Form_vs_shape_1

8/8/2019 Form_vs_shape_1

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Form vs. Shape 1James Carruthers

RhinocerosNURBS modeling for Windows

Advanced 3D Modeling with3rd Edition


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2005 Hydraulic Design

Rhinoceros is a registered trademark of Robert McNeel & Associates


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Form vs. Shape 1

Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Getting Started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Basic Shapes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Logo Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Tunnel Edges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

Tunnel Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

Tunnel Alternate Patch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Tunnel Alternate Sweep1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Tunnel Alternate Sweep2 NetworkSrf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

Tunnel Alternate Point Editing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Refning Brim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48

Finishing Outer Shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Shelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77


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Form vs. Shape 1

GettingGettingGettingGetting StartedStartedStartedStarted

Choice of tolerance can have a big impact on how much trouble youre

going to run into with modeling and with downstream operations if

manufacturing is your goal. The tolerance chosen here, is quite "relaxed,"

to avoid unnecessary hassle.

1111.... Start a NewNewNewNew file

using the Millimeters

template

2222.... Open the

DocumentPropertiesDocumentPropertiesDocumentPropertiesDocumentPropertiesdialog.

3333.... On the Units page,

set the tolerance as

shown.

IntroductionIntroductionIntroductionIntroduction

The main theme of this tutorial is how there are

multiple solutions to any modeling challenge you

might encounter and evaluating the suitability of

different approaches depending on the purpose

of the model. Different techniques might be

used when modeling for manufacturing as

opposed to illustration, and different techniques

are more commonly used when Designing as

opposed to modeling. Theres more than one

way to skin a hat.

This is an advanced tutorial. It is intended to be

easy to follow, but the emphasis here is on what

NURBS and Rhinoceros can do, not necessarily

how to execute every command prompt-by-

prompt. The Evaluation version of Rhino includes

a number of basic tutorials to help you get

started. Commands are referred to by the name

used for typed entry and are HighlightedHighlightedHighlightedHighlighted .


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Form vs. Shape 1

Optimum meshing settings can vary greatly from project to project, even

for different objects in the same project. These settings make it easy to

drastically change the polygon count by adjusting just 2 values, Min edge

length and Max dist, edge to srf, and on this particular object do a good job

of capturing subtle surface contours with a low polygon count, albeit at the

expense of the accuracy of tiny details like fillets[illustrate]. Greater

accuracy would be required for STL output, but reducing the polygon count

in long skinny surfaces (like fillets) is key to improving the speed of your

shaded views.

4444.... Go to the Mesh

page, select Custom,

and try these settings.

You may want to

adjust them based on

yourhorsepower.

5555.... On the Grid page,

set these options.


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Form vs. Shape 1

7777.... In Rhino V3 SR4, on the WebBrowserWebBrowserWebBrowserWebBrowser page you can associate a web

page with a file that you can view in a browser window "on top" of Rhino.

To use this feature, enter the location of the tutorial index, which would be

"your_CD_drive_letter:\index.htm" and check the options as shown. The

next time you open the file, the tutorial will "pop up" in it's own window.

8888.... On the Modeling

Aids page, adjust the

nudging settings as

shown.

9999.... Exit the dialog.


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Form vs. Shape 1

BasicBasicBasicBasic ShapesShapesShapesShapes

2222.... Make another EllipsoidEllipsoidEllipsoidEllipsoid centered at world

coordinates ((((0000,,,,----1111,,,,0000)))). It's axis lengths are 11111111,,,,7777....5555,,,,

and 9999.... This is for the outer edge of the brim.

NomenclatureNomenclatureNomenclatureNomenclature

There are 4 main

features to this hard

hat that will be

referred to during this

tutorial.

1111.... Create an EllipsoidEllipsoidEllipsoidEllipsoid for the main surface with

axis lengths of 7777,,,,8888,,,, and 9999 units, centered about

the world origin.

Shell

Logo Panel

Brim

Tunnel

(0,-1,0)


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Form vs. Shape 1

3333.... In the Right view,

draw a CurveCurveCurveCurve of

Degree 3333 representing

the top of the outer

edge of the brim.

4444.... Make anotherCurveCurveCurveCurve for the bottom

edge of the brim.

It doesn't matter if

you pick the objects

to trim in a

perspective or side

view, when the curves

are flat that is what

determines the

direction of the trim.

5555.... Select the curves,

start TrimTrimTrimTrim, and trim

off the top and

bottom of the larger

ellipsoid.

(-3.5,1.0) (6.0,1.0) (11.0,1.0)

(-12.5,-1.5).

(-4.0,-0.5) (3.7,-0.5)

(11.6,-1.9)

(-12.3,-2.2).


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Form vs. Shape 1

6666.... TrimTrimTrimTrim the main

surface with the lower

curve, just for now.

7777.... HideHideHideHide the brim trim curves.

8888.... ExtrudeExtrudeExtrudeExtrude using the ToPointToPointToPointToPoint Mode, the edge of

the brim to a point 2mm above and 1mm head

of the centre point.

9999.... JoinJoinJoinJoin the extruded

surface to the outer

brim.

(-1,2)


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Form vs. Shape 1

LogoLogoLogoLogo PanelPanelPanelPanel

1111.... Draw a CurveCurveCurveCurve for

the profile of the logo

panel

2222.... ExtrudeCrvExtrudeCrvExtrudeCrvExtrudeCrv the curve in StraightStraightStraightStraight Mode using

the BothSides option by 5555 units.

3333.... DeleteDeleteDeleteDelete the curve just extruded.

4444.... Use ChangeDegreeChangeDegreeChangeDegreeChangeDegree on the logo panel surface

and raise it's Degree to 5555 in both directions.

5555.... Turn on its control points.

(-9.2,2.3)

(-9.6,-0.9)

(-8.2,5.2)


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Form vs. Shape 1

4444.... Nudge these points

back 2222....5555 units.

5555.... Nudge these points

forward 0000....5555 units.

6666.... Finish by nudging

these points back 0000....5555units.


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Form vs. Shape 1

7777.... Draw a CurveCurveCurveCurve for the front profile of the logo

panel

8888.... MirrorMirrorMirrorMirror the curve

about the Y axis.

9999.... JoinJoinJoinJoin the curve

halves.

9999.... JoinJoinJoinJoin the curve

halves.

10101010.... TrimTrimTrimTrim off the logo

panel surface.

(3.3,2.0)

(3.4,-1.0)

(2.5,5.0)(0,5.0)


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Form vs. Shape 1

Of course in this case it would have been just as

easy to draw a PlanePlanePlanePlane in a side view, but this is

one of those commands you may find handy

sometimes but not think of using.

11111111.... Draw a CutPlaneCutPlaneCutPlaneCutPlane through the logo panel

along the world Y axis.

13131313.... Select half of the

split panel and hit

CopyCopyCopyCopy.

12121212.... SplitSplitSplitSplit the logo

panel with the plane.


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Form vs. Shape 1

We did this little loop-d-loop because we're going

to work on a susequent surface in half and want

a single edge to snap to and use as a boundary.

It will be discarded later. I use this often to have

a copy of an object that gets changed and have

an alias to "!_CopyToClipboard _Undo _Paste."

The underscores let this alias work in non-

english versions of Rhino.

15151515.... PastePastePastePaste the half

panel surface.

14141414.... UndoUndoUndoUndo the splitting

operation.

16161616.... HideHideHideHide the full panel surface for now.

17171717.... DeleteDeleteDeleteDelete the CutPlane surface and the curve

used to trim the panel.


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Form vs. Shape 1

TunnelTunnelTunnelTunnel EdgesEdgesEdgesEdges

1111.... In the Top view, draw a CurveCurveCurveCurve of Degree 3333

that will describe the edge where the 'tunnel'

meets the main surface.

2222.... ProjectProjectProjectProject this curve onto the main surface and

check. Its fairly important that it match whats

here closely.

(2.0,0.0)

(2.0,-1.0)

(2.0,10.0)

(2.0,-5.2)

(3.8,-8.0)


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Form vs. Shape 1

3333.... HideHideHideHide the projected curve. We will refer to this

later as the 'tunnel edge curve.'

4444.... HideHideHideHide the brim polysurface.

5555.... Draw another

CurveCurveCurveCurve for the side

profile of the tunnel.

6666.... ExtrudeExtrudeExtrudeExtrude in StraightStraightStraightStraight Mode the side profile

curve a couple of units.

Constructing the tunnel surface tangent to this

edge will ensure that the mirrored halves of the

tunnel will be G2(curvature continuous)to each

other.

End Snap

(-6.8,6.6)

(-3.7, 8.5)(1.55,8.83)

(6.4,7.0)

(9.16,3.6)

(9.2,0.4)


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Form vs. Shape 1

7777.... Use ShowEdgesShowEdgesShowEdgesShowEdges with the All Edges option on

the main surface to find the seam of the original

ellipsoid. The Thick lines for edges and seams

option under the AdvancedDisplayAdvancedDisplayAdvancedDisplayAdvancedDisplay settings, used

for the screen shots in this tutorial, also shows

surface seams.Compare the position of the seam to the top

profile curve. If it looks like this, do step 8.

This was not a critical step in this situation, but

it can be a good idea to avoid the surprise down

the road of finding what you thought was one

edge is actually split across a surface seam.

8888.... If needed, MirrorMirrorMirrorMirror the main surface about the

world Y axis with the Copy option set to NoNoNoNo.

9999.... In the Top or Perspective view, TrimTrimTrimTrim the main

surface with the top profile curve.


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Form vs. Shape 1

13131313.... Draw a small CurveCurveCurveCurve, snapping between the

corner of the logo panel and the main surface.

Use the PlanarPlanarPlanarPlanar Osnap to place the middle point

approximately with the mouse.

10101010.... In the Side view,

draw a LineLineLineLine snapping

to the EndEndEndEnd of the side

profile curve and the

corner of the logo

panel.

11111111.... TrimTrimTrimTrim the bottom off the main surface with

the line in a side view.

12121212.... DeleteDeleteDeleteDelete the line.

End Snap

End Snap

End Snap

(3.54,-8.07)

End Snap


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Form vs. Shape 1

14141414.... Make another CurveCurveCurveCurve between the corners ofthe side profile surface and the main surface. To

place the middle point, hold SHIFT to use the

OrthoOrthoOrthoOrtho Osnap then you can place it by eye or use

the Grid Snap to place it close and nudge it.

(1.25,Y aligned with

first point)

End Snap

End Snap


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Form vs. Shape 1

You can probably visualize the sort of surface we

want to have within the area enclosed by these

edges and curves.

What makes this tricky is that it has 5 "sides"

and of course one of the basic properties and of

NURBS is that they are 4-sided. This means oneof two things: the surface will have to be

trimmed or it will have to be created with more

than one surface.

There are a number of ways to tackle a problem

like this, depending on the purpose of the model

and your design intent, which boils down to

what features--edges, dimensions, curves--are

'critical,' what's most precisely specified.

In this contrived example, weve decided that the

edges and curves around this surface are

critical, so we have to build a surface or

surfaces that fills in this hole, matching those

edges very accurately.

Well first use the technique I finally chose to

follow through given the hypothetical

requirements, then present a number of

alternate approaches that might come to

mind(not necessarily that would work, but which

you might think of trying)in this kind of situation.

Surface modeling seems to have its own version

of the Uncertainty Principle from quantum

mechanics. The more you try to nail down the

edges of a particular surface, the harder it is to

directly control the actual section of the surface,

and vice versa. And in general the more curves

you create to feed into the surface creation

commands, the better the chance youre going

to wind up with a mess.

15151515.... HideHideHideHide the top profile curve.


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Form vs. Shape 1

TunnelTunnelTunnelTunnel SurfaceSurfaceSurfaceSurface

1111.... In a side view,

draw a LineLineLineLine.

2222.... Use SplitEdgeSplitEdgeSplitEdgeSplitEdge the

edge of the side

profile surface at the

intersection of the

line using the IntIntIntInt

osnap.

3333.... Run SplitEdgeSplitEdgeSplitEdgeSplitEdge

again and split the

edge of the shell

where it intersects the

line in the Right view.

4444.... DeleteDeleteDeleteDelete the line

drawin in step 1.

(-8,5,7.5)

(-5.0,3.0)

Int snap

Int snap


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Form vs. Shape 1

The locations to split the edges were determined

pretty much by trial-and-error.

5555.... Build a surface with SweepSweepSweepSweep2222, matching

Tangency to the side profile surface. Use the DoDoDoDo

NotNotNotNot SimplifySimplifySimplifySimplify cross-section curve option.

6666.... Use SplitEdgeSplitEdgeSplitEdgeSplitEdge on

the edge of the label

face, splitting it about

where shown by eye.

Rail

Surface Edge

Match Tangency

Rail

Surface

Edge

Section

Curve


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Form vs. Shape 1

7777.... SweepSweepSweepSweep2222 again,

matching Curvature to

the end of the

previous sweep.

8888.... Create a NetworkSrfNetworkSrfNetworkSrfNetworkSrf, matching Curvature to

the end of the last sweep. Make sure to only

match Position to the other edges.

RailSurface Edge

Match Curvature

Rail

Surface

Edge

Surface

Edge

Surface Edge

Curvature Match

Curve

Surface

Edge

SectionCurve


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Form vs. Shape 1

The transitions between the surfaces look good--it may not appear perfectfrom every angle in the analysis modes, but it's sufficient for most real-

world purposes and certainly within the relatively 'relaxed' tolerance

settings.

There obviously is a problem within the Network surface. Without any

interior sections to tell NetworkSrfNetworkSrfNetworkSrfNetworkSrf what to do and only one edge

curvature constraint, thats what happens, plus Network surfaces tend to

sag between the sections.

It would certainly be possible to repair with with point-editing, but doing so

while maintaining continuity can be tedious.

9999.... Inspect what your

have built using ZebraZebraZebraZebra

and/or EmapEmapEmapEmap.

When I built this using the "Work In Progress"

version of Rhinoceros V4, the Network surfaceshown here actually turned out much better and

would require just minor point-editing.


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Form vs. Shape 1

13131313.... DeleteDeleteDeleteDelete the surface.

10101010.... UndoUndoUndoUndo or DeleteDeleteDeleteDelete the Network surface.

11111111.... Replace it with a SweepSweepSweepSweep2222 surface.

If we were to switch around the rails and the

sections, as at right, the result is cleaner, but

not what we are looking for because it does not

have continuity to the sweep.

12121212.... With ExtractIsocurveExtractIsocurveExtractIsocurveExtractIsocurve , get 2 curves from the

surface, one near the middle, one near the top.

Make sure the curve at the top is relatively

straight and smooth, showing no signs of the

ripple further down, we dont want to have to

adjust it.

Rail

Surface Edge

Match Curvature

Rail

Surface

Edge

Rail

Surface

Edge

Rail

Curve


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Form vs. Shape 1

15151515.... MoveMoveMoveMove the end point of the curve along the

edge of the shell using the NearNearNearNear snap until it's

approximately in line with the other wo points..

14141414.... DeleteDeleteDeleteDelete control

points from the

middle curve until

there are only 3.

16161616.... Tweak the middle point in the top view.


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Form vs. Shape 1

17171717.... Create a new NetworkSrfNetworkSrfNetworkSrfNetworkSrf including the 2

new interior section curves. Use the default

tolerances.

18181818.... HideHideHideHide the side profile surface.

19191919.... DeleteDeleteDeleteDelete the interior section curves.

The result should look something like this, much

improved.

Surface

Edge

Surface Edge

Curvature Match

Curve

Surface

Edge


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Form vs. Shape 1

22222222.... MirrorMirrorMirrorMirror the tunnel and shell surface along the

world Y axis.

23232323.... JoinJoinJoinJoin everything up.

24242424.... SaveSaveSaveSave your work up to now.

20202020.... HideHideHideHide the half logo panel surface.

21212121.... Use ShowSelectedShowSelectedShowSelectedShowSelected to retrieve the full logo

panel surface.


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Form vs. Shape 1

TunnelTunnelTunnelTunnel AlternateAlternateAlternateAlternate PatchPatchPatchPatch

1111.... SaveAsSaveAsSaveAsSaveAs under a new filename for working on

these variations.

2222.... ExtractSrfExtractSrfExtractSrfExtractSrf these surfaces.

3333.... DeleteDeleteDeleteDelete them.

4444.... HideHideHideHide the logo panel surface.

5555.... With ShowSelectedShowSelectedShowSelectedShowSelected , retrieve the half logo

panel and the side profile surface.

6666.... Use MergeEdgeMergeEdgeMergeEdgeMergeEdge to

repair the split in the

edge of the logo

panel.


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Form vs. Shape 1

This was done because we want the Patch

surface to be fitted Tangent to only two of the

edges.

7777.... JoinJoinJoinJoin, starting with the bottom curve and then

connecting the adjacent surface edges.

8888.... Fill in the hole with

a PatchPatchPatchPatch . The default

checkbox settings

with 15151515 or 20202020 Surface

U and V spans should

be fine.


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Form vs. Shape 1

Patch is not what I call a 'front-line' surface

creation tool. Outside the purposes for which its

intended(and you can see similar geometry used

in other applications,) such as filling in corners

where several fillets different sizes come

together(a situation for which a mathematically

"exact" NURBS solution does not exist)and

Now at first glance

this seems to look

fine, so what is the

problem?

A Patch can be used in a situation like this to

get a surface very quickly, but the result is

generally not feasible to tweak with point-editing

and not of superlative surface quality-a grid

pattern may become apparent in the surface

analysis views--or accuracy, as you can see with

the edge of a patch surface at right. Very dense

settings that slow down your whole model may

be necessary to get a patch within tolerance to

join.


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0

Form vs. Shape 1

TunnelTunnelTunnelTunnel AlternateAlternateAlternateAlternate SweepSweepSweepSweep1111

1111.... DeleteDeleteDeleteDelete the Patch

surface.

2222.... ExplodeExplodeExplodeExplode the curve

built for making the

Patch.

3333.... DeleteDeleteDeleteDelete the curves

that were created

from surface edges.

4444.... HideHideHideHide the remainingcurve.

5555.... ExplodeExplodeExplodeExplode the shell and tunnel polysurface.

6666.... DeleteDeleteDeleteDelete the tunnel surface.

7777.... Duplicate the shell surface using CopyCopyCopyCopy with

the InPlaceInPlaceInPlaceInPlace option.

8888.... HideHideHideHide one of the shell surfaces.9999.... UntrimUntrimUntrimUntrim the other shell surface with

KeepTrimObjects set to NoNoNoNo.


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Form vs. Shape 1

10101010.... Using

ShowSelectedShowSelectedShowSelectedShowSelected ,

retrieve the curve

used to trim off the

main surface and the

tunnel edge curve.

11111111.... TrimTrimTrimTrim off the

ellipsoid.

12121212.... DeleteDeleteDeleteDelete the trim

curve.

13131313.... Remove the split

in the edge of the

side profile surface

using MergeEdgeMergeEdgeMergeEdgeMergeEdge or

UntrimUntrimUntrimUntrim .


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Form vs. Shape 1

This is might be the first solution that wouldcome to mind when considering this problem.

While this may look like a good start, its not

really very promising considering what we want

to do. If we compare the tunnel edge curve to

the intersection of the sweep with the shell(curve

made with IntersectIntersectIntersectIntersect,) it's not really close.

It would be possible to add more section curves

to the sweep and/or point-edit to get closer but

it would take a lot of work.

14141414.... Build a Sweep1 along the side profile

surface. It doesn't affect the surface much, but

use the AlignAlignAlignAlign withwithwithwith SurfaceSurfaceSurfaceSurface option.

The plan to sidestep the 5-sided surface issue in

this case would be to edit the surface--I justnudged a couple points here--so that it gets

trimmed off by the the brim. That's great, but

again it does not lend itself to precisely aligning

with our 'critical' features.

Rail

Surface Edge

Section

Surface

Edge

Section

Curve


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Form vs. Shape 1

TunnelTunnelTunnelTunnel AlternateAlternateAlternateAlternate SweepSweepSweepSweep2222 NetworkSrfNetworkSrfNetworkSrfNetworkSrf

1111.... DeleteDeleteDeleteDelete the Sweep1

surface.

2222.... HideHideHideHide the brim

surface and the

tunnel edge curve.

3333.... Retrieve the half

brim surface with

ShowSelectedShowSelectedShowSelectedShowSelected .


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Form vs. Shape 1

4444.... Use DupEdgeDupEdgeDupEdgeDupEdge to

extract this curve

from the brim

surface.

4444.... Create a BlendBlendBlendBlend curve. Using CurvatureCurvatureCurvatureCurvature

Continuity, blend from the extracted curve then

(you can do this in either order) use the

Perpendicular option to blend to the edge of the

logo panel approximately where shown.

(2.78,209)


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Form vs. Shape 1

5555.... Turn on the control points for the Blend curve

and DeleteDeleteDeleteDelete two points.

There is an option in the Blend command to use

Position continuity, which accomplishes the

same thing as deleting these points, but this is

just as easy.

6666.... JoinJoinJoinJoin the Blend

curve to the extracted

edge curve.


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Form vs. Shape 1

7777.... Split the edge of

the logo panel with

SplitEdgeSplitEdgeSplitEdgeSplitEdge snapping to

the EndEndEndEnd of the curve.

8888.... Build a SweepSweepSweepSweep2222surface.

9999.... JoinJoinJoinJoin the shell and

Sweep2 surface.

End Snap

RailSurface Edge

Match Tangency

Rail

Curve

Section

Curve

Section

Surface

Edge


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Form vs. Shape 1

10101010.... Retrieve this

curve with

ShowSelectedShowSelectedShowSelectedShowSelected .

7777.... Fil in the hole with

a NetworkSrfNetworkSrfNetworkSrfNetworkSrf,

matching Curvature to

the end of the

Sweep2 surface. Only

match Position to the

other edges.

Surface

Edge

Surface Edge

Curvature Match

Curve

Surface

Edge


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Form vs. Shape 1

While it may be possible to salvage this, there

are a couple major issues.

With how a 2-rail sweep works, even though the

blend curve that's part of the one rail was

matched wihth G2 continuity, it's not quite

enough to avoid the creation of a visible change

in the surface. Now it should be possible to

tweak the curve and/or the surface to remove

that, and to help the 'fold' in the network

surface, but it would be hard to point-edit

without pulling the surface away from the brim

edge, and the level of fine-tuning this would

involve should only be neccessary when working

on something like a car body.

The biggest problem is that the geometry at this

corner of the network surface shown here is

what we technically refer to as nasty.' Stretching

the corner of a surface infinitely thin like this

can cause problems with fillets and booleans, it

will be challenging to make the seam with

adjacent surfaces invisible, and the slightest out-

of-tolerance curve or edge will prevent it from

joining to it's neigbors cleanly. Use with caution.


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Form vs. Shape 1

In my original project, this approach required

coming up with many section curves for network

surfaces and many iterations, and in the end I

didnt get a result that was better than close

enough, and here were not close at all. The

lesson from both these examples would seem to

be that building with fewer surfaces is not

necessarily simpler.

Here's an example of a similar attempt to make

this using two surfaces we will simply look at.

This was the kind of surface topology I actually

used in the project that inspired this, and what I

thought I was going to wind up doing in this

tutorial.Much like the previous example, SplitEdgeSplitEdgeSplitEdgeSplitEdge was

used on the tunnel edge and a SweepSweepSweepSweep2222 was

made. The remaining area was filled with a

NetworkSrfNetworkSrfNetworkSrfNetworkSrf, after making up one or two section

curves.


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Form vs. Shape 1

TunnelTunnelTunnelTunnel AlernateAlernateAlernateAlernate PointPointPointPoint EditingEditingEditingEditing

1111.... DeleteDeleteDeleteDelete the surface

created in the last

section, the brim

surface, everything

but these two

surfaces and one

curve.

2222.... ShowSelectedShowSelectedShowSelectedShowSelected the

full shell surface and

the tunnel edge curve.

3333.... With MergeEdgeMergeEdgeMergeEdgeMergeEdge

remove the split in the

edge of the half panel

surface.


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Form vs. Shape 1

4444.... SweepSweepSweepSweep1111 the edge of the side profile surface

along the edge of the logo panel. Use the default

settings.

This surface is much more promising than our

other attempts from a point-pushing potential

point of view. There are not too many points and

they are arranged in an orderly manner. The

back end folds over on itself, but what we want

in that area would be excessively painstaking to

achieve by point-pushing alone in any case.

Rail Surface

Edge

Section SurfaceEdge


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Form vs. Shape 1

6666.... Use SplitSplitSplitSplit with the Isocurve option, Shrink set to YesYesYesYes, to cut the sweep,

snapping to the previous point.

7777.... DeleteDeleteDeleteDelete the point.

5555.... Place a PointPointPointPoint in the

Right view.

This concept does not

actually require

accurately splitting

the surface , the

reference point is just

to help keep yourmodel identical to

this.

(-1.0,9.0)

Point Snap


45/79

Form vs. Shape 1

This macthing is necessary because Sweep1

does not try make the surface tangent to input

section edges.

8888.... DeleteDeleteDeleteDelete the back half of the sweep.

9999.... MatchSrfMatchSrfMatchSrfMatchSrf the swept surface to the side profile

surface. Specify TangencyTangencyTangencyTangency Continuity and Match

Edges by closest points.

10101010.... Turn on the control points of the frontsurface and begin editing it.


46/79

Form vs. Shape 1

There are no point-by-point instructions for

editing this surface primarily because they

would be rather tedious and not really help you

get the 'feel' of freeform editing. Here are

number of shots showing the progression over a

couple minutes of editing.


47/79

Form vs. Shape 1


48/79

Form vs. Shape 1

In a short time I was able to produce this

surface which has exactly the kind of form

desired and intersects the shell with an accuracy

to the reference curve of about 0.04 units. By

adding more knots to the surface it would be

quite possible to get it within our absolutetolerance settings of 0.01 units, but not

necessary for this exercise.

11111111.... Use IntersectIntersectIntersectIntersect on

the tunnel surface

and brim to obtain a

curve.

12121212.... Run CrvDeviationCrvDeviationCrvDeviationCrvDeviation on the intersection curve

and the tunnel edge curve to check the accuracy

of your editing. It will list and place points

highlighting the maximum and minimum

deviation. See if you can get within 0.05 units,

particularly near the top.


49/79

Form vs. Shape 1

Now this is not refined enough for machining

yet, but it looks pretty good. If the tolerance

requirements for the edge of the tunnel were

not too tight, this would be my preferred

approach to making this and a likely scenario

for when "designing" this object as opposed to

strictly producing a model.

Its generally easier and quicker to generate a

form by starting with some simple surfaces,

editing them until you like how they intersect,

and then trimming them up, than it is starting

with some edges and building surfaces to fill

them in. Now as the design gets more refined

and things get "nailed down," it might very well

wind up being rebuilt much like our original

version.

13131313.... To quickly obtain

a surface for the back

half of the tunnel

build a NetworkSrfNetworkSrfNetworkSrfNetworkSrf.

Curve

Surface Edge

Match Tangency

Curve

Surface Edge

Match Tangency


50/79

Form vs. Shape 1

RefiningRefiningRefiningRefining BrimBrimBrimBrim

1111.... OpenOpenOpenOpen the file you saved before working on thetunnel surface variations.

3333.... Draw a CurveCurveCurveCurve for the front section of the brim.

2222.... ShowSelectedShowSelectedShowSelectedShowSelected the brim polysurface.

(-12.24,-2.0)

(-10.34,-0.69)

(-11.61,-1.23)

(-11.77,-1.32)

(-12.06,-2.0)

(-11.85,-1.75)

(-8.45,-0.01)

(-12.24,-2.11) (-12.05,-2.14)

(-11.85,-2.0)

(-11.85,-2.14)

(-11.85,-1.44)


51/79

Form vs. Shape 1

4444.... MirrorMirrorMirrorMirror the curve

about the centre of

the base brim.

5555.... MoveMoveMoveMove the mirrored

curve up by 0000....53535353

units, or to the point

shown.

6666.... Point-edit the rear

section curve, leaving

the points near the

'lip' alone.

End Snap

(10.24,-1.58)

End point

(9.74,1.03)

(9.90,0.96)

(8.38,1.19)

(5.99,1.45)

(9.98,0.82)

(9.98,-0.39)


52/79

0

Form vs. Shape 1

7777.... Use DupEdgeDupEdgeDupEdgeDupEdge to make copies of the edges of

the base brim.

8888.... DeleteDeleteDeleteDelete the base brim. These steps were not

necessary, it's only to reduce clutter.

10101010.... Use the curves taken from the base brim as

the rails to build a SweepSweepSweepSweep2222 surface. Use the

Maintain Height option.

The Maintain Height option keeps the shape of

the lip from being scaled as the the distance

between the rail curves varies, as seen here. The

surface on the left was built with Maintain

Height off.

RailCurves

Section

Curve

Section

Curve


53/79

1

Form vs. Shape 1

While not an issue here, these small differencescan sometimes cause frustration with

subsequent operations, a boolean or fillet will

work on one side but not the other, which is why

you should generally build symmetric objects in

half and MirrorMirrorMirrorMirror them.

You will notice from the isocurves that the

surface is not totally symmetric. With any

operation where a curve or surface is "fitted,"

Rhino does not "know" that something is

supposed to be symmetric, it just iterates until

the result is within the tolerance settings. Therewere two such operations involved in this: the

sweep itself and the trimming of the base brim

from which the rail curves were extracted.

This has been built in an iterative manner suited

to working without construction history: quickly

build a starting shape, possibly use it to build

the shape a different way, then discard it.


54/79

Form vs. Shape 1

FinishingFinishingFinishingFinishing OuterOuterOuterOuter ShellShellShellShell

This edge would not fillet successfully with

FilletEdge. Where the fillet crosses the point

where the 3 surfaces meet, thats a case the

filleter doesnt know how to handle, so some

clean up would be required, although it's not a

huge problem.

1111.... ShowShowShowShow the main

shell polysurface.

2222.... HideHideHideHide the brim

objects.

3333.... Hide the offsetsurfaces.

4444.... DupEdgeDupEdgeDupEdgeDupEdge 2 edges.

5555.... JoinJoinJoinJoin them together.


55/79

Form vs. Shape 1

6666.... Create a PipePipePipePipe with

a Radius of 0000....3333

around the curve and

Cap set to NoNoNoNo.

7777.... The pipe shouldfully intersect the

shell already, but to

make sure use

ExtendSrfExtendSrfExtendSrfExtendSrf with the

Smooth option on

each end. Use a small

factor like 0000....2222.

8888.... MirrorMirrorMirrorMirror the pipe

about the origin.


56/79

Form vs. Shape 1

9999.... SplitSplitSplitSplit the shell with

the pipes.

10101010.... DeleteDeleteDeleteDelete the pipes,

the curve used to

build make them, and

the thin surfaces.

11111111.... Fill in the gaps with BlendSrfBlendSrfBlendSrfBlendSrf. Use CurvatureCurvatureCurvatureCurvature

Continuity and the default Blend Bulge settings.

You could build two blends or make one and

MirrorMirrorMirrorMirror it.


57/79

Form vs. Shape 1

12121212.... JoinJoinJoinJoin up the shell surfaces.

13131313.... ShowSelectedShowSelectedShowSelectedShowSelected the upper brim surface.

14141414.... Check that the surface normals on both

objects are pointed outwards. There are two

ways to do this. With DirDirDirDir, check the direction of

the arrows and use the Flip option as needed. Ifyou have to deal with a number of objects you

can use the AdvancedDisplayAdvancedDisplayAdvancedDisplayAdvancedDisplay settings to show

the backfaces (the "inside" direction) of all

objects in a separate color while working and

use the FlipFlipFlipFlip command as needed.

15151515.... BooleanUnionBooleanUnionBooleanUnionBooleanUnion the

brim and shell

objects.


58/79

Form vs. Shape 1

Booleans work on open surfaces and

polysurfaces with the normal directions

determining which side is out. If the normals

are pointing the wrong way, you will get an

opposite result to what you expect.

16161616.... In one FilletEdgeFilletEdgeFilletEdgeFilletEdge operation, put a 0000....125125125125

fillet between the brim and shell and around the

logo panel.


59/79

Form vs. Shape 1

ShellingShellingShellingShelling

Where the curvature of a surface is smaller than the thickness of the offset

it will fold over on itself, so some repairs will be required here. Doing small

fillets after shelling can help, but then repair is still needed because Rhino

V3 does not trim or extend offset surfaces to make a closed 'shell.'

1111.... OffsetSrfOffsetSrfOffsetSrfOffsetSrf the outer

polysurface by ----0000....2222

units, or ++++0000....2222 units,

depending on which

way the normals on

the surface are

pointing. Offset it to

the 'inside.' Use the

provided default

Tolerance.

We will first tackle

where the offset

surface has folded

over onto itself

around the lip.


60/79

Form vs. Shape 1

2222.... Use SplitSplitSplitSplit with the Isocurve option, and Shrink

set to YesYesYes Yes, to slice the lower surface below the

fold.

3333.... DeleteDeleteDeleteDelete the thin

piece.


61/79

Form vs. Shape 1

4444.... From the Top or Perspective view, run

ExtrudeCrvExtrudeCrvExtrudeCrvExtrudeCrv and extrude the edge of the upper

brim surface. Use the TaperedTaperedTaperedTapered Mode and specify

a DraftAngle of 4444 DegreesDegreesDegreesDegrees.

5555.... BlendSrfBlendSrfBlendSrfBlendSrf between

the lower brim and

the extruded surface.

Specify continuity as

shown and use the

default Blend Bulge

settings.

6666.... DeleteDeleteDeleteDelete the

extruded surface.

Tangency

Continuity

Curvature Continuity


62/79

0

Form vs. Shape 1

At the front, the surface has not quite folded

over, but there is a quite visible 'kink.' The

objective will be to remove the visible defect

without affecting the overall shape, not to

achieve any particular minimum radius. Now

this probably would have been best dealt with by

making the top and sides of the brim separate

objects, but these problems can't always beforeseen.

7777.... HideHideHideHide the outer

shell.

The next issue is further up the brim surface,

where it has again folded over on itself,

particularly at the back.


63/79

1

Form vs. Shape 1

8888.... Place 2 PointsPointsPointsPoints to snap to in the next split

operation. To make sure they are placed

correctly type them using world coordinates, so

enter wwww0000,,,, ----11111111....65656565,,,,----1111....53535353 and wwww6666....768768768768,,,,2222....5555,,,,0000....64646464.

9999.... Use SplitSplitSplitSplit with the Isocurve option, and Shrink

set to YesYesYes Yes, to slice the brim surface in two

places. Use the PointPointPointPoint Osnap and snap to the

points drawn previously.

(w0,-11.65,-1.53)

(w6.768,2.5,0.64)

Point snap

Point snap


64/79

Form vs. Shape 1

10101010.... DeleteDeleteDeleteDelete the points.

11111111.... In the Top view draw a LineLineLineLine along the world

X axis and another along the Y axis. Length is

not important, just that they cross the brim.

12121212.... ProjectProjectProjectProject thoselines onto the narrow

strip split out of the

brim.

13131313.... DeleteDeleteDeleteDelete the lines.


65/79

Form vs. Shape 1

14141414.... Point-edit the curves made by projecting to remove the self-

intersection. Your curves may not look exactly like these, so take these

pictures as general guidelines. Below is the rear curve.

15151515.... Point-edit the side curves. Do both separately or modify one and Mirror

it, though for our purposes it's not imperative that they be identical.


66/79

Form vs. Shape 1

16161616.... In this situation the tolerance in the ProjectProjectProjectProject actually eliminated the

kink in the front curve, here I just adjusted a point to make it fit the

original edge closer.


surface split from the

brim.


67/79

Form vs. Shape 1

18181818.... Use those 4 curves as sections to build a SweepSweepSweepSweep2222 surface between the

brim pieces. Match TangencyTangencyTangencyTangency to the rail edges and specify to Refit the

cross-section curves within 0000....01010101 units.

19191919.... DeleteDeleteDeleteDelete the curves used to build the sweep.

20202020.... Around the edge of the logo panel are 6

skinny surfaces, offset fillet surfaces that have

flipped over on themselves. DeleteDeleteDeleteDelete them.


68/79

Form vs. Shape 1

The final area to clean up is around the logo

panel and tunnel surfaces. The logo panel and

tunnel surfaces need to be trimmed off, and the

fillets repaired.

21212121.... JoinJoinJoinJoin together 4

tunnel surfaces.


69/79

Form vs. Shape 1

22222222.... Create a curve by running IntersectIntersectIntersectIntersect on the

logo panel and tunnel objects.

23232323.... Build a PipePipePipePipe witha Radius of 0000....125125125125

around the

intersection curve.


intersection curve.


70/79

Form vs. Shape 1

25252525.... Run ExtendSrfExtendSrfExtendSrfExtendSrf

with the Smooth

option on each end.

Use a small factor of

0000....15151515.

26262626.... SplitSplitSplitSplit the logo

panel and tunnel

objects with the pipe.


71/79

Form vs. Shape 1

27272727.... DeleteDeleteDeleteDelete the pipe

and thin surfaces.

18181818.... Use SplitSplitSplitSplit with the Isocurve option, Shrink set

to YesYesYes Yes, to split the fillet surface below the logo

panel, snapping to the EndEndEndEnd of the logo panel

edge.

29292929.... SplitSplitSplitSplit by Isocurve again, splitting the fillet

surface below the tunnel surface, snapping to

the EndEndEndEnd of the tunnel surface edge.

30303030.... DeleteDeleteDeleteDelete the small pieces.

End Snap

End Snap


72/79

0

Form vs. Shape 1

31313131.... Repeat the SplitSplitSplitSplit

and DeleteDeleteDeleteDelete operations

on the other side.

32323232.... UnTrimUnTrimUnTrimUnTrim the brim surface with the

KeepTrimObjects option.


73/79

1

Form vs. Shape 1

33333333.... On each side of the model, SplitSplitSplitSplit the curve with the Point option,

snapping to the End of the fillet surfaces.

34343434.... DeleteDeleteDeleteDelete the small curve pieces.

A lot of these steps are being done on both sides of the model separately

so that any small differences from one side to the other don't prevent this

from joining up successfully.

35353535.... Again on each side of the model, build a BlendBlendBlendBlend curve between the

edges of the fillet surfaces. Specify TangencyTangencyTangencyTangency Continuity.


74/79

Form vs. Shape 1

36363636.... JoinJoinJoinJoin the blend

curves to the pieces

of the brim trim curve.

37373737.... TrimTrimTrimTrim off the brim

surface.

38383838.... DeleteDeleteDeleteDelete the trim

curve.

39393939.... JoinJoinJoinJoin up all the

objects.


75/79

Form vs. Shape 1

40404040.... BlendSrfBlendSrfBlendSrfBlendSrf between the logo panel and tunnel

edges. Specify TangencyTangencyTangencyTangency Continuity.

41414141.... Run ExtendSrfExtendSrfExtendSrfExtendSrf

with the Smooth

option on each end of

the blend. Use a

factor of 0000....1111.


76/79

Form vs. Shape 1

42424242.... Draw a LineLineLineLine

between the ends of

the fillets.

43434343.... In the Right view,use the line to TrimTrimTrimTrim

off both ends of the

blend surface.

44444444.... DeleteDeleteDeleteDelete the line.

45454545.... JoinJoinJoinJoin the blend

surface to the

polysurface.

End SnapEnd Snap


77/79

Form vs. Shape 1

46464646.... Fill in each remaining hole with a small NetworkSrfNetworkSrfNetworkSrfNetworkSrf. Specify TangencyTangencyTangencyTangency

Continuityfor all edges.

47474747.... JoinJoinJoinJoin the network surfaces to the polysurface.


78/79

Form vs. Shape 1

48484848.... ShowSelectedShowSelectedShowSelectedShowSelected the

outer polysurface.

49494949.... JoinJoinJoinJoin the inner and

outer polysurfaces.


79/79

Form vs. Shape 1

Index

A

AdvancedDisplay 15, 55

Align with Surface 32

B

Blend 34, 71

BlendSrf 54, 59, 73

BooleanUnion 55

brim 5

C

ChangeDegree 8

CrvDeviation 46

Curve 6, 8, 10, 13, 14, 16, 48

CutPlane 11

D

design intent 18

Dir 55

DocumentProperties 2

DupEdge 34, 50, 52

E

Ellipsoid 5

Emap 22

Explode 30

ExtendSrf 53, 68, 73

ExtractIsocurve 23

ExtractSrf 27

freeform editing 44

G

G2 14

grid options 3

I

InPlace 30

Intersect 32, 46, 67

Int snap 19

iterative 51

J

Join 7, 10, 26, 35, 36, 52, 66, 72,

74, 75, 76

L

Line 16, 19, 62

Logo Panel 8

logo panel 5

M

Maintain Height 50

MatchSrf 43

MergeEdge 27, 31, 40

mesh options 3

Mirror 10, 15, 26, 49, 53, 54

modeling aids 4

Move 49

N

Near snap 24

NetworkSrf 21 22 25 37 39

Patch 28

Pipe 53, 67

Planar Osnap 16

Plane 11

Project 13, 62, 64

S

shell 5, 57

ShowEdges 15

Split 11, 42, 54, 58, 61, 68, 69,

71

SplitEdge 19, 20, 36, 39

Sweep1 32, 41

Sweep2 20, 21, 36, 39, 50, 65

symmetric objects 51

T

Tapered 59

tolerance 2, 64

ToPoint 7

Trim 6, 7, 10, 15, 16, 31, 72, 74

tunnel 5

Tunnel Edges 13

U

units 2

UnTrim 30, 31, 70

W

WebBrowser 4

Z

Documents

Form_vs_shape_1