Exercise 4: Building a TIN to represent terrain
The town of Horse Cave, Kentucky, is situated above a cave that once served as the source of drinking water and hydroelectric power for the town. Unfortunately, the groundwater that flows in the cave was polluted by household and industrial waste dumped on the surface and washed into sinkholes. Dye-tracing studies and a three-dimensional survey of the cave revealed the relationship between the cave passages and the town and demonstrated the connection between open surface dump sites and contamination of the groundwater in the cave below.
Thanks to the development in 1989 of a new regional sewage facility and the joint efforts of the Cave Research Foundation and the American Cave Conservation Association (ACCA), the groundwater is cleaner, and the cave has been restored. It is now operated as a tour cave and educational site by the ACCA.
Cave data was provided courtesy of the ACCA.
Viewing the cave and the landscape
First, you will open the BuildTIN scene and view the cave survey and some terrain data layers. You’ll use this terrain data to create a TIN and drape some other layers on it to visualize the relationship of the cave to the town.
- Start ArcScene by clicking Start > All Programs > ArcGIS > ArcScene 10.
- On the ArcScene - Getting Started dialog box, click Existing Scenes --> Browse for more.
- Navigate to the Exercise4 folder and double-click the BuildTIN ArcScene document.
- Check the box to show the Cavesurvey layer.
- Right-click Cavesurvey and click Zoom To Layer.
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Creating a TIN from point data
You have a point layer called vipoints point. This coverage consists of points with an attribute called SPOT that contains elevation values taken at these points. You’ll create the TIN surface model from these points using the Create TIN geoprocessing tool.
When using geoprocessing tools, you will see a progress bar at the bottom of your document displaying the name of the currently executing tool. When the tool finishes executing, a pop-up notification will appear on the system tray. This is called background geoprocessing which, by default, is turned on when the software is installed and opened. To disable background geoprocessing, use the Geoprocessing Options dialog box from the Geoprocessing main menu.
- Click the Catalog tab to expand the Catalog window into the view.
- Scroll to find Toolboxes.
- Expand Toolboxes, click System Toolboxes, then choose the 3D Analyst Tools toolbox.
- Navigate to the TIN Management toolset and double-click the Create TIN geoprocessing tool.
- Click the Browse button to set the Output TIN location.
-
Click the Home
button, double-click the Terraindata folder, then change the output TIN name to tin1 and click Save.
- Click the Input Feature Class drop-down list and click vipoints point.
- Click OK.
- Right-click the tin1 layer in the table of contents and click Properties.
- Click the Symbology tab.
- Click the Add button to open up the Add Renderer dialog box.
- Click the Face Elevation with graduated color ramp option and click Add.
- Click Dismiss to close the Add Renderer dialog box and return to the Layer Properties dialog box.
- Switch off the original single color renderer by unchecking the Faces checkbox in the list of renderers.
- Click OK to close the Layer Properties dialog box.
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Adding features to a TIN
Now you will add hard and soft breaklines and a clip polygon to the TIN. You’ll add the railroad features as soft breaklines, so they’ll be represented on the surface but won’t influence the shape of the surface. You’ll add the brklines features as hard breaklines with elevation values to refine the shape of the surface in areas that you’re most interested in. Finally, you will add the smclp polygon as a soft clip polygon to more smoothly define the edge of the TIN.
- From the Catalog window, scroll to find Toolboxes.
- Expand Toolboxes, click System Toolboxes, then click the 3D Analyst Tools toolbox.
- Navigate to the TIN Management toolset and double-click the Edit TIN geoprocessing tool from the bottom window.
- Click the Input TIN drop-down list and click tin1.
- Click the Input Feature Class drop-down list and click railroad.
- Click the height_field drop-down arrow and click <None>.
- Click the SF_type drop-down arrow and click softline.
- Click the Input Feature Class drop-down list and click brklines.
- Click the Input Feature Class drop-down list and click smclp.
- Click the height_field drop-down arrow and click <None>.
- Click OK.
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After the next step, you will see that the railroad follows a bed that has been leveled somewhat relative to the surface.
Setting feature base heights from the TIN
Now you will set the base heights for the road and railroad features from the new TIN.
- Right-click roads and click Properties.
- Click the Base Heights tab.
- Click Floating on a custom surface.
- Click the drop-down arrow and click tin1.
- Click OK.
- Right-click railroad and click Properties.
- From the Base Heights tab, click Floating on a custom surface.
- Click OK.
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Setting raster base heights from the TIN
Including the aerial photo of the town in the scene makes the relationship between the cave and the town much more evident. You’ll drape the raster over the TIN and make it partly transparent so that you’ll be able to see the cave beneath the surface.
- Right-click photo.tif and click Properties.
- Click the Base Heights tab.
- Click Floating on a custom surface.
- Click the drop-down arrow and click tin1.
- Click the Display tab.
- Type 30 in the Transparency text box.
- Click OK.
- Check photo.tif in the table of contents so it becomes visible in the scene.
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Now the aerial photo is 30 percent transparent. You can see large patches of the TIN over the photo because the TIN and the photo have the same drawing priority. If you wanted the TIN to be visible below the photo, you could change its drawing priority to 10 (lowest) on the Rendering tab of the TIN's Layer Properties dialog box. You could also offset the base height of the TIN or the photo by a small amount.
Cleaning up the scene
To clean up the scene, you'll turn off the visibility of some layers that are no longer needed and make the cave line symbol larger.
- Uncheck vipoints point.
- Uncheck brklines.
- Uncheck tin1.
- Click the line symbol for the Cavesurvey layer.
- Type 5 in the Width box.
- Click OK.
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Creating a profile of the terrain
The cave follows the valley floor orientation. To get an understanding of the shape of the valley, you will create a profile across the TIN. To create a profile, you must first have a 3D line (feature or graphic). You will start ArcMap, add the TIN to the map, and digitize a line to make your profile.
- Start ArcMap by clicking Start > All Programs > ArcGIS > ArcMap 10.
-
On the ArcMap - Getting Started dialog box, select New Maps and then click Browse
to set the default geodatabase path to D:\3DAnalyst\3D_Default.gdb.
- Click OK to close the Getting Started dialog box.
- Click Customize, point to Toolbars, and click 3D Analyst.
- Click Customize and click Extensions.
- Check 3D Analyst if it's not already.
- Click Close.
- Open the Catalog window and navigate to the Exercise4\Terraindata folder in the Folder Connections path where you locally saved the tutorial data.
- Click the tin1 layer and drag it into the map view, then release the mouse button.
-
From the 3D Analyst toolbar, click the Interpolate Line
button.
- Click the upper-left corner of the TIN, drag the line to the lower-right corner, and double-click to stop digitizing.
-
Click the Profile Graph Tool
button.
- Right-click the Profile Graph Title bar and click Add to Layout.
- Close the Profile Graph window.
-
Click the Data View
button to return to data view.
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
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Creating a line of sight on the terrain
Another way of understanding the terrain is to create a line of sight. Lines of sight show what parts of a surface are visible and what parts are hidden along a line from an observer's point to a target point.
-
Click the Create Line of Sight
button.
- Type 2 in the Observer offset text box.
- Click on the south slope of the higher land in the upper right part of the TIN (the observer point), drag the line to the lower-right part, and release the mouse button (the target point).
- Close the Line Of Sight dialog box.
- Click Edit and click Select All Elements.
- Click Edit and click Copy.
- Switch back to ArcScene and click Edit, then click Paste.
-
Click the Save
button in ArcScene.
- Click File in ArcMap and click Exit.
- Click No to saving changes and close ArcMap.
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In this exercise, you learned how to create and work with a TIN surface model using ArcScene and ArcMap. You discovered how to construct and symbolize a TIN dataset to accurately represent a 3D surface. Breaklines and polygons were added to additionally depict surface features, such as railroads and terrain elevation values. Further surface analysis was then conducted using aerial photography as a draped raster layer on the TIN. Finally, you completed the exercise conducting 3D surface analysis on the TIN model using the interpolate line and create profile graph tools in ArcMap.
Now that you've learned how to represent a surface using a TIN model, you can begin to explore other areas of the ArcGIS 3D Analyst extension. In the next exercise, you will learn how to create and work with animations in ArcGlobe.