Surface Model TIN

7/31/2019 Surface Model TIN

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Create a new map document

1. Start ArcGIS.2. Create a new directory, M:\3d to store this lesson's data.3. Create a new map document, rather than opening an existing one. Save the document as

M:\3d\3d.mxd.

4. Enable the 3D Analyst and Spatial Analyst extensions from "Customize >Extensions..."


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5. Enable the 3D Analyst toolbar (Right click mouse from the meanu bar)


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Add surface model data layers to a data frame

View a TIN layer and alter its symbology

1. Rename the Layers data frame to TIN. (More information about TIN format:http://en.wikipedia.org/wiki/Triangulated_irregular_network)

2. Add the dem grid data source from the L:\packgis\forest directory.3. Add the pf_tin (TIN Data Source, on the CD in the L:\packgis\cfr250 directory). The Pf_tin

layer will load with random-colored breaklines, but with a green > red > white elevation filllegend. Zoom into the area shown by the red box below.


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4. Note the hard edges. Hard TIN edges for this data set are enforced by stream lines.

5. (NOTE: In MGH 044, since the map server is done and can not be fixed so far, ifyou can not run the "Symbology", just read through the exercise, but you can finish

your this lab exercise either in Suzzallo GIS lab or your own laptop or desktop.)

Open the symbology properties forPf_tin. Note there are two different feature typeslisted (Edge types and Elevation). The Symbology Function may not be able to

perform due to the lab computer issue, if you are running into the difficulties, just

read through it (till Step 15).


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6. With the Edge types features selected (note the difference between selected andchecked!), clickAdd All Values. TIN triangles are composed of a number of differentedge types. Adding all values will show all the edge types for the TIN. For more

information on TIN creation and breaklines, see ArcGIS 's on-line documentation.


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7. Now you see all the different edge types. Note that in some places the triangles are verysmall, whereas in other places the triangles are very large. Where the surface is more

convoluted there are more and smaller triangles, but where the surface is more simple, it

can be represented with fewer large triangles.

8. Select Elevation. Alter the number of classes to 32, select the green-yellow-red color ramp,and uncheck the Show hillshade checkbox.


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Now you can see more elevational variation. But without artificial hillshading it is difficult

to determine the form.

Recheck the Show hillshade checkbox to see the landform


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Do you see how shading makes a big difference in the appearance of surface models? Shading is

what allows the eye to interpret a surface as a 3-dimensional object.

9. Open the symbology properties again and click the Add button. There are severaladditional choices for how to render (display) the 3D TIN data.

10.Select Face aspect.... Aspect, or slope direction, is the compass bearing for each triangleface. Imagine if you dropped a bowling ball on a triangle edge and measured the compassangle of the ball's trajectory; this is the aspect value. And uncheck "Elevation".


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11.Do you see how the location circled below has triangles facing northwest? If you canimagine the erosional effect of a stream, this should make intuitive sense.


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12.Add another renderer (Properties > Symbology > Add). This time select Nodeelevation...

13.Alter the drawing order by selecting the Node elevation type and clicking thebutton.


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14.You can now see the individual vertices (nodes) that define each triangle.


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dem histogram

View the histogram from TIN elevation (open the Properties > Symbology > Classification

dialog for the TIN).


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The overall bimodal distribution is similar between the two data sets. But the data sources that

created the two different surface models are different.

You have just loaded and altered the legend properties for a TIN. Why do you think each triangle

appears with a single shade? What feature of the TIN model makes this so?

TINs are used in addition to grids as data sets representing surfaces. Certain surface modeling

and analysis functions in ArcGIS act only on TIN surfaces, and not on grid surfaces.


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Derive slope and aspect grids

Derive a degree slope grid

1. Zoom back out to full extent.2. Set the Geoprocessing > Environment > Raster Analysis and Cell Size to Same as

layer dem. Also, open the "Processing Extent" tab and assign it as Same as layer dem.

3. Select Spatial Analysis > Surface > Slope from ArcToolbox.4. Areas that are green are less steep; areas that are yellow to red are steeper.

Documents

Surface Model TIN