pitfalls of lighting

simulation? 4. See production examples used in the context of real projects.

About the Speaker

Pierre-Felix Breton is a software designer who specializes in the field of physically-based lighting simulation and rendering. Currently employed by Autodesk Media & Entertainment, he participates in the creation of products such as Autodesk® 3ds Max®.

He also contributes to the design and development of materials and shader libraries included in Autodesk products where color consistency and physical accuracy is critical.

As his professional background includes electrical engineering, computer programming, and theatrical lighting, Pierre-Felix consults regularly on various architectural lighting design projects as a designer, technical coordinator, and simulation specialist.

Autodesk Revit and 3ds Max Design for Lighting and Daylighting simulation

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Contents

Revit and Lighting ................................................................................................................................................................... 4

Revit Architecture or MEP? ................................................................................................................................................. 5

Daylighting and Revit ........................................................................................................................................................... 5

Electrical Lighting in Revit (Light Fixtures) ........................................................................................................................ 11

Lighting Calculation Options .............................................................................................................................................. 23

Interoperability strategies between Revit and 3ds Max ........................................................................................................ 24

DWG vs FBX ..................................................................................................................................................................... 25

Strategies to adopt with Revit Views ................................................................................................................................. 32

Modeling with 3ds Max in mind ......................................................................................................................................... 36

More Tips and Tricks ......................................................................................................................................................... 42

Helpful scripts to help working with Revit Data ................................................................................................................. 45

3ds Max Rendering at a Glance............................................................................................................................................ 49

Rendering in 3ds Max Basics ............................................................................................................................................ 50

Simplified mental ray render panel .................................................................................................................................... 56

Exterior Day-time Rendering ............................................................................................................................................. 56

Interior Day-time Rendering .............................................................................................................................................. 61

Fine Tuning Indirect lighting .............................................................................................................................................. 69

Non-Photo Real Renderings (NPR) .................................................................................................................................. 73

Lighting Analysis in 3ds Max Design .................................................................................................................................... 75

What daylighting metrics do I want to calculate? .............................................................................................................. 76

Is the simulation tool capable of reliably calculating these metrics? ................................................................................. 76

The lighting analysis workflow ........................................................................................................................................... 77

Report Light Levels ............................................................................................................................................................ 86

Daylighting Metrics ............................................................................................................................................................ 94

Materials and Finishes for Lighting Analysis ................................................................................................................... 101


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Glass and Glazing for Lighting Analysis .......................................................................................................................... 106

Color Management Techniques .......................................................................................................................................... 110

Basics of color management ........................................................................................................................................... 111

The “Linear Workflow” - Color management applied to rendering .................................................................................. 116

HDR Imaging ....................................................................................................................................................................... 121

Using High Dynamic Range (HDR) images as backgrounds images ............................................................................. 122

Compositing with HDR images. ....................................................................................................................................... 130


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Revit and Lighting This section demonstrates the basics of creating a light fixture family. Autodesk provides a tutorial entitled “Revit Families Guide” (just Google for it). I highly recommend that you take the time to go through this tutorial.

Modeled in Revit, rendered in 3ds Max © Pierre-Félix Breton 2012


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Revit Architecture or MEP?

Don`t bother. Revit 2013 combines all those disciplines into single software.

Daylighting and Revit

Revit has useful (but limited) abilities to perform shadow studies. In Revit, you can perform the following tasks:

Inspect shadows from the Sun in real time in the 3D environment, for outdoor and indoor situations.

Perform an animation of the Sun over the course of a day or a year.

Save presets for the date and time (winter, summer etc.)

However, keep in mind that Revit also has the following limitations:

Revit do not handle quantification of light (unless using an add-on pack, which is also limited to exterior lighting).

Revit do not perform calculation from the skydome (unless using the rendering functionality)

Revit do not handle daylight savings time switching automatically: you must remember to change this setting each time you change the date.

Site location / Coordinates

Per View Sun settings

In Revit, Sun Settings are view based. That is, each view can have its own Sun Settings. This also gets exported to 3ds max via FBX.

The Sun Path tool of Revit has useful (but limited) abilities to perform shadow studies. In Revit, you can perform the following tasks:

Inspect shadows from the Sun in real time in the 3D environment, for outdoor and indoor situations.

Perform an animation of the Sun over the course of a day or a year.

Save presets for the date and time (winter, summer etc.)

However, keep in mind that Revit also has the following limitations:

Revit do not handle quantification of light (unless using an add-on pack, which is also limited to exterior lighting).

Revit do not perform calculation from the sky dome (unless using the rendering functionality)


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The Sun settings are available in the lower part of the Revit interface. Each view can have its own Sun Settings.


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Project Location

Revit uses Google Map services to let you find the exact project location. This also feeds in the algorithms used to calculate the Sun angle.

The Project Location will translate to 3ds Max via FBX.

Note that the Use Daylight Savings time is in my opinion misplaced. You need to keep that in mind when doing shadow studies.


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Defining the North offset

Defining the North direction is a bit tricky. You need to be in a Plan view where the project base point is displayed. You then manipulate the project base point to define the north direction offset. Obviously, it is easier to do when the Sun Path widget is also visible in the View.

In the Visibility Graphics dialog of the View, make sure that “Project Base Point” from the “Site” category is set to be visible.

A blue circle with a cross should be visible. This is the origin of the Revit model.

Select and in-place edit the angle from True North

The north direction is now correctly oriented in relation to your model.


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Enabling shadow studies

Shadow studies can be done in any 2D or 3D view.


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Exporting to Ecotect for shadow ranges

Ecotect has a lot of functionality around lighting simulation and environmental simulations. One of them is the “shadow ranges” built for understanding the shadow of a building on an entire day at once. This is useful for a variety of applications such as:

Optimizing the placement of solar panels

Optimizing the placement of landscaping elements (pools, rest areas etc.)

Comparing shadow impacts of different roof configurations

Etc.

Two types of roofs compared in Ecotect for a private house, allowing understanding the ideal placement of landscaping elements such as pool, deck etc.


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Electrical Lighting in Revit (Light Fixtures)

Modeling a light fixture

When making new families, start with a template: the basics are usually already in place to get you started.

Revit family templates usually define origin with dedicated intersecting reference planes. Use them as your starting point.


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Always start by drawing reference planes corresponding to key boundaries of the light fixture you are modeling.

You will use those reference planes to align geometry later on.

Reference planes should be set on the side as well. They will become helpful to constrain extrusions drawn in a next step.

The finished geometry and light source aligned just below the luminous aperture.

The luminaire is drawn in 3D with a combination of extruded solid (blue) and extruded void (orange)


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Light fixture family inserted in the model.

Note: by default, most Revit views do not display light source icons.

Turn them on in the visibility graphics override of your View. However, they generally do not display very well in shaded views (they are rendered as if they were solid entities)


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Recessed lights cuts the ceiling

If you insert recessed fixtures in your model, I recommend using a void to appropriately cut the ceilings when they are inserted.

Recessed fixture need to cut holes in ceilings to look right in renderings.

A void object in the family solves the issue. The Cut tool will let you cut the ceiling.


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Parametric geometry for light fixtures

Some manufacturers provide RVT families that are the result of bulk imports of existing CAD data. As a result, parts are fixed, models are not parametric and levels of details are not considered. This method sort of negates the idea of BIM.

Left: A decorative light fixture imported as a single object in Revit does not allow benefiting from parametric feature such as cable length or level of detail.

Right: The same fixture has been made parametric: parts can be hidden or displayed based on the level of detail of the view and suspension cables can be stretched independently.

Parametric Cable stretching based on the distance between tow reference planes.


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A recessed light fixture made parametric offering a range of 1 to nth luminous heads.


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Recessed fixture with a tilt angle parameter implies nesting families inside each other.

Materials and finishes

Part of the BIM process implies that families are not set to default materials and finishes. A bonus is that if this is done properly, the rendering in 3ds Max is only made easier. © Pierre-Félix Breton 2012


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Level of Detail Considerations

When it is “good enough”

Typically, manufacturers will provide detailed 2D profiles and drawings for their products. Here is an example I got from a window manufacturer:

Detailed profile for an aluminum window: too much detail to use in 3D.

In no way I would want to use this “as-is” to create 3D extrusions: the Revit display would quickly get on its knees. Instead, the idea is to model a “rough” version of the original shape, where for example, rounded corners become sharp and dents and details become straight.

Simplified sweep profile matching closely the original shape, still making an acceptable 3D window.


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Built-in Detail Levels

You are certainly well aware of the built-in Level of Detail functionality that you hook up in the Family Editor to determine when an object is visible or not:

Connecting the Visibility of an object to the Detail Level of a View

A family displaying less/more detail based on the Detail Level of a View

Along the same lines, it is a good idea to create families that will be repeated many times in a model (like a curtain wall mullion) taking advantage of this:


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More flexibility with “custom” Detail Levels

Here is an idea: what if you were able to create as many detail levels for your families? By leveraging the principles behind subcategories, you have total flexibility with the amount of details you can put in (or hide from) a view.

For example, I came across a file that was designed with a fair amount of details for office workstations:

Small details on chairs and cabinets created as extruded circles could be placed on their own subcategory

Unfortunately, those objects where all classified as “3D Elements” as subcategories. As a result, it’s an all or nothing situation for display and export to 3ds Max.

If those elements where assigned a different subcategory such as “3D Elements – Details”, we would be able to turn them off in our View or accelerate the File IO process with exporting to 3ds Max for example.


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Scheduling & Annotation

Light fixtures can be scheduled, annotated just like any other type of entities.

A light fixture schedule can contain numerous amounts of fields that you may have defined as parameters associated with the family.

They can be filtered by level, zone etc.

A view has been defined to draw light fixtures in red and halftone everything else.


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Tagging also extracts Meta data from the families.


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Lighting Calculation Options

Realistic Visual Style & Rendering

New in Revit 2013, if you use Realistic Visual Styles in 3d isometric or perspectives views, you can now specify artificial lights & Photographic Exposure lighting schemes, exactly the same way you do in the mental ray renderer.

Performance is slow, but for presentation graphics where you don’t want to render the image using mental ray, it’s a praiseworthy improvement

Eulum Tools

The calculations can be done within seconds once lighting fixture families and materials are validated for accurate lighting calculations. Multiple Rooms or Spaces can be computed at once and lighting results are evaluated using ElumTools interactive visualization UI. This all adds up to a tremendous amount of time saved integrating lighting with Revit.


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Interoperability strategies between Revit and 3ds Max

There are several things you can do directly in Revit to minimize the work required in 3ds Max prior to rendering or animating. This section focuses on methods that can be adopted in Revit to prepare a model for 3ds Max.


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DWG vs FBX

The general concept

Whether you use FBX or DWG, the same principles applies. In essence, Revit exports the content of a view into a file format which then get imported into 3ds Max.

Whether you bring data in 3ds Max via FBX or DWG, both offer methods to organize your data inside 3ds Max to avoid getting what we typically call a “polygon soup”.

Revit 3D View DWG File Link Manager

« Derive By » Filter

3ds Max Entities

Revit 3D View

FBX File Link Manager

« Combine By » Filter

3ds Max Entities


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Quick comparison between FBX and DWG file formats related to 3ds Max

Although FBX and DWG have a fair amount of distinct characteristics, let’s have a look at what is relevant for bringing Revit data into 3ds Max

FBX DWG Comments

Curved Geometry Fixed Tessellation Controlled tessellation via Solids

(More detailed information below)

Organization of data inside 3ds Max

Object Meta Data in Scene Explorer

Layers

Scene complexity management

Combine by Material Combine by Family Type Combine by Category Combine as One Object Do not Combine

Combine by Layer Combine by Color Combine as One Object Do not Combine

(More detailed information below)

Lines & Terrain Contours

No Yes

Materials Yes Yes (but names are messed up)

Lights Yes No

Daylight / Site Location Yes No

Unless specified otherwise, the rest of the document will assume that data is brought to 3ds Max via the FBX file format.


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“Combine by” filters overview

Typically, 3ds Max has hard time dealing with thousands of individual objects. In fact, 3ds Max deals better with fewer objects, with more polygons into them.

In 3ds Max, the File Link Manager offers a few data organization tools that should not be neglected, which are not all available with regular import options. Among other things, the File Link Manager offers options to combine entities together, to reduce the number of objects in 3ds Max.

Therefore, I recommend exploiting one of the “Combine By” option that is available for both FBX and DWG files, via the File Link Manager.

“Combine by” filters available with DWG

Pros Cons Comments

By Layer, Keep Block Hierarchy

Preserve Materials ( but their names are lost)

Creates many Max objects, to support complex block structures (one per family)

Leverage the Layer Mapping capabilities with Subcategories (see below)

By Layer Reduce object count.

Materials are Lost

Creates many Max objects, to support complex block structures (one per family) due to a bug in this filter.


Families exported as blocks not exploded due to a bug in Max DwG importer

By Color Reduce object count. Materials are Lost

Creates many Max objects, to support complex block structures (one per family) due to a bug in this filter.


Families exported as blocks not exploded due to a bug in Max DwG importer

As One Object

--- Everything is in a “polygon soup”.

Can be slow to import/link

Creates a unique VIZBlock object which combines meshes and lines into a single object

Avoid this option on large Revit models


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By Entity Preserve each object individually selectable.

Increase object count in 3ds Max, reducing overall interactive performance.

Great for keeping furniture elements as individual elements.

“Combine by” filters available with FBX

Pros Cons Comments

By Material

Reduce object count.

Prevent Multi Sub Object Materials from being created.

You depend on the granularity of the material assignments in Revit. For example, if all curtain walls use the same glass material as interior doors, they will be combined in the same object in 3ds max.

Great method if you do not plan to move objects around and don’t want to deal with Multi Sub Object Materials

By Family Type

Reduce object count.

Prevent Multi Sub Object Materials from being created.

Multi Sub Object Materials are created.

Good balance between scene complexity and flexibility

Parts has problems

By Category

--- Multi Sub Object Materials are created.

All Walls are clustered together, all Roofs and so on…

Hmm, what where we thinking when we have implemented this one….?

Parts has problems

As One Object

A single Multi Sub Object Materials is created, which is simple to manage

Everything is in a “polygon soup”.

Can be slow to import/link

Great for quick lighting studies where you only care about massing

Do not Combine

Preserve each object individually selectable.

Increase object count in 3ds Max, reducing overall interactive performance.

Great for keeping furniture elements as individual elements.


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Curved objects from Revit to 3ds Max

The Revit database internally store entities in the form of “solids”. On the other hand, 3ds Max store entities in the form of faces (polygon meshes). Therefore, a tessellation (conversion) process has to occur somewhere in between.

You will notice below that the results of this tessellation are not quite the same depending on the file format you choose. Some work better than others. Hopefully, this will improve over time but for now, let’s state how things are:

The Revit viewport

The Revit camera triggers the level of detail for each object on the fly, based on the viewing distance. This dynamic tessellation system has 16 different levels, or steps. The following images illustrate what you can get in Revit when zooming closely on small, curved objects:

Small curved objects (a light fixture in this case) remain smooth in the Revit viewport.

The Revit renderer (mental ray)

When rendering using mental ray inside Revit, the same view dependent tessellation occurs. As a result, the rendered image receives the same polygonal information than the viewport and the results look consistent:

Revit Entity ("Solid")

View Dependent Polygonal

Tessellation Viewport


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\

Rendered in Revit, curved objects remain smooth

Revit FBX 3ds Max

Fixed tesselation

Although Revit has the capabilities to subdivide curved geometry with a high level of accuracy, the internals of Revit associated with geometry tessellation are fixed and unexposed to the users and/or the API in the moment.

Therefore, when exporting to 3ds Max via the FBX file format, the level of detail used by the Revit FBX exporter is using a fixed value. Unfortunately, you get what you get and some objects will appear too coarse, especially small tubular elements:

Exported in FBX and brought in 3ds Max, objects are tessellated with a fixed level of detail / resolution.

At this stage, you cannot increase the resolution of the objects anymore as everything is baked into polygons at the export from Revit stage.


View Dependent Polygonal

Tessellation

Renderer (mental ray)


Tessellation at fixed

resolution FBX file

3ds Max FBX importer /

File Link

3ds Max polygons


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Revit DWG 3ds Max

A potential solution to the tessellation problem

The DWG format offers and interesting option to preserve the quality of curved elements. By exporting to DWG as ACIS solids, we maintain the parametric curvature information in the DWG model. That is, we bypass the Revit tesselator.

The ACIS solids option from the DWG exporter will prevent entities from being tessellated as polygons by Revit. Solid information will be maintained.

Doing so gives us the option to use the 3ds Max tesselator available in the 3ds Max DWG import dialog, which offers control over mesh resolution for incoming solid entities:

We then rely on the 3ds Max DWG importer to do the tessellation, which is not View Dependent and not locked to a fixed value.


DWG file (exported with the ACIS solids

option)

3ds Max DWG importer

Tessellation from Solids to meshes at

Import Time 3ds Max polygons


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Strategies to adopt with Revit Views

Split your model across several views

Instead of making a general 3D view of the Revit model and exporting it to a giant DWG or FBX file, I recommend to split the model across several distinct views with the appropriate filters defined. The gain here is that you will reduce the overall complexity of the model (manage it into smaller chunks) and be able to use different “Combine By” options.

This strategy will let you, for example, combine all walls and ceilings “By Material” and leave Furniture or Cabinetry uncombined. To achieve this, you can leverage the Visibility Graphics Override and Filters.

Two views where only furniture and interior walls are visible.

3ds Max Exported

Views View Revit

BIM

Building Shell FBX Combine By

Material

Stairs FBX Combine By

Material

Floors & Ceilings

FBX Combine By Family Type

Furniture DWG By Layer


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Two views where only the exterior shell and internal structure are visible.

With this strategy, you gain control over how the data is organized into 3ds Max. Furthermore, you can envision using this approach to allow multiple 3ds Max users to collaborate on the same project:

Exported Files from

Views 3ds Max

Separate Max Files

Xrefed in 3ds Max

Final.Max

Building Shell.max

Combine By Material

FBX

Stairs Combine By

Material FBX

Floors & Ceilings

Combine By Family Type

FBX

Furniture By Layer DWG


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View Type & Project Structure Tip

To help with the above process, I like to identify views with special keywords. For example, assign a custom parameter to Views and mark them as “*Export to 3ds Max” as illustrated below:

A parameter named “View Type” applied to the View, with a custom property “*Export”…

Views with the same parameter “*Export” grouped together the Revit project browser

Parts & Views gotcha!

Risk of getting overlapping objects

Keep in mind that Parts are separate objects than their originating Revit entities. Therefore, be careful about the Parts Visibility option in the View, as you can end up with duplicated / overlapping objects in 3ds Max which will automatically lead to render artifacts.

Parts Visibility set to “Show Both” will create overlapping geometry in the DWG/FBX file and you will get rendering artifacts in 3ds Max.


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Problem with FBX Meta Data for Parts

Parts are a special “derived” object in Revit. As a result, their Type/Category is stored into a “Original Type/Category” field. This was not taken into account by the FBX importer of 3ds Max 2012. As a result, when you import Parts you will get something like this in the Scene Explorer of 3ds Max:

Parts in 3ds Max Scene Explorer: note how Category, Family and Types are all the same.

One major consequence with this problem is the fact that the Combine by Category or Combine by Family Type from the FBX File Link dialog will treat all Parts as belonging to the same Type/Category. As a result, they will all get combined together, regardless of their original Type/Category.

This is not a problem with Combine By Material or Do Not Combine options.

Partial scripted fix for Parts Meta data

If you used the “Do Not Combine” options from the File Link manager, you can still “fix” the Meta data issue with a scripted tool. This script is provided in the section entitled Fixing Parts Meta Data (below).

Since this script is fixing the Parts Meta data after the import/link process, it cannot be used to solve the Combine by problem discussed above.


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Modeling with 3ds Max in mind

Take advantage of subcategories with DWG export

Revit DWG Export supports Subcategories

The Revit DWG exporter allows customizing on which layer exported entities will land. Furthermore, you can also define this at the subcategory level. Therefore, you can then leverage this flexibility if you import data in 3ds Max via DWG.

In the family editor, try to classify objects by subcategories:

A window frame split into a Wood Frame Subcategory and a Cladding Subcategory

In the Revit DWG exporter, give those subcategories their own layer name:

The DWG exporter has been set to export those two Subcategories on dedicated AutoCAD layers.

In 3ds Max, the entities will land on the same layers:

Families end up being split across several layers, as specified in the DWG export dialog of Revit.


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Join geometry when possible

Joined geometry provides clean edges between intersecting objects. This also gives hints to the rendering engines of max, shaders and global illumination algorithms about where object “ends”.

Join geometry is a great preparation tool for making render friendly models

In Revit, the ceiling on the left is not joined with the walls. On the right they are joined together.

As a result, some rendering algorithms misses the edges that you are looking for in 3ds Max

If you intend to render in 3ds Max with contour shading you may want to consider getting clean, joined, geometry. The same goes for mental ray global illumination as it tend to leak light from outside. On the other hand, render engines like NVIDIA iray remains unaffected by geometry that is not joined.


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Dealing with overlapping geometry in 3ds Max

There are cases where objects overlap each other and you can’t fix it because they are tied into a workset that you can’t touch for any given reason. This is typical for Revit models that contain floor objects for finishes such as carpet on the same level as the concrete slab. Normally, an offset would need to be defined but this is often missed.

As a result, you get coplanar objects that produce display and render artifacts in 3ds Max:

Coplanar objects often show flickering effects like this in the display.

One quick method to “fix” the problem is to apply a Push modifier on the object, to push the polygons out slightly, just enough to resolve the problem about coplanar geometry. Perfect for carpets and other thin elements:

A Push modifier on the offending object will push the polygons out a bit, resolving the coplanar issuess


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Materials & Finishes

Paint materials on edges

Holes cut in walls will leave a default material assigned to the inner edges. This will be a problem inside 3ds Max, depending on the Combine by option you use with FBX.

Edges/Borders around windows are assigned to a default material.

I recommend using the Paint Material tool to apply a finish that matches what you want upfront, rather than waiting to fit it in 3ds Max:

Edges of walls painted with the appropriate Material in Revit


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Materials in Families

As we previously seen, a lot can be done in 3ds Max when family elements have been assigned to subcategories or materials. This is made possible by the different Combine By options that FBX and DWG importers of 3ds Max offer.

As a general strategy, I recommend to assign family components a dedicated material that will be retrieved later in 3ds Max. I suggest avoiding leaving them as “By Category” unless you adopted a workflow where each subcategory is properly defined.

Assign a dedicated material to all the components of a family, whether it is explicitly assigned to the object, or defined By Category/Subcategory

This is where adopting a naming convention becomes useful: it avoids confusion. It does not matter what convention you adopt, as long as you get “something”.

Revit 2012 material names will carry over 3ds Max via FBX

Cabinet

Casing

Panels Veneered Wood

Legs Chrome

Door

Panel Solid Wood

Handle Chrome


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Lights “glows” in 3ds Max

To prepare lights as glowing objects in 3ds Max, make a Glowing Material and apply it to a fake lamp surface with the Paint tool. This material will carry over FBX and appear as glowing in the final rendered image.

A glowing material applied in the family with the paint tool to a single surface.

The rendered image in 3ds Max, using NVIDIA iray renderer. © Pierre-Félix Breton 2012


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More Tips and Tricks

Nitrous display driver issue with DWG data imported in 3ds Max

3ds Max 2012 shipped with a new display driver called “Nitrous”. This is the default driver. Unfortunately, entities created by the DWG import plugin have a display bug with this driver and disappear.

There are two (2) solutions to this problem, which are explained below:

(1) Revert to the DirectX display driver

Reverting to the Direct X display driver is done from the Customize | Preferences… | Viewports dialog

(2) Apply an Edit Mesh modifier on VIZBlocks

VIZBlocks are unsupported by Nitrous in the moment, due to simple bugs. To work around this problem, apply an Edit Mesh modifier on them. This will “fool” the Nitrous display driver making it think that VIZBlocks are now regular Editable Mesh objects, and will display correctly in Nitrous

Note: I provide a script to automate this process in the section entitled Helpful scripts to help working with Revit Data below.


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Save render time by simplifying glazing

Glazing can be time consuming for ray tracers. One method to improve render times is to simplify glazing in a way that they have a single flat polygon instead of representing glass with thickness.

A curtain wall glazing panel is solid geometry

Delete polygons

The main idea is to delete 5 polygons out of 6 and leave only a thin surface. This is a achieved with an Edit Poly modifier.

The flattened glazing panel: use an Edit Poly modifier and delete the unwanted polygons.

Compensate the Glazing material

When a glazing pane has been turned into a flat polygon, you need to change its material to take it into consideration; otherwise ray tracing engines will get “confused” with refraction.


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An A&D Material set to Thin-Walled and an Autodesk Glazing Material set to use a single “Sheet of Glass”

Exporting multiple cameras from Revit

Don’t look for it; it’s not possible to export all Camera Views into a single FBX file in the moment. However, there is a workaround:

1. Make a Camera in Revit 2. In the Visibility Graphics/Override, turn off all objects 3. Export to FBX 4. The FBX file will contain only that camera….

Nothing prevents you from exporting a FBX file with no geometry in it… This is a quick way to get only a Camera in 3ds Max!


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Helpful scripts to help working with Revit Data

Note: The following scripts are provided as-is and are not supported or guaranteed by Autodesk. Be sure to back up you data prior to use them.

Fixing Nitrous display driver issues with DWG data imported in 3ds Max

Description

As previously discussed, the Nitrous display driver will not display VIZBlocks unless you apply a Mesh Select modifier on them.

Download

I wrote a script automating this process, download it here: http://bit.ly/slp7yh

Simply run the script on freshly imported data from AutoCAD. It will spot any VIZBlocks and apply a Mesh_Select modifier.

Create a Layer per Revit Category

Description

A script that loop through all objects and move them to a layer matching the Revit Category, by extracting meta information that FBX files exported from Revit carry over 3ds Max:

After running the script over a Revit model imported/linked with FBX data

It will leave untouched newly added objects and native 3ds Max objects (or anything missing this Meta data).

It will “fix” parts by assigning them to their Original Category Name, Family Name and Type Name so theiy also land on the appropriate layer.

http://bit.ly/slp7yh


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Limitations:

This script will not work when using Combine By Options that destroy meta data, such as Combine By Materials, As One Object or else.

If you run this script on an existing model from which you had cleaned up layers already, you may lose your original scene organization.

Download location

Download it from here: http://bit.ly/vp8miH

Scene Explorer Customization for Revit Data

Description

It is generally useful to list objects in the Scene Explorer with a bit more information that what is available out of the box. I am providing a script that will allow you to add extra columns in the Scene Explorer:

Material Name

Material Type

Object Plugin Type

Layer Name

Also, note that it does not save anything in the scene so it will not break file compatibility with other 3ds Max users who have not installed those scripts.

Download the script & install instructions

Download it from here: http://bit.ly/rA2GqM

The script has to be placed in the /scripts/startup/ folder of your 3ds Max installation as it needs to be treated as if it was a 3ds Max plugin:

http://bit.ly/vp8miH

http://bit.ly/rA2GqM


47

Extracting Revit parameters in 3ds Max

Revit parameters are stored in 3ds Max as “Custom Attributes” on objects and can be inspected with MAXScript. Here are a few examples:

Inspecting properties on the selected object:

-- script begin

(

objCustAttribs = custAttributes.get $ 1 baseobject:false –returns custom

attributes from the selected object

showproperties objCustAttribs – lists all custom attributes returned

)

–script end

Will return something like:

.Category_Name : string

.Family_Name : string

.Type_Name : string

.Keynote : string

.volume : string

.Area : string

.Manufacturer : string

.Comments : string

.Type_Comments : string

.description : string

.length : string

.Assembly_Code : string

.Cost : string

.Structural_Usage : string

.Top_Offset : string

.Base_Offset : string

.Base_Constraint : string

.Unconnected_Height : string

.Top_Constraint : string

.Room_Bounding : string

.width : string

.Location_Level : string

.Notes : string

.isUsedForMasonryCalculations : string

.isWindowOpening : string


48

Therefore, invoking:

$.Family_Name

Will return:

"Basic Wall"

Fixing Parts Meta Data

Description

The following example is used by the Create a Layer per Revit Category (see above) to restore Meta data into Parts which are imported without Categories, Family Names and Family Types.

--loop through all scene objects

for obj in Objects do

(

--get custom attributes from object,

--as Revit meta data is stored as such on objects in Max

local objCustAttribs = custAttributes.get obj 1 baseobject:false

--check if the object has custom attributes

if (objCustAttribs != undefined) do

(

--check if the object has a Type_name property,

--insuring that the object effectively comes from Revit via FBX

if (hasProperty objCustAttribs #Type_Name) do

(

-- Check if the #Type_Name is a Part

if ((getProperty obj #Type_Name) == "Part") do

(

--recopy all original properties into the real properties

--so the objects land on the right layers later in the same code / script

obj.Type_Name = obj.Original_Type

obj.Category_Name = obj.Original_Category

obj.Family_Name = obj.Original_Family

)--end if

)--end if

)--end if

)--end for loop

Download location

Download it from here: http://bit.ly/vp8miH

http://bit.ly/vp8miH


49

3ds Max Rendering at a Glance This section is intended for users of Autodesk® 3ds Max® Design* software (version 2010 or higher). The objective is to demystify mental ray® renderer rendering and present it in a simple way. The paper reviews common scenarios that architects, designers or engineers face when rendering with mental ray. It is targeted at users who have a good understanding of the 3ds Max Design interface and basic notions of rendering and photorealistic rendering workflows


50

Rendering in 3ds Max Basics

Materials

Recommended Material Types

The flexibility of mental ray and the evolution of 3ds Max and 3ds Max Design created some confusion around which material should be used with mental ray. Here is my advice: for 99% of the rendering workflows, you will want to use the A&D material.

The other materials will work, but the A&D material contains mental ray specific optimizations that will guarantee speed and quality over, for example, the traditional Standard material or the legacy Architectural material.

WallPaint, Wood, Concrete and Ceramic Materials at works. (Models: Maximilian Tarpini)

Where can I fix “missing files” messages?

If you open a 3ds Max file and you get an error message stating that some files are missing (textures, weather files, photometric files…), you can remap them to a valid path from the File | Asset Tracking dialog.

The Asset Tracking dialog of 3ds Max allows you to identify and repath externally referenced files from your scene.

Subtle reflections on Wall Paint automatically created by the Autodesk Wall Paint Material


51

Lights and Shadows

Units and Scale

Physically based lighting computation implies that light attenuates using the inverse square falloff law, which simply means the intensity of light declines exponentially with the distance it travels. Therefore, it is crucial that the scale of your scene corresponds to real-world data—otherwise the results will get corrupted.

A common mistake for example, is to import an airport at the size of a shoebox or a room at the size of a stadium. In one case, the lighting computation will be too bright, and in the other case, it will be too dark.

To verify your scale settings, check the “System Unit Scale” settings in the “Customize | Units Setup | System Unit Setup dialog box”:

System Units Setup of 3ds Max Design

Recommended Light Types

The recommended light type are the Photometric lights and the mrSun and mrSky . They simulate real-world values and play nice with indirect illumination computations and camera exposure.


52

Recommended Shadow Settings

The recommended shadow type for typical architectural rendering in 3ds Max Design is the Ray Traced Shadow type. While this might not have been true in the past, ray traced shadows are faster to compute than shadow maps, less memory intensive and handle transparency better. This is used by default in 3ds Max Design but not in 3ds Max.


53

Exposure Control

What is Exposure Control?

Physically based rendering requires exposure control, also called tone mapping. Tone mapping is the procedure of mapping a numeric lighting intensity in High Dynamic Range (HDR) from the scene into an RGB value of the pixels in the rendered frame.

Physical light intensities range from zero to numbers approaching infinity in bright sunlight. The range of contrast available on display monitors is limited compared to this dynamic range, and common image formats are even more limited: JPEG images are eight-bit images, ranging from a value of zero for black to 255 for white. In these files, white can only be 255 times brighter than black, a fraction of the range in the real world. Tone mapping helps compensate for the difference in range.

Here are a few examples of real-life scenes measured with a luminance meter:

Sky luminance at horizon and zenith: 2600 cd / 360 cd / m2. Luminance on the leaves: 500 cd / m2.

Moonlit backyard, luminance on the roof of the garage: 0.22 cd / m2. Kids” play set luminance (brightest): 0.1 cd /m2.


54

Assuming that the rendering engine can use real-world units for light sources (lumens, candela, or lux at distance) and real-world units for materials (reflectance), the resulting images will be beyond the range of what a monitor can display.

Therefore, it’s necessary to compress the calculated image (ranging from zero to infinity) into a displayable image (ranging from zero to 255). This process is called tone mapping or exposure.

To enable exposure control in 3ds Max Design, use the “Environment and Effects” dialog box:

Exposure Control Rollout in 3ds max Design

When you change the brightness and contrast controls, the light levels of your scene don’t change; only the sensitivity of your camera does. This is far better than adjusting each light source in a scene one by one. If you want to shoot a photo, you would be more likely to adjust your camera’s aperture or shutter speed than wait for the sun to set. The exposure controls control the appearance of the image in the same way than a SLR camera.

The top image is exposed toward the inside of the room, and the bottom image is exposed toward the outer courtyard. Both are correct the light levels in the scene did not changed; the direction of the exposure is up to you. (c) 2007 Electric Gobo / Karcher, www.electricgobo.com

http://www.electricgobo.com/


55

Recommended Exposure Control Settings:

The recommended Exposure Control plugin to use is the “mr Photographic Exposure Control”. It is designed to mimic real world camera settings and assumes that the scene environment is physically based as well (Sun, Sky, Photometric lights, proper scale etc.).

The mr Photographic Exposure Control is recommended.


56

Simplified mental ray render panel

The simplified mental ray render panel is meant to reduce the learning curve for Revit users and accelerate test renders by providing you fine tuning knobs for Shadows, Reflections and Refractions:

Glossy Refraction

Glossy Reflection

Soft Shadow

Edge Anti-aliasing

Launch the Exposure Control Panel

Enable/Disable Indirect Illumination Cache Indirect

Illumination to Disk


57

Exterior Day-time Rendering

Daylight System

The Daylight System of 3ds Max Design regroups 2 light sources in the same user interface: the Sun and the Sky. Their intensity and colors are ruled by their orientation in the 3D space, which is affected by the Time and Position on Earth. The blue background is handled by a special shader that must be assigned in the Environment map:

1. Create a Daylight System; make sure it uses the mrSun and mrSky plugins and set the Time and Date.

2. Enable the mrPhotographic Exposure Control and use the Exterior Daytime preset.

3. Assign a mrPhysicalSky shader in the environment Map slot: this will add the nice blue background:

4. Turn ON final gather: this will create the indirect illumination effect and become the Skylight.

5. Render: you should get something like this already:

(All Models in this section are based on an original file from: (c) 2007 Electric Gobo / Karcher, www.electricgobo.com)

Direct illumination from the mr Sun light object

Sky dome contribution comes from the mrSky light object + Final Gather

Background sky comes from the mr Physical Sky environment shader.


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Adding clouds in the sky

The mrPhysicalSky shader has the ability to change color and affect the appearance of the Sun Disk with the haze parameter. This parameter is map-able so it makes an excellent home for cloud maps:

1. Add a sky image in the Haze map of the mr Physical Sky. Don’t forget to use the proper projection (Screen or Spherical for example)

2. Increase the Output Value to ~8 to see the effect: this will drive the haze value of the Sky based on the image.

3. Render: the clouds now appear on top of the cloud. They also change color based on the time of the day.

A Haze map must provide values from a range to 0 to ~8 to be effective, hence the “boost” done with the Output Amount.

A cloud image (a simple photo) modulates the value of the Haze parameter of the procedural mr Physical Sky


59

Glare Shader (Bloom)

The Glare Shader is what we know as an “Output Shader”. Output shaders are processed on top of the final image, as a post processing step. They can be assigned in the Render Setup dialog.

1. Add a Glare shader in the Camera Effects | Output slot of the Renderer Tab (Render Setup dialog) and instance it in the Material Editor:

2. Increase the contrast in the Exposure control to let the Glare shader finding the hotspots.

3. The Spread parameter is the one that affects the most the image.

4. Render: you should see something like this:

The Glare Shader adds the small “spark” to the image.

Glare shader effect. The streak comes from the Streak image.


60

Exterior Day-Time Rendering Tips and Tricks

1. The illumination on the surfaces is provided by the Sun and Final Gather and not the Environment Map!

2. You do not need many Final Gather Bounces to have a meaningful effect: Final Gather bounces are usually useful for interiors.

3. The ground has an effect on indirect illumination: if you use a very bright green grass, your building will probably turn greenish as well.

4. To get the Glare shader working, you need a high contrast image: the Glare shader analyzes the rendered image and adds the “sparkles” to it. If the image is too faint, boost its contrast with the Burn parameter of the Exposure control.

5. Use the Exposure Preview to quickly preview the image’s brightness.


61

Interior Day-time Rendering

Sky Portals + Final Gather & Multiple Diffuse Bounces

The strategy do adopt with interior renderings is to identify windows and openings with a special light object that is called a “Sky Portal”. Its job is to focus rays from the environment through the windows and holes and avoid wasting a lot of rendering time with traditional Final Gather computation.

mr SkyPortal Light object positioned in front of a window, pointing inside the room

1. Once you are satisfied with an Exterior rendering, add a Sky portal in front of the windows of the building.

2. Make sure their arrow point inside the space as illustrated: this indicates the direction of the light flux.

3. Move your camera inside.

4. Change the Exposure control to an Interior Rendering preset: this will adjust the aperture of the camera to interior lighting conditions, which are darker than exterior spaces.

5. Increase the Final Gather diffuse bounces to ~3-4: this will bounce the light around inside the space.


62

6. Render: you should see something like this:

FG bounces determines the number of time light will bounce inside your space. A value from 3 to 5 is typically recommended for interior spaces.

Lighting is only from indirect illumination bounces.

Exterior is washed out because our exposure control is adjusted for interiors.

Soft and subtle direct shadows from the sky dome come from the mr SkyPortal light


63

Interior Day-Time Rendering Tips and Tricks

1. Use the Material Override from the Render Setup | Processing tab to understand the lighting distribution of your space. This will allow you to see the lighting effects on a neutral color as opposed to be distracted by reflections, refractions and textures Note, however, that you need to temporarily hide the glass panes in your windows, as this material override will turn them opaque as well, which will prevent the light from outside coming inside:

An interior rendering with the materials overridden by a neutral diffuse white material

2. Cache the Final Gather computation to disk: once it is baked to disk, you can re-render without recalculating indirect lighting (which can be time consuming) during material tweaks.

3. Use very low quality settings to tune your materials: the rendered image will be completed faster.

Global tuning knobs allows for faster control on all the scene materials and lights for faster tuning.

4. The Shadow Samples affects the quality (graininess) of the shadows from the Sky Portals. It is also controlled by the Global “Soft Shadows Precisions” slider in the Rendering panel:


64

Ambient Occlusion

Ambient occlusion has the benefit of enhancing the small details and creates what we commonly call “contact shadows”. Ambient occlusion is enabled directly in the A&D Material. Typically you will want to enable it for floors, door frames and other areas with fine geometric details.

Without Ambient Occlusion

With Ambient Occlusion

Typically, light leakage arises due to low

density of FG calculation .Objects appear to

be floating. Ambient Occlusion will help

solving this issue.

With Ambient Occlusion, edges are visually enhanced.

The larger the distance is, the more pronounced the effect will be. Usually, you want to use a distance of ~10 cm.


65

Interior Night-time Rendering

Photometric lights

We recommend using Photometric lights for interior renderings because their energy computation is physically based, which makes them ideal sources for indirect illumination calculations. The main reason for this is that the energy used in the indirect illumination process will always be in balance with the energy used for the direct illumination.

1. Start with an Exposure Control preset set as follow. You will re-adjust later but it’s a good starting point:

2. Create Photometric Lights in the space. As a reference here are typical intensities corresponding to real-world lighting values:

Class Wattage Type Intensity Beam Angle

Field Angle

Narrow 20 W Spotlight 3300cd 6 12

Narrow 20 W Spotlight 9150cd 12 25

Medium 50 W Spotlight 3000cd 25 50

Wide 20 W Spotlight 460cd 38 75

Wide 50 W Spotlight 1500cd 38 75


66

3. Turn OFF Final Gather and Render: you should get something like this where only the direct illumination is calculated:

Glow and self illumination

The A&D material exposes a Self Illumination feature that allows turning materials into a light source. The light transport is done via Final Gather so the quality of its shadows directly depends on the Final Gather accuracy.

1. Enable Self Illumination in a given A&D Material. You can decide if this contributes to Reflections and/or Illumination at the Material level. If you use a texture Map, the texture will modulate the color of the emissivity:

2. Turn Off all the lights to see its effect isolated.

Direct lighting only

A map can be used to simulate video walls of LED walls

The intensity rules how bright it is. Keep in mind that with Exposure Control enabled, you may find yourself having to go to relatively high values.

This is where you decide to contribute to the scene lighting or to reflections.


67

3. Render: You should get something like this:

Self illuminated material with contribution to Final Gather rays. No lights used in the scene.

Photometric lights turned back on with a color filter.

Final gather “sees” the luminous surfaces.


68

4. Enable Final Gather, with 3-4 Diffuse bounces:

Indirect lighting was bounced from the contribution of the direct lights.

The “splotches” are caused by low quality final gather settings. See the “Fine Tuning Indirect lighting” section for more tips on how to solve this.

With a better FG solution splotches disappear. See the “Fine Tuning Indirect lighting” section for more tips on how to achieve this.


69

Fine Tuning Indirect lighting

Basic strategy

To fine tune a Final Gather solution we recommend adopting the following strategy:

1. Bake the Final Gather solution to disk using your normal lighting conditions so you can re-use it later and lock it in a Read Only mode.

2. Use a Material Override with a Diffuse White Material: lighting is easier to visualize on a flat white surface. Since you locked the Final Gather solution, you don’t have to bother about transparent objects anymore, except for the light coming from outside your building (i/e/ the Sun).

3. Render with the Final Gather Diagnostics Mode (Render Setup Dialog | Processing Tab) to visualize the location of the Final Gather points contained in the FGM file:

4. Fine tune the interpolation settings: they can be changed even if your Final Gather solution has been locked.


70

Examples

Test A: Low Density, Low Interpolation

Observations:

We can see that the density of the Final Gather points is relatively low. The noticeable cloudiness is visible mainly where the Final Gather points are separated each other by a large distance (where the density is low). Since the Interpolation is also low, the result is the “cloudiness” effect.

“Cloudy” indirect lighting

Density relatively low


71

Test B: Increased Interpolation

Observations:

Here, we simply increased the Interpolation. We end up blending more Final Gather points together, a little bit like a “Blur” in an image. The Final Gather point’s density is still relatively low which did not increase the computation time.

Tip:

When a Final Gather solution is locked and read from disk, you can change the interpolation between each rendering without having to re-calculate the Final Gather solution.

By increasing the interpolation, we “blend” more points together, softening the solution.

Density still relatively low: no additional computation time.


72

Test C: Increased Density

Observations:

If we were to increase the density of Final Gather points to capture more subtle light effects and details, the Interpolation required is now larger: as we have more points, we need to blend more points together to reach a smooth effect. Notice the “cloudiness” effect appearing again when we used an Interpolation value of 150. To fix it, we need to increase it up to 450!

Note:

The reason for the noise is usually caused by the stochastic nature (randomness) of Final Gather. To solve it you either have to cast more rays per FG points or increase the Interpolation. Note that the Interpolation parameter is essentially a “blur” which can remove or reduce the effect of subtle shadows.

An Interpolation value of ~450 is better: the more FG points you have, the larger the interpolation needs to be.

With a very large density of FG points, an Interpolation value of 150 is not enough here. A larger Interpolation value is required to smooth out the results.


73

Non-Photo Real Renderings (NPR)

Ink & Paint Material

The Ink & Paint material gives a toon look to objects. It can respond to lighting and shadows or give a completely flat appearance:

Ink & Paint material

Tips:

5. The “Paint Levels” parameter of the Ink & Paint Material determines the numbers of gradients you will get on the material with lighting and shadows.

6. For typical cartoon looks, disable Exposure Control, Final Gather and use “Standard Lights”. Physically Based features generally don’t play nicely with this type of material

7. The quality of the Ink will improve with higher anti-aliasing.

8. You can use a Falloff Map to drive the color of the Ink based on distance, direction etc.


74

Ambient Occlusion & NPR

Often, it is useful to quickly render a series of draft views of interior shots with no materials simply to explore camera views. To accomplish this one technique consists into using Ambient Occlusion as a way to illuminate a scene to get a feel for the overall depth of the space:

Single A&D Material with an Ambient Occlusion Shader in the Diffuse Color

Single Ink & Paint Material with an Ambient Occlusion Shader in the Paint Color

Tips:

1. An Ambient Occlusion shader does not always have to return black or white. The look above was achieved by returning a dark blue and pale blue color.

2. The distance amount determines how much Ambient Occlusion will occur at the edges. Try to keep a value relatively low (i.e. ~10 centimetres) and increase as needed.

3. Combine Falloff Maps and Ambient Occlusion to develop interesting looks:

One of the Ambient Occlusion’s color is modulated by a Falloff Map


75

Lighting Analysis in 3ds Max Design

This section walks the reader through the various principles and workflows for carrying out an accurate daylight analysis in 3ds Max Design. The reader will learn some of the basic principles of daylight simulation and lighting analysis as well as how to build a scene, pick adequate material properties and set up the render settings for a physically accurate simulation.


76

What daylighting metrics do I want to calculate?

Many users might want to initially “see” a design under key times of the year such as solar noon on winter and summer solstice or other times that are relevant for the particular use of a space. HDR images can be used for such an exploratory, qualitative analysis.

As a design progresses, a user might want to further compare certain daylighting characteristics or “metrics” of a space to space to minimum requirements that are set by applicable standards and/or building rating systems. Two traditionally traditionally common daylighting metrics are the daylight factor and indoor illuminances under a CIE clear sky. Both of of these metrics can be calculated using 3ds Max Design as shown in the section 0


77

Analysis Output FAQs

How can I switch between lux and foot candles?

Lighting units can be changed from the Customize | Units dialog. You will be able to set your display as foot candles (Imperial) or lux (SI) units.

Can I export animation data in Microsoft Excel?

Yes. If you performed a lighting analysis calculation per frame (typically with Daylight running through the course of a day, month or year), exporting the data collected by Light Meters to a CSV file will let you load it into a spreadsheet program such as Microsoft Excel. Be aware though that the resulting output files can be very large and that you might have to analyze the data using Macros or a database system such as Microsoft Access.

Microsoft Excel opens exported *.CSV files as a single blob of text, what to do?

Usually, Microsoft Excel imports *.CSV files correctly (i.e. with columns and rows well separated. However, in some cases, it may load the *.CSV file exported from Light Meter objects as a single “blob” of text. If this happens to you will have to manually open the *.CSV file with the File | Open command and make sure you specify the “Text File (*.pm, *.txt, *.CSV)” option. This should launch a wizard that allows you to load the incoming data to specific rows and columns into a new spreadsheet.

Can I do lighting analysis with Photometric Lights? Do I need Daylighting for it to work?

Many people need lighting analysis tools for artificial lighting conditions (museums, theaters, schools etc.). This is a supported workflow with 3ds Max Design, i.e. you can do a lighting analysis without specifying a Daylight System. The workflow is identical except for that you have to specify Photometric Lights.

Why are my Light Meters all white in the viewport after the calculation has been completed?

Typically, this is caused by an incorrect range of illuminance values in the Pseudo Color display. Adjust them in the Lighting Analysis Assistant, in the General Tab.

Can I create curved Light Meters?

Not at the moment. Light Meters are constrained to rectangular shapes in 3ds Max Design. You can however use modifiers to bend their shape.


78

Rendering, Precision and Algorithms FAQs

Can I use another rendering engine than mental ray?

No. The lighting analysis features in 3ds Max Design are based on core mental ray features and cannot be used with other renderers such as the Default Scanline Renderer or other third Party Renderers.

What are the object types that are valid for lighting analysis in 3ds Max Design?

Lighting analysis results can only be guaranteed to be within physical correctness when you use a special subset of light sources and materials in 3ds Max Design.

Those are: mental ray renderer, A&D Material, ProMaterials, Photometric Lights and mrSun+Sky using the Perez or CIE sky model. Using any other type of material or light source may not prevent the lighting analysis data from being reported, but we cannot predict how accurate those numbers will be.

As for geometry, the type of geometry does not matter. It can be Editable Meshes, Polys, Patches, NURBS; as long as they are renderable by mental ray.

What controls the precision of light meters?

Light Meters are collecting illuminance at each point based on your mental ray Final Gather and Global Illumination settings. The more accurate your “pretty picture” renderings get; the more precise the illuminance is are going to be.

However, there is some tolerance built into this: Internally, Light Meters will cast 8 times more rays than what is set in the Final Gather settings. This means that even if the “pretty picture” you get is not totally noise free, the Light Meters numbers will be somewhat more accurate.

Note that this feature does not protect you from mistakes such as wrong material reflectance, incorrect glazing definition and non-physically based effects such as lights that may not cast shadows or attenuate. We hope that this document gives you enough information on this topic.

Can I use the IES sun and IES sky plug-ins?

Yes. They work well for the LEED 8.1 Credit, but would not work for daylight factors or climate based metrics.


79

My sky is greenish, how can I solve this?

While our test confirms that the light levels are unchanged by the Saturation parameter, the CIE sky has the tendency to create greenish images. If your goal is to create pretty pictures with light levels overlaid on top, you may want to reduce the Saturation of the mr Sky to 0.0 in order to get a grey image with the CIE sky.

Reducing the mr Sky Saturation to 0.0 will remove the green tint you may see in the rendered image. Note that this green tint does not affect the ligh levels reported by the Light Meters.

What are the best Final Gather settings to use?

The answer to this question depends on the complexity of your scene. Generally speaking, if you are satisfied with the way the image looks, the results should be pretty accurate. The image quality (thus lighting computation accuracy) is greatly influenced by the type of scene you are dealing with.

If your interior is a large atrium where the sky is visible from almost any location in space, chances are that this will be easily solved by a few bounces of light with a few rays per FG sample. If you have a closed interior that has small windows, chances are that the requirements for light bounces and rays per FG points will need to be a lot higher.

Do I need to use Global Illumination / Photons with mental ray?

No. In fact, we do recommend inexperienced users to stick to Final Gather only. Photons can be tricky to use, especially with Caustics. If you want to opt for Photons (they are definitively very fast to compute), keep in mind that by the nature of Photon Density requirements, if you plan to report light levels through Caustics, a receiving surface must be very close to the Light Meter. For example, you will not be able to measure light levels from Caustics effects with a Light Meter “floating” in the air.

Note: We have not validated the physical correctness of Photons yet, if you do validate them let us know!

Can I use sky portals?

Sky portals where not validated.


80

I used an overcast sky model and I still see the sun disk in the background and in reflections.

This is “normal” in a sense that in 3ds Max Design, illumination is separated from reflections and backgrounds. The reason why you see the Sun disk is that the Environment Map (mr Physical Sky map) always display it. To eliminate this, you can set its size to 0. Note that although the Sun may be visible in reflections and background, the lighting values reported by the Light Meters are not affected by this as the illumination comes from the mr Sun and mr Sky lights (wrapped inside the Daylight System).

A yellow image pops up after using the Lighting Analysis Image Overlay. Do I need it?

If you see a yellow image pop up after rendering, this is caused by the Lighting Analysis Image Overlay. This image is a temporary data buffer where luminances and illuminances are recorded for every pixel. You can close this dialog if you wish.

The yellow image is temporary data buffer that is used by the Lighting Analysis Overlay render effect. You can dismiss this dialog or prevent it from showing up by disabling the “Display Elements” from the Render Elements Tab.

Daylighting Metrics of this document.


81

3ds Max Design is further capable of loading in an EnergyPlus weather file (*.EPW) allowing it to automatically generate time series of HDR images and/or illuminances under multiple sky conditions. EnergyPlus weather files contain annual data for typical climatic conditions at a site including ambient temperature, relative humidity, wind speed and direction as well as direct and diffuse irradiances. EnergyPlus weather files for over 2000 locations world-wide can be downloaded from http://www.eere.energy.gov/buildings/energyplus/cfm/weather_data.cfm.

The ability of 3ds Max Design to generate time series of indoor illuminances is useful for users interested in optimizing a design with respect to local climatic conditions using one of the emerging climate-based daylighting metrics such as daylight autonomy and useful daylight illuminance. An introduction to these metrics is provided under http://irc.nrc-cnrc.gc.ca/pubs/fulltext/nrcc48669/.

Is the simulation tool capable of reliably calculating these metrics?

The answer to this question is generally difficult to find partly due to the scarcity of rigorous validation studies that compare daylighting measurements to simulation results and partly due to the fact that no simulation program can currently model any daylit situation. While modeling the daylight factor in a side lit rectangular space with a clear glazing might be a task that many simulation programs master, tool performances vary dramatically as more complex geometries or daylighting systems are investigated.

In order to help users decide which tool is appropriate for their particular model, a series of daylighting test cases was recently developed and 3ds Max Design was compared to these test cases. The comparison yielded that using the embedded mental ray engine and the Perez All Weather sky model - that both come with 3ds Max Design - the software is capable of modeling interior work plane illuminances from the test cases with a comparable accuracy as the Radiance backward raytracer (http://images.autodesk.com/adsk/files/3ds_max_design-exposure_validation.pdf).

The lighting analysis workflow

General Modeling Concerns

Lighting analysis is a form of 3D rendering where precise definitions of lights and materials are taken into account. Generally speaking, the same principles that apply to “pretty picture” renderings are just as valid for lighting analysis workflows. I.e. your geometric model has to be “clean” (without any holes etc.) .

Import Geometry

Create a daylight system

using the mr Sun and mr Sky

or place Photometric light sources

Place your camera where you want to do

your lighting analysis.

Make a preview render and adjust the

image’s exposure.

Use the Lighting Analysis

Assistant to inspect the

scene.

Report Light Levels.

•On the rendered image.

•In the viewport.

•In Microsoft Excel.

Determine the appropriate

metrics for your project.

http://www.eere.energy.gov/buildings/energyplus/cfm/weather_data.cfm

http://irc.nrc-cnrc.gc.ca/pubs/fulltext/nrcc48669/


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Create a ground plane around your building

If you don’t have an accurate 3D model and reflectance information about the surroundings of your building, start with a large ground plane around your building. In other words, do not let your building “float in air”. By modeling a large surface representing the ground, you allow daylight to be reflected off the ground and into your building. In order to mimic typical ground conditions, set your ground surface to a diffuse material with a RGB color of 0.20, 0.20, 0.20 (20% diffuse reflectance).

Note: Be careful to not create ground planes that cross-through your building. We have seen cases where the ground plane traverses the middle of an office space: this will affect the lighting reports negatively). If you have snow on the ground, you may have to work with different ground plane material properties.

A large surface with a diffuse material has been modeled around the building to represent the ground and alllow the daylight bounce back to the ceiling.

Setup the Daylight System

Lighting analysis in 3ds Max Design is based on the mental ray rendering engine. In short, if you can get a reasonably looking image (i.e. a “pretty picture”), the lighting levels reported by the lighting analysis tools should be accurate assuming that your render setting are high enough and that lights and materials were previously defined in a “physically correct” way.

Follow the steps described in the previous section of this document entitled Rendering in 3ds Max Basics.

Note about the mr Physical Sky Environment Map

The mr Physical Sky environment map is the sky background map. It is a purely cosmetic effect filling in the background of your render with a nice shade of blue representing a physical sky by taking into account the position of the Sun. It does not alter the light levels calculated by the renderer since these are calculated using the Skylight object.


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Click “Yes” if you are prompted to assign an Exposure Control to your scene. Click “Yes” if you are prompted to assign a mr Physical Sky as an Environment map. Make sure your Daylight System uses the mr Sun and mr Sky.

Specify Location and Time

The location and time of the Daylight System is defined in the Motion Panel. Don’t worry about the position of the Sun and Sky objects in the 3D viewport: this is purely used for visual representation. Internally, the Sun and Sky illumination is always computed from the extents of the 3D model, regardless its size. Feel free to position the Daylight System object anywhere within your scene.

To reach the Daylight System”s location and time control, select the Daylight System and switch to the Motion Panel.

The Orbital Scale parameter controls the height of the Daylight System in the viewports. Note that this does not affect the way the Sun and Sky render: they will always illuminate the scene from outside, even if the object is located inside of a room in your viewport.

Daylight System Orbital Scale

Next, adjust the Orbital Scale of the Daylight System object to move the Sun and Sky objects above your model as illustrated. This can be done via the Motion Panel. This does not change the way the scene is rendered or illuminated. It only moves the Sun and Sky lights along their axis for easier selection.


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The Orbital Scale parameter controls the height of the Daylight System in the viewports. Note that this does not affect the way the Sun and Sky render: they will always illuminate the scene from outside, even if the object is located inside a room in your viewport.

Aerial Perspective

Turn off the Aerial Perspective option in the mr Sky Advanced Parameters. Aerial Perspective is used to achieve aesthetic affects suitable for exterior renderings. It creates “fog” effects where distant building vanishes in the horizon and can interfere with the rendered images, especially for interior shots. It is ON by default in 3ds Max Design and should be OFF for any quantitative lighting analysis.

Make sure you turn off the Aerial Perspective, as it is a “nice picture” effect only.

Set the Ground Color to Black in the mr Sky.

The mr Sky Ground Color correspond to the diffuse reflectance of an infinite ground plane (“virtual ground”) that is created internally by mental ray at render time. While the Ground reflectance is correctly interpreted by the renderer, the main problem comes from the way it bounces rays from the Sun and Sky. Internally, the “virtual ground” bounces light rays from the Sun which is does not always match the Sun and Sky model you may have set in the UI. As a result, the renderer could bounce a lot more light than expected.

There is a simple workaround for this. First, set the Ground Color to black (zero reflectance). This will prevent the problem described previously from happening as the ground will absorb all incoming light.

The Ground Color must be set to black (RGB: 0,0,0) for prevent the internals of mental ray to bias the results incorrectly.


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Then, by modeling a ground plane, simply make sure the light that is bounced from it takes into account the Sun and Sky model you selected.

Perform basic test renderings

Make a preview render and adjust the image exposure

We are almost there! Prior to looking at any illuminance levels in the scene, we recommend that you run a few test renderings to verify whether the model looks “ok”. An initial visual inspection constitutes an important first quality control step that may help you to detect any modeling errors including holes within the geometry, a wrong material type or an improperly oriented Daylight System.

Also, as we will be overlying a grid of illuminance results on top of the visualization later in the process, it is a good idea to get this first step right up front.

A quick way to generate a preview render is to use the Render Preview tool in the Rendering | Environment | Exposure Control rollout. Go ahead and make a render preview in such a way that your Exposure is in the correct range.

Perform a quick test render and adjust the Exposure Control in order to get a reasonably good looking image first. You can do this from the Exposure Control Preview tool. Use the “Physically Based Lighting Indoor Daylight” preset as a starting point. Adjusting the Exposure Value (EV) will affect the image shown in the preview in real time. Once you are happy with the results, you can go further and make a large render preview..

Try a higher resolution test image

Once you are satisfied with the results from the preview, you can render a larger image by using the Rendering | Render command. This will bring up a rendering window (known as Frame Buffer in the 3ds Max). On the bottom part of the window you will find a few settings that control the speed and quality of your render.

The most important parameters for an accurate daylight simulation are the Image Precision, Final Gather Precision and Final Gather Bounces. For interior renderings, a Final Gather Bounces of 4 to 7 is recommended. The Final gather precision will reduce the “noise” within an image but will increase render times.


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Render window (Frame Buffer) with quality control parameters. A Final Gather Bouces of 4 to 7 is generally preferrable for interior spaces.


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Prepare for analysis with the Lighting Analysis Assistant

Now that you have a reasonably good looking image, you can start extracting light levels at any location within the space. The following four sections will walk you through the steps necessary to accomplish this task by helping you verify that all of your scene settings are in the realm of “physical correctness”.

The Lighting Analysis Assistant is designed to guide you through the process of checking the scene and raising flags about potential issues that may be found. For example, you may have a scene that uses “Standard Lights” as opposed to “Photometric Lights”. These light sources would be found by the Lighting Analysis Assistant and flagged as “invalid” to use.

Note: We do not recommend you to initiate the lighting analysis process until all items identified as invalid are resolved.

Please launch the Lighting Analysis Assistant via the top menu Lighting Analysis | Lighting Analysis Assistant.

The Lighting Analysis Assistant is a scene analyser that searches for incorrect rendering settings that may incorectly alter the results for the lighting simulation. You can launch it from the Lighting Analysis pull down menu. Click the “Update Status” button to refresh its content.

After launching the Lighting Analysis Assistant from the Lighting Analysis pull down menu, start with the General Tab.

General Tab

In the General tab you can adjust your basic render settings. For a physically based lighting calculation you will have to use the mental ray renderer within 3ds Max Design. Final Gather has to be enabled and the Renderer |

Check Render Settings for Physically Based

Rendering.

Check Light Sources for Physical Correctness.

Check Materials for "Valid" Types.

Create Light Meters.

Report Light Levels.

• In the 3D View with Light Meters

• On the Rendered Image with Image Overlay


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Frame Buffer Type set to 32 bit precision. The General Tab also lets you specify maximum and minimum levels for the pseudo color display for the Light Meter objects (see below).

General Tab of the Lighting Analysis Assistant

Lighting Tab

The Lighting Tab allows you to find “invalid” light types (such as Standard Lights and Standard Sunlight objects) within your scene and verify that the Daylight System is correctly set up. Shadow settings are also verified: All lights must use shadows that are ray traced to support transparency properly.

Lighting Tab of the Lighting Analysis Assistant

The Lighting Analysis Assistant expects “physically correct” shadow settings for all light sources.

Materials Tab

Use the Materials Tab to search for all non-physically based, “invalid” materials in your scene. These materials have to be replaced by physically based materials for a correct lighting analysis. Physically based, “valid” material types are mental ray “Architecture & Design Material” (A&D Mtl) and “Autodesk Materials”.


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The Materials Tab allows you to search and find non physically based materials in your scene that are incompatible with lighting analysis workflows. Here we show that this scene has 21 “invalid” materials which will need to be replaced.

You will need to replace all invalid with valid materials. A quick way to do this is to select all invalid objects and assign them a default “flat” finish Material. Keep in mind, however, that the color determines the amount of light reflecting from those materials (reflectance). You can deal with this at a later stage within your project. You also have to pay attention that you do not accidentally replace a window pane with the default opaque material.

If you need to quickly create a material with a default “flat” finish, we recommend that you use an Arch & Design Material assigned to a grey color of RGB 0.5 0.5 0.5 and use the “Matte Finish” template. This will be considered as a perfectly diffuse material that reflects 50% of the incoming light back into the scene.


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The process of checking materials is complete when the Lighting Analysis Assistant shows that 0 materials are found with invalid settings. Note: You have to click on the Update Status button in order to refresh the user interface of the Lighting Analysis Assistant.

Analysis output tab

The Analysis Output Tab of the Lighting Analysis Assistant regroups all functionality required to create light metering tools to extract light levels from your scene. It offers two modes of data reporting: Light Meters which are 3D objects located in space and Image Overlay which will overlay illuminance values projected from the screen on top of the rendered image.

The former type of data corresponds to one or several illuminance sensors located at key positions within a space such as the “work plane”. The latter output format helps a user to interpret simulation output in relation to the space. The next section describes how to enable those output options. The subsequent section (0


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Daylighting Metrics) will discuss various ways to calculate and interpret the simulation results.


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Report Light Levels

Light Meter Objects

Light Meters allow you to report incident lighting (illuminance) falling onto any point within a scene. You can create them as a three dimensional “grids” and correctly position them within your scene using the 3ds Max Design transform tools. Lighting grids can be animated as well, showing for example, changing indoor illuminance patterns over the course of a day or year.

You can create a Light Meter object from the Analysis Tab of the Lighting Analysis Assistant or from the Create | Helper Panel.

Light meters do not affect the scene (they do not block or bounce light) so they can cover any area. Each subdivision represents a point at which incident illuminance normal to the grid will be measured (calculated). As a consequence, the denser the subdivisions are, the longer a simulation will take. Typical grid resolutions are in the order of 1ft x1 ft or 0.5 m x 0.5 m.

A Light Meter object has been created in the 3D space, at the workplane position; ~30 inches above the floor. It covers the entire room area and has a relatively coarse subdivision. Light levels will be reported at each intersection.

Once all Light Meters have been created - and you have successfully gone through all the steps described in the previous sections of this document -, you can hit the “Calculate All Light Meters” button. This will initiate a lighting calculation process for the Light Meters only. At the end of the process, the calculated Illuminance values will be displayed on the Light Meters in the 3D viewport.

Note: Keep in mind that the Light Meter calculation uses the rendering parameter defined in the Rendering Settings dialog. For example, if Indirect Illumination calculation is turned off, the Light Meters will ignore indirect lighting.


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A Light Meter object has been created in the 3D space, at the workplane position; ~30 inches above the floor. It covers the entire room area and has a relatively coarse subdivision. Light levels will be reported at each intersection.

To change the color range of the Pseudo Color display of the Light Meters, go in the Lighting Analysis Assistant | General tab and set the Min / Max ranges. Note that this does not affect the calculated values. Note that it only affects the color on the Light Meters and not the light levels themselves.

Pseudo Color range is adjusted for the Light Meters in the Lighting Analysis Assistant | General tab.

The Lighting Units (lux or foot candles) can be changed in the Customize | Units dialog.

Once the data has been calculated, you can export it to a *.CSV file (format readable by Microsoft Excel) for further analysis. The generated data contains Illuminance values for each calculated point, for every frame of your animation. Depending on the complexity of your project, you may want to consider using a database system such as Microsoft Access to run custom queries and formulas as the data set may be cumbersome to deal with otherwise.

Rendered Image Overlay

For presentation purposes, it is useful to overlay light levels on top of the rendered image (on top of the “pretty picture”). This helps putting the results into context. To help you with this task, another method is available to you, which is called the “Lighting Analysis Image Overlay”.


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In 3ds max Design terms, this is implemented as a “Render Effect”. This tool will basically print numbers in pseudo color form on top of the rendered image. You can enable this feature from the Lighting Analysis Assistant or from the Lighting Analysis | Create | Lighting Analysis Image Overlay.

The Lighting Analysis Image Overlay render effect must be added in the Effects panel to be enabled.

Showing light levels from Light Meters overlaid on the rendered image

To show numbers calculated from the Light Meters on your rendered image, use the “Show Numbers from Light Metering Helper Objects” option in the Lighting Analysis Image Overlay Render Effect.

Lighting Analysis Image Overlay showing numbers from Light Meter Objects.

Showing light levels projected from the Camera overlaid on the rendered image

Another approach is to report numbers on the image as if a grid was projected from the camera. This is convenient when statistical analysis is less important but presenting an idea of the light levels in a complex space is needed.


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Note: Keep in mind that this type of projection is view dependent and numbers correspond to the intersection of a ray projected from the Camera into the scene. As a result, they will be a mix of points on the floor, ceiling, walls and furniture.

“Show Numers on Entire Image (Screen Grid)” option in the Lighting Analysis Image Overlay Render Effect is now used.. The Screen Grid layout Options manages the density of the grid on screen.

Now that you know how to access and use the various analysis tools in 3ds Max Design, the next section will provide you with some suggestions of what to might want to calculate and how to analyze your results.


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Daylighting Metrics

In this section three different daylighting metrics and pertaining simulation workflows are discussed and some very basic directions are provided which of these metrics might be most adequate for your particular project. The three metrics are daylight factor, CIE clear sky illuminances and climate-based metrics.

Daylight Factor

The daylight factor is defined as the ratio of the internal illuminance at a point in a building to the unshaded, external horizontal illuminance under a CIE overcast sky. The CIE overcast sky is a standardized description of a completely overcast sky, meaning that the cloud cover is continuous and no “blue” sky is visible. In contrast, a sky with partial cloud cover is often referred to as an “intermediate” CIE sky. A “clear” CIE sky has no clouds.

The CIE (International Commission on Illumination) has defined standard sky luminance distributions for all three types (see Figure below). More recently, the CIE diversified into a larger number of intermediate, standardized skies. 3ds Max Design supports the two extreme CIE sky conditions, overcast and clear. For intermediate skies the “Perez All Weather” sky model” has been implemented (see below).

CIE overcast sky CIE intermediate sky CIE clear sky

Visualisation of the sky luminous distribution of the standard CIEvovercast, intermediate and clear skies.


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Calculating the Daylight Factor

The CIE overcast sky is accessible in the mr Sky interface, under the “Sky Model” drop down as illustrated below. It will control automatically the balance between the illumination coming from the Sunlight and the Sky dome (mr Sun and mr Sky) based on the Diffuse and Direct Illuminance parameters. To obtain a fully overcast sky, set the Direct Normal Illuminance to 0 (meaning that you have no light directly coming from the Sun).

The mr Sky set to use the CIE Overcast Sky model.

Once you have run a lighting simulation under a CIE overcast sky, daylight factor results are accessible for all Light Meter objects. All you need to do is to set the “Values to Display” radio button to “Daylight Factor” as illustrated below. The Light Meters will calculate illuminances at each point as usual but the values will be reported in percentage (%) values corresponding to the Daylight Factor. I.e. simulated illuminances are divided by the

horizontal outside illuminance that was earlier specified under the mr Sky interface.

Please note that the daylight factor is independent of the outside horizontal illuminance whereas total and diffuse

illuminances depend on it.

Note: This is option only available when the CIE sky model is used.

Change the Values to Display to the Daylight Factor mode on Light Meter Objects. When exported to *.CSV files, Light Meters also report the Daylight Factor in a dedicated column.


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Towards Climate Based Metrics

As explained above, the daylight factor - for mainly overcast climates – and CIE clear sky illuminances - for mostly sunny climates - provide you with some meaningful ways to optimize your daylighting design. For a more hybrid climate you have to work with both metrics to make sure that your design “works” under both types of skies. This approach will lead to reasonable daylighting designs.

An emerging, more holistic way of analyzing the daylighting within a space is to use so called “climate-based” metrics. These metrics are based on a very large number of sky conditions, typically all hourly or even sub-hourly sky conditions within a given year. In practice these sky conditions can be generated using a “weather file” for your particular building site.

Annual weather files contain typical environmental conditions for a particular site based on several years of measured data. A common file format is the US Department of Energy’s EnergyPlus weather data format (*.EPW). Several thousand EPW files are available free-of-charge from http://www.eere.energy.gov/buildings/energyplus/cfm/weather_data.cfm.

3ds Max Design can read in EPW files and combine them with the Perez All Weather sky model allowing the software to model daylighting conditions during all hours of the year.

Enabling the Perez Sky Model and Loading an EPW File

In order to use the Perez sky model in combination with an EPW file you have to select ‘Perez All Weather’ under the mr Sky Parameters and provide diffuse and direct outside horizontal illuminances.

The mr Sky set to Perez All Weather model. Select this sky type if you desire to do lighting analysis with weather data files.

First, download the *.EPW file of your choice from the Energy Plus website. You can browse by region and city in the Weather Data section of the website.

http://www.eere.energy.gov/buildings/energyplus/cfm/weather_data.cfm


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The Energy Plus website allows you to browse by regions for weather data files.

Locate the EPW symbol matching the region of your choice and “Save Target As..”

Once the *.EPW file has been saved on your disk, load it in the Daylight System of your 3ds Max Design project.

Tip: Use the Scene Explorer to locate and select the Daylight System from a list view as opposed to selected by picking in the scene.

When you load an EPW file into 3ds Max Design, the software resets the azimuth and altitude of the Daylight System according to the information provided in the EPW file. Depending on the date and time you pick the software also resets the direct and diffuse outside illuminance used by the Perez All Weather sky model.


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The Daylight System can be driven from a weather file. Use the Weather Data File option and click Setup... to enable this functionnality.

Setting the animation range of your simulation

The Weather Data File configuration dialog allows you to select the EPW file of your choice and determine the range of data (time period) you will want to use to perform your calculations. You can configure it to use a specific entry in the file (a single Date/Time) or you can set a starting point and an ending point in the Weather Data File to perform an animation.

A Weather Data File has been loaded and a fixed period from the file has been selected. A period corresponds to an entry in the Weather Data File (row).

If you desire to perform a lighting analysis study as an animation you must specify a Start and End point in the Weather Data File configuration dialog. By matching the 3ds Max Design timeline you will end up with an animation corresponding to exactly one rendered frame per entry in the Weather Data File.


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Specify an animation by identifying a Start and End point in the Weather Data File.

Match Timeline will change the 3ds Max Design animation ranges to fit the selected Start and End points.

Once a Weather Data File has been selected and configured, the Daylight System orientation and illuminances will be controlled from the file. As you scrub the timeline, you will see the values changing.

Once a Weather Data File has been loaded in the Daylight System, you can confirm that the Illuminances values are read from the file: The controls will be greyed out in the user interface but their values will change from frame to frame in real-time.

Reporting light levels over a period of time

After having set your Daylight System to pull data from a Weather Data File over a period of time via the 3ds Max Design animation system (timeline), you can now create Light Meters and run the calculation for the entire animation range using the Render Setup dialog.

Once the simulation is completed you can export simulation results for every frame (time step) and Light Meter into a *.csv file. Be aware that the resulting output files can be very large and that you might have to analyze the data using Macros or a database system.


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Light Meters collect light levels for every rendered frame. At the end of the process, you can export to a *.CSV file and inspect the data for every Light Meter point, at every frame. The number of frames depend on the length of your animation, which can be set by matching the timeline in the Weather Data File configuration dialog.


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Materials and Finishes for Lighting Analysis

To produce accurate lighting analysis results, you should consider not only the light sources but the Materials definitions. For those to be correctly defined, you need to understand how the mental ray renderer expects them to be defined. The following section covers the basis of defining physically correct materials.

Note: The following section merely provides some initial leads on the topic. If you want to dig more into it, you may want to consult the following document from the CIBSE: http://www.cibse.org/index.cfm?go=publications.view&item=164

The ‘problem’

While many graphical user interfaces allow users to specify RGB colors via color pickers, the resulting RGB value used by a simulation doesn’t usually correspond to the color displayed on your computer screen. As a result, picking a color based on the appearance of that color on your screen will lead to physically wrong outcomes.

What is the right red to pick for this apple? It can be difficult to tell and trust what you see on screen.

Diffuse Color versus Diffuse Reflectance

It is really about “absolute reflectivity” not “perceived color”...

In the end, the apple will still reflect the same amount of light whether you look at it under bright sunlight or dim living room light. Your eyes won’t perceive it the same way, but that doesn’t mean that the apple’s physical properties have changed.

No matter which type of material you use, the amount of light bounced back to the scene has a direct relationship with the material’s color. For example, a white wall reflects more light than a dark gray wall. A dark gray wall in sunlight reflects more light than a white wall in a dim room. This is the behaviour of diffuse reflectance. This is not to be confused with glossiness (for glossy or matte finishes).

All indirect light bounces off surfaces in a diffuse manner in all directions (also known as “Lambertian”). In contrast, directed bouncing light, such as the pattern of a mirror in sunlight, is called a caustic or specular reflection.


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Typically, for physically based raytracers, the diffuse color of a material is in fact a diffuse reflectance value; where 0.5 means that the material reflects 50% of the incoming light for all R, G and B components’. For example, a white wall will not reflect more than about 90% of the light it receives. Therefore, the RGB color should not be more than 0.90, 0.90, 0.90 (floating point colors) or 230, 230, 230 (integer colors).

A white wall (90% reflectance) reflects twice as much light than a grey wall (45% reflectance). This is directly caused by the diffuse color of the materials.

To select the desired diffuse reflectance, select the tint (Hue) of your material and then rely on the “V” value, which usually closely matches the reflectance of your material.

A RGB value of 0.5, 0.5, 0.5 for the diffuse color of a material represents a diffuse reflectance of 50%. This is also mathematically equivalent to a Saturation of 0.0 and a Value of 0.5 in HSV space.

A material with a perfectly white diffuse color correspond (from a rendering point of view) to a diffuse reflectance of 100%. This is too reflective for a wall or a ceiling. Normally, white paint should be around RGB 0.90,0.90,0.90 (90% reflectance).


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Estimating Material Reflectance

You can purchase a reference color chart that can help estimate the diffuse reflectance of materials by doing a quick eye ball comparison. A popular one, the GretagMacbeth ColorChecker

TM is sold by X-Rite (http://www.x-

rite.com) for roughly 80.00 USD. Those cards have calibrated colors and the reflectance of each swatch is published and known.

For example, the patch #22 (called “neutral 5”) has a diffuse reflectance of 19%. This means that for a rendering engine, the correct RGB value would be R0.19, G0.19, and B0.19.

Patch name Diffuse reflectance

Corresponding RGB color

white 9.5 (.05 D) 90.94 .9094

neutral 8 (.23 D) 58.50 .585

neutral 6.5 (.44 D) 35.71 .3571

neutral 5 (.70 D) 19.12 .1912

neutral 3.5 (1.05 D) 8.87 .0887

black 2 (1.5 D) 3.17 .0317

The industry standard GretagMacbeth ColorCheckerTM

has known reflectance values that can be used to compare against other finishes. Here, we are listing the reflectances of the lower row of swatches (white to black).

http://www.x-rite.com/

http://www.x-rite.com/


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By eye balling, we deduct that the average reflectance of the pavement is roughly 20%: its brightness is close to the swatch #22 on the chart which has a knownreflectance of 20%. This level of precision is good enough for a most lighting analysis workflows.

Wall Paints and Color Books

Paint manufacturers usually indicate the average diffuse reflectance of all their colors. Be careful: don’t confuse Diffuse Reflectance with the finish such as eggshell, flat, or semi gloss, which is more descriptive of specularity (glossiness).

Look for a “R XXX” or “LRV” in the back of color swatches from paint manufacturers, that usually represent the Diffuse Reflectance value.

When working with 3ds Max Design, be careful with color books provided with software packages or on the web. Several software packages provide color books based on manufacturer content. For example, the Adobe

®

Photoshop® application provides Pantone

® colors, and AutoCAD provides RAL and DIC colors. You can even find

color books from paint manufacturers such as Benjamin Moore (http://www.benjaminmoore.com).

However, these colors are not defined with global illumination rendering in mind. They are approximations based on display, lighting conditions, and gamma settings, making them a little bit unpredictable with Global Illumination rendering engines.

We have found that a Pantone color selected in AutoCAD or Photoshop software, will not generally process correctly with a GI renderer. Using a Pantone color supplied by a client may be better than eyeballing it, but be aware that you are not running a physical simulation. Check the rules in this document to make sure your approximated color does not exceed reflectance values from the real world. Darken the color if necessary.

http://www.benjaminmoore.com/


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Textures Maps

As previously described, the amount of light bounced from a material is defined by its diffuse color. With textures, the reflectance of the material is defined by every pixel.

As a result, if the texture is overly bright, incorrectly gamma corrected, or if your digital camera / scanner is not calibrated properly your texture will provide wrong reflectance values to the renderer and consequently lighting analysis reports will be incorrect.

Calibrating digital cameras, scanners and gamma correction workflows are beyond the scope of this section. If you are unfamiliar with these processes,, we recommend you remove all textures from your model and assume average reflectance values using grey shades.

Materials and Finishes for Lighting Analysis FAQs

I imported my scene from Revit: Are my materials accurate?

Not necessarily. While materials imported from Revit via FBX are of a valid type for analysis, nothing guarantees that their color (reflectance) matches the physical properties that are determined by your project.

In many cases, we have seen that Revit users select an overly bright color or use uncalibrated textures maps which introduce incorrect reflectance values in the model.

We always recommend that you verify whether the materials used by the simulation are set to plausible reflectance values. In other words, do not trust the Revit user who handed off a “nicely renderable” model. A correct visual appearance does not guarantee that glazing and walls properties have been set accurately.

Can I use texture maps on my materials for accurate analysis?

Yes, but it this will require to go through several calibration steps and is not recommended for beginners. If you are not in a calibrated environment where image gamma and color calibration have been taken into account, your lighting analysis results will be incorrect. Avoid textures and colors on your surfaces if you are not familiar with the relevant conversion processes and use grey shades instead.


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Glass and Glazing for Lighting Analysis

Depending on your needs, the mental ray engine has the ability to either attenuate light rays through volumes or not. As ray tracing is intimately related to the geometry of your model, especially with transparent object, it is important to establish a strategy for modeling glazing assemblies for lighting analysis.

The following section will describe the main workflows to create the type of glass you need and provide information on their application for lighting analysis workflows.

Solid glass with attenuation and refraction through volumes

For a total physical simulation of solid glass, you could model every sheet of glass as a real solid object and set the renderer to attenuate light correctly as it traverses the volume. This requires “caustics” effects to be enabled to handle glass refraction inside the volumes correctly.

While this is technically possible, this is overkill for typical analysis workflows: the complexity is increased both for the user and the processing power required.

A solid glass material where light attenuates inside the volume enables you to really perceive the thickness variation of the glass. This is nice for special effects and “pretty pictures” but overkill for typical lighting analysis workflows. To acheive this, you need to exploit the “caustics” feature of mental ray and the Color at Max Distance for Refractions in the A&D material.

Instead, we recommend using another modeling strategy, which is described next.


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Glazing as monolithic (solid) geometry, without attenuation and refraction inside volumes

We recommend you model glass panes as solid boxes and tell the renderer to not attenuate or refract light inside the volumes. This will let the raytracer casting rays through windows without having to refract light inside the geometry.

With this technique, the glass panes will more or less turn into “gel filters” where light energy is attenuated (which is what you want) but refraction and distortion of light will not be taken into account (this will save rendering time).

Solid objects where attenuation inside volumes and refraction is disabled. This is a perfect strategy for architectural glazing and lighting analysis. Notice how light attenuates (shadows) without being refracted. The material acts as a pure”gel filter”, which works well for glass panes. Obviously, on curved objects this looks unnatural.

Note: This is how most Revit models are defined: a solid box representing the total thickness of the glazing assembly where one polygon is facing inside the building and another is facing outside, regardless if it represents a single sheet of glass, a double pane or triple pane insulating glazing system.

Here is how it works: the Transparency Color of your material (typically the A&D material or Autodesk Glazing will attenuate light rays for each polygon that is traversed, without refracting it. Light will only be filtered by a faint color.

For example, if you modeled a triple glazing system where the thickness of the glass panes is physically represented, you will have 6 polygons to traverse. Therefore, if 6% of the light was lost after traversing each polygon (a Transparency Color set to 0.94), we would end up with a total glass transmissivity of 0.94 * 0.94 *0.94 *0.94 *0.94 *0.94 = 69%, which is plausible for a triple glazing system.

Each polygon traversed by a ray of light that looses 6% of the initial energy, for a total of 69% energy left on the other side of the glazing assembly. This amount of loss is ruled by the Transparency Color in the A&D Material. Attenuation happens each time a polygon is traversed by a light ray.


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To create a similar material in 3ds Max Design, you have 2 options: use the Architecture and Design (A&D) Material or the Autodesk Glazing Material. For the A&D Material, define the Diffuse, Reflection and Refraction parameters as illustrated. Note that

To create glass, the Diffuse Level must be set to 0.0, Reflectvity Level and Color must be set to 1.0, Transparency Level must be set to 1.0 and Transparency Color set to the desired transmittance value (0.94 in our case). The IOR set to 1.5 will represent generic Glass. Finally the A&D materialmust be prevented from attenuating and refracting through volumes in the Advanced Rendering Options.

If you want to make your life easier, the ProMaterial Glazing is already built-in to handle the case described above. Since you want to create a solid glass layer that attenuates light by a factor of 88%, all you need to do is to specify the Transmittance of the ProMaterial Glazing Material to 0.88 and instruct it that this applies when traversing 2 polygons.

Glazing Material set to attenuate light by a factor of 12% after traversing 2 polygons will produce identical results as the case described previously.


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Metal Coated Glazing

It is currently not possible to simulate metallic coatings where the transmittance and reflectance of glazing systems does not obey to the traditional Fresnel falloff curve.

Translucent Glazing

Although the mental ray Architectural & Design Material shader has the capability of weighting specular transmittance (clear) and diffuse transmittance (translucent), we have no formal study that proves that the resulting luminance and illuminance levels are accurate.

Please see this website: http://www.pfbreton.com/?s=glazing (search for “glazing”).

Importing Radiance Materials (*.rad files) exported from the Optics 5 software

You can manually extract the information provided by these files and convert them into a physically correct 3ds Max material.

Please see this website: http://www.pfbreton.com/?s=glazing (search for “glazing”).

http://www.pfbreton.com/?s=glazing

http://www.pfbreton.com/?s=glazing


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Color Management Techniques An overview of the techniques and limitations around color management and calibration will be provided. You will learn how to deal with the problem of capturing textures properly, load them in Autodesk® 3ds Max® appropriately and render out images with the correct color settings.


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Basics of color management

What tools are available to you?

Color management is there to insure that the colors you display on screen or on paper are consistent and coherent. A critical requirement is obviously associated with color measurement and control.

A (portable) spectrophotometer can measure the response curve of your computer screens and printers. This information is then looped back to your image editing software to obtain something closely matching an “idealized goal”.

One example of such device is the ColorMunki manufactured by X-Rite.

A portable spectrophotometer can define the response curve of your computer screens and printers.

Color management workflow example with Adobe Photoshop

Step 1: Profile your monitor

A color profile will be generated by your calibration device for your monitor. In my case, a ColorMunki was used to create a color profile that is automatically assigned in the display preferences of Windows via an ICC file.

This process happens automatically so I will save you the details of where, how and what …

If you do not have a spectrophotometer handy, you can minimally rely on built-in calibration wizards that come with your graphic card driver (My nVidia driver has, for example a brightness and contrast adjustment wizard that does a good job).

Step 2: Profile your printer

Similarly, the ColorMunki runs you through a wizard that prints a few sample swatches on a color printer. Those swatches are measured back and a color profile is generated. This profile is loaded/installed in Photoshop automatically as well.


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Note: Repeat the process for each type of paper you might use in your printer as each profile takes into account the whiteness of the paper that was used during the calibration process.

Step 3: Enable color management policies in Photoshop

You are now ready to benefit from color management so you must instruct Photoshop to work with color management. This is available under Edit | Color Settings…

At this point, you also need to make a decision about the working space color profile. To remain as compatible as possible with 3ds Max, I recommend you to use to the sRGB IEC61966-2.1 profile as illustrated below.

If you are doing mainly work with 3ds max, or print images with services available in large stores (Wallmart, Cosc etc), I recommend you to base your work on the sRGB profile. This is the lowest common denominator that is supported everywhere.

Gotcha!: One common mistake to do here is to select the monitor profile that may have been generated by the monitor calibration device (Ex: Display01.icm created by a ColorMunki). Don’t do that!

Turn on the “Ask when opening” option. You will be able to assign your default profile on file open if the incoming file profile mismatches yours.


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Step 4: Load an image in Photoshop

Most images created with digital cameras or scanners have a color profile embedded into them as Meta information. This color profile can be inspected in Adobe Bridge as illustrated here:

A color profile is usually associated with an image.

If you open an image that has a different profile than your working space (Adobe RGB vs sRGB in this current example), you may see this dialog:

Photoshop detected that the incoming image had a different profile than the workspace.

Knowing what each profile does is not really a concern to you in the moment. It is data that is used by Photoshop to convert pixel colors into something that closely matches the color gamut (range) of your display.

My recommendation is to convert it to the working space (because we established that 3ds Max is closely compatible to sRGB in a previous step).


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Step 5: Printing from Photoshop

Printing an image you see on screen requires what we call “Proofing” colors. The main reason is that the perception of color on paper is different than the screen: one emits light; the other absorbs light so they cannot be compared by using the same color profiles.

Fortunately, Photoshop has a built-in tool that can emulate colors that can be reproduced by your printer. This is available under View | Proof colors..

Configure the Proof Colors to match your target output (printer + paper profile).

Once you look at colors on screen under the “Proof Colors” mode, you can go ahead and adjust the image to look like you want it to look. If the image looks a bit faint, do not worry, this is normal: the “Proof Colors” mode try to emulate printed paper. Since paper do not emit light like your screen, the result will necessarily be faint as well. This is where you need to fine tune the brightness and contrast of the image to give it a bit more punch.

This is where you use the color profile defined by the Printer Calibration step in Step 2.

You may have multiple types of papers. Remember to select the one that matches your target printer / paper combination.


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Images viewed under proofing vs. under normal conditions.

Once you are ready to print, instruct Photoshop to manage the colors, by using the same printer profile as the one used to proof the colors in the previous step:

Photoshop Print Configuration Dialog with Color Management enabled.

The resulting print output will be as close as possible to the image you saw on screen. Trying it is adopting it

Image seen under “Proof Colors” mode, using a target output matching my printer profile.

If your intention is to print the image, adjusting final contrast settings should be done in that mode.

Pick the same profile as the one you picked under the “Proof Colors” mode.


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The “Linear Workflow” - Color management applied to rendering

Light is “linear”

One aspect that is critical to understand in 3D rendering is how light is interacting with material reflectance. In the following example, we demonstrate that changing the reflectance of the wall from 90% to 45% (divide by two (2)) also divides by two (2) the amount of light that bounce back in the room.

Light is MULTIPLIED with the reflectance (color) of the wall:

Making the color of a wall twice as dark will reduce the amount of light in the room by a factor of two.

Similarly, using a single light source instead of two will also produce the same effect: we get half of the light back in the scene as in the previous example.

Light can be ADDED or SUBTRACTED:

Using a single light source will reduce the amount of light in the room by a factor of two.


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Here is simplified math behind the phenomena:

Wall Luminance (cd/m2) = Light Quantity (lux) * Material Reflectance (color) / PI

As you can see, this is simple maths that only implies simple multiplications, divisions and additions. Light is calculated using linear algebra. The more light sources you have, the more light you get. This is why we refer to it as LINEAR SPACE.

Guess what? 3D Rendering engines also work that way: they ADD lights together and MULTIPLY them with the color of the materials to obtain luminance. 3D Renderers calculate in LINEAR SPACE.

Display encoding vs. Data encoding

Introduction to Gamma correction

Texture maps become an issue. As you previously seen, 3D rendering engines expect to calculate lighting in linear space. However, it is possible that material colors are not taking that into account. With flat colors (i.e. diffuse color picked from a color picker) this is easily done: material with a RGB 0.45 0.45 0.45 will reflect 45% of the incoming light.

With image files used as textures, it is another story…

Display systems having their own inherent characteristics that are not perceptually uniform. Typically, images displayed “as-is” appear incorrect to the human eye. To counteract this, an adjustment is introduced. This adjustment is known as “Gamma Correction”.

http://en.wikipedia.org/wiki/Gamma_correction

Gamma Corrected 50% grey: Appear correct on display, feed incorrect (too bright) reflectance data to 3D renderers

http://en.wikipedia.org/wiki/Gamma_correction


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Linear Space 50% grey: Appears too dark on display, feed correct (not too bright) reflectance data to 3D renderers

Gamma correction graph

Here is the dilemma: images must be gamma corrected for display purposes (so they look good), but this creates a situation where physically incorrect data can be feed to 3D rendering engines if this is not taken into account. Therefore, 3D rendering engines must “De-Gamma” the image textures prior to perform any light calculations. This “De-Gamma” correction will bring back the image textures into a LINEAR SPACE.

In summary, images used as data to perform calculation – or used to feed a numerical value to the renderer (diffuse textures, bump maps, normal maps) must be in linear space from the point of view of the 3D renderer while images used for display must be gamma corrected to look good (i.e. non-linear space).


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When should we apply Gamma correction on images?

In general, we are looking at the following data flow:

Data flow for a diffuse texture that “looks good” on screen passed to the 3D renderer in a physically correct way.

This is achieved in 3ds by enabling the Gamma and LUT preferences:

3ds Max: Customize | Preferences… | Gamma and LUT dialog

3ds Max: Image File Browse Dialog: this is where you can define a” per bitmap” Gamma correction value.

Image File saved with

sRGB profile from

Photoshop

De-Gamma 2.2

Bitmap Node (linearized

colors) Material

Physically Correct!

Input Gamma: when 3ds max loads an image from disk.

Leave at 2.2 for diffuse textures.

Output Gamma: when 3ds max saves an image to disk. Leave at 1.0 if rendering out to HDR or EXR, 2.2 if rendering out to TIFF, JPG or PNG.

“System Default” will use the values from the Preferences dialog.

“Override” will let you override the Gamma values for a specific Bitmap. Typically used for HDR output (see below).

Note: Avoid the “Use Image’s Gamma, its buggy and unreliable.


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Apply Gamma correction with a value of 2.2 for…

Diffuse texture maps saved from Photoshop with an embedded sRGB color profile.

Images saved from 3ds Max in a low dynamic range format (JPG, PNG, TIFF, TGA, PNG).

Leave Gamma correction at a value of 1.0 for…

Displacement maps or bump maps painted in Photoshop where the pixel values on screen represent actual

height values.

Normal Maps.

HDR images used as a background or environment map.

HDR images rendered to disk.


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HDR Imaging This section will demonstrate how a linear color workflow can bring flexibility in image compositing software. We will explore how HDR imaging can be used to change lighting scenarios in real time and how render elements can be leveraged for controlling objects reflectivity, indirect lighting, and image exposure. This applies to V-Ray™ users as well as mental ray® users, Adobe® Photoshop® (32bit), and Autodesk Composite users


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Using High Dynamic Range (HDR) images as backgrounds images

Introduction to HDR imaging

Problem: a camera does not respond the same way your eye/brain does

If you take a picture of an interior scene lit by daylight where the exterior is visible, you cannot get good exposure on the exterior and the interior at the same time.

Left image: exposure is correct for the interior but too bright for the exterior. Right image, exposure is correct for the exterior, but too dark for the interior.

The problems are multiple:

The camera cannot capture both interior and exterior zones at the same time without clamping colors to dark or

white pixels.

The image format in which the data is stored is limited in dynamic range: a JPG stores data in 8 bit per channel

(rgb), which can only accommodate 256 possible levels of brightness (2^8 = 256).

The resulting image is far from being close to what you perceived when you took the picture. In fact, your eye /

brain are capable of clearly seeing the interior and the exterior at the same time, but when you look at the picture

on screen, you don’t get the same perception.

Your perception of the final image varies depending on the hardware you are using, the quality of your monitor

etc.

How to solve those problems?

Step 1: Data Acquisition: capture all the luminance range of the scene and store them into a single image file.

To overcome the problem of limited ranges from cameras, a common technique consists into taking several pictures at different exposures as illustrated:


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We can capture the entire range of luminance by taking several pictures of the same scene at various exposures.

Then, we combine the pictures into what is known as a high dynamic range (HDR) image. The most common formats are:

*.pic, *.hdr (Radiance image format)

*.exr (Open EXR image format)

*.psd (Photoshop)

Software products such as Photoshop or HDR Shop have built-in capabilities to create HDR images from a series of low dynamic range photographs.

By using advanced image manipulation techniques1, it is possible to determine the response curve of the camera

and calibrate the HDR image to store real world luminance levels.

At this point, we obtain a situation that is identical to physically based rendering, i.e. real world luminance values stored in a high dynamic range (HDR) image file. Note, however, that this image file cannot be displayed “as-is” on screen, which leads us to the next step.

Step 2: Exposure Control: compress the wide range of luminance levels into a single, displayable image.

The display device must “compress” the physical luminance levels into something that a screen can support (i.e. 8 bit per channel) by transforming the data with an operation usually known as “Tone Mapping”, or “Exposure”.

In our example above, we obtain something like this:

1 For example, Adobe Photoshop CS2 and beyond provide “out of the box” tools to accomplish this task.


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HDR picture processed for display purposes with a Tone Mapper performing local adaptation based on contrast (Photoshop CS2).

Note however, that the result is very subjective. There is no “correct” answer. The important point to make is that the user is now able to control the image’s exposure as he wants, without being affected by the limitations of his camera. There is a huge gain in flexibility here.

We can see the brightest areas as well as the dimmest areas at once after using a digital exposure capable of adaptation in localized areas (Photoshop).


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Matching an HDR image with 3ds Max Exposure Control: real world luminance values

As you saw in the previous example, Camera Exposure can be done in software on top of an HDR image that recorded luminance levels of the real world. We will then see how this can be leveraged inside 3ds Max.

When using the “Physical Units (cd/m2)” option in the 3ds Max’s mr Photographic Exposure Control, the assumption is that background images also encode physical lighting units.

For example, if you photographed a sky that had an actual brightness of 2500 cd/m2, the 3ds Max exposure control would expect the image to be in a 0 to 2500 range for the RGB values.

A luminance meter is required to calibrate HDR images to real-world luminance values. Luminance meters can quantify luminance levels in cd/m2.

With this option, we can calibrate HDR background with the mr Photographic Exposure so Shutter Speed, Aperture and Film Speed values match values that would have been used with a real camera photographing the same sky!

When using this option, any data seen through the Camera is expected to be at a physical scale. This is also true for HDR backgrounds.


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Let’s assume this real-world scene where the brightest area (the sky) has a measured luminance of ~2500 cd m/2:

A rather “normal” picture….

Step 1: Assemble an HDR image from a series of LDR images:

This is done by taking several pictures of the same environment with a tripod, at various shutter speed settings:

A series of LDR images ready to be assembled in Photoshop or HDR shop

The luminance of this sky is at ~2500 cd / m2 in its brightest spot.

This number is obtained with a luminance meter.

My digital camera produced this result with the following exposure settings:

The image is saved as a low dynamic range format (JPG).


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Step 2: Normalize the HDR image to a range between 0 and 1.0:

The resulting HDR image from the previous step will most likely contain pixels that are set to arbitrary values which will cause us trouble later:

An HDR image loaded in HDR Shop shows that our sky (the small rectangle) reaches ~26 units. This is somewhat arbitrary

We need to normalize the HDR image to a range between 0 and 1.0 to keep things under control. This is done in HDR Shop with the Scale tool:

The scale tool allows changing pixel values of the image.

Here, we can see that image has somewhat arbitrary values. Our goal is to rescale the image so its brightest spot get close to 1.0

To get there, we rescale to a factor of 1/x. In our case, this is 1/26, which is ~0.385


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Step 3: Load the image in 3ds Max and define its scale

We now have an HDR image ranging from 0 to 1.0. Our goal is to scale it back up so 3ds Max interprets the sky portion of the image as if it has a brightness of 2500 cd/m2.

Load the image with a Gamma Correction value of 1.0 to keep it linear:

HDR Image loaded in linear space with a Gamma of 1.0

The HDR image plugin of max allows for converting to LDR on input. DO NOT enable this feature! Keep it as Real Pixels with the Def. Exposure ON.

Don’t miss this step! Failing to do so will introduce non linearity in the image, which is exactly what you want to avoid…

Don’t miss this step!

Failing to do so will introduce non linearity and re-scale the pixels to other values as well.


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Give it back a scale in the Output rollout:

The RGB Level of the Ouput rollout allows for scaling up or down pixels read from disk. Our goal is to bring it back to the measured luminance: 2500 cd /m2

Image rendered with the HDR picture as a background. The Photographic Exposure Control now works correctly with the HDR image. We have a calibrated environment.

This re-rendered image now has an identical brightness as the source LDR image.

Both HDR background and CG exposure now work according to physical values.

Relighting the scene with photometric lights is now made possible.

We now have a calibrated LINEAR COLOR SPACE


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Compositing with HDR images.

Overview

We will exploit the fact that light calculation implies an additive or multiplicative process by using the HDR pixels as lighting data on which we can perform math operations. In this section, we will explore ways to generate raw HDR data to re-assemble a finished image in a compositing package such as Photoshop or Composite.

This is made possible because 3ds Max can store luminance data in the same image formats used for HDRI photography. 3ds Max performs lighting calculation in LINEAR SPACE. This enables workflows where you can blend lighting effects from light banks and groups in real-time for artistic explorations of light colors and light levels.

3ds Max has the capabilities to render in full floating point precision (32 bit for Red, Green and Blue respectively).

Note how the pixel values can go beyond the 0-1 range.

Gotcha!

The main idea behind this process is to disable any Exposure Control that 3ds Max may have and perform this task in the 2D environment after our layers have been added together.

Keep in mind that we leave it up to the 2D application to reconstruct the final image. Therefore, we must maintain the integrity of the data into the image files we render to disk by:

Turning OFF exposure control so we keep the data in a non-altered way in the resulting files.

Saving our HDR images with Gamma Correction = 1.0 to maintain the data in a linear form.

Ignoring those criteria will produce unexpected results in the 2D compositing application, essentially due to incorrect mathematical equations.

3ds Max can render images that go beyond the 0-1 range. This is important to maintain physical accuracy of lighting calculations and an advantage we can leverage in floating point capable compositing applications.


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Light Blending Workflow Example

The basic procedure consists into rendering separately each group of lights (light banks) as HDR files. Those files are recombined in a compositing application capable of handling HDR images. Since light is additive by nature, it is only a matter of “adding” the rendered images together with the “linear add” blending mode. Tone Mapping (Exposure) is done at the end of the process, inside the 2D Application. Color correction can then be done on each layer individually.

Each light group is rendered individually, color corrected and added together. Camera Exposure is done at the very end.

Light Blending Workflow Example: interior rendering assembled with separate layers.

LED wall only, saved as LED Wall.hdr

Camera Exposure

Linear Add

Color Correction

Light Group C

Color Correction

Light Group B

Color Correction

Light Group A

Each layer is rendered separately. They are combined in a compositing application to reconstruct the final image. It is important to render images out as HDR formats otherwise, clamping and artifacts will occur.

It is also important to turn 3ds Max Exposure control OFF so we maintain the raw lighting data in a linear form (unaltered by the exposure control).


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Table Lights and Downlights only, saved asTable Lights and Downlights.hdr respectively.

All images assembled in Photoshop (32 bit image mode)

You can apply color and brightness changes on individual layers.

Light is additive. You need to use the LINEAR ADD blending mode to reconstruct the final image properly, so each layer is added with the others.

Exposure control is one at the END of the process, just like in real life, whether it is your eye or a camera.


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Combined effect: LED wall + Downlights + Table lights simply added together.

Color variations explored quickly in 2D by applying color correction on individual layers. No need to re-render the images!

With layered images, we can change the Hue and Intensity of each layer individually in real time!

The final image is still plausible since you only alter the underlying data and leave the exposure control at the very end of the process.

The final image shows that all layers are added on top of each other. HDR data saved in the images prevent clamping from occurring.

Because “adding” is a linear mathematical operation, we refer to this as the linear workflow.


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Another color variation…

(Model courtesy of Aksel Karcher - www.electricgobo.com and Autodesk)

http://www.electricgobo.com/

Documents

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