The Third Spatial Dimension - Introducing Geographic Information Systems with ArcGIS - page 557

FIGURE 9-10
appear represent the cells of the DEM that can be seen from the positions on the river by
people on the boat at the points where GPS readings were taken. This isn't much use until
we add some additional graphical information. Here you may experiment. Start by adding the
cole_doq. In the T/C, drag it below the viewshed layer and zoom to the layer. Unfortunately, the
viewshed blots out the details of the imagery. Let's try various levels of transparency in the
viewshed layer (Layer Properties > Display). Maybe 80% to start with. Notice that some of the
water plant is visible but most is hidden from the GPS points on the river. See Figure 9-10. Now
experiment with different colors and transparencies of From_the_Boat.
57. Turn off the viewshed and cole_doq. Add cole_dem to the map. Add cole_drg to the map. Zoom
to the GPS track. Pan the map to the east so that it covers the area shown in Figure 9-11.
Find the Hillshade (3D Analyst) tool. Where is it? ___________________. Start the tool. For the
input surface choose cole_dem. Note that the default has the light source coming from 315
degrees (northwest) and at an angle above the horizon of 45 degrees. Call the resulting raster
Hillshade_1 and put it into 3-D.gdb. Leave everything the same. Click OK.
Once this process completes, a Hillshade of cole_dem should appear at the top of the Table
of Contents and a grayscale raster will appear. Note that everything is pretty bright except the
southeast-facing slopes of the river gorge.
58. Rerun Hillshade (being careful to specify cole_dem), lowering the sun altitude to 30 degrees
above the horizon and shifting the sun so it comes from the southeast (135 degrees). Call
the resulting raster Hillshade_2. Note the reduced amount of light everywhere and the deeper
shadows. Pick a color scheme that shows the sunniest spots as yellow, using the invert box
in the Symbology window. Notice how the steep, southeast facing slopes of the river canyon
are lit up with yellow. Look at the DEM, the DRG, and the output of Hillshade_2, adjusting the
transparencies so the image looks something like Figure 9-11.