The Third Spatial Dimension - Introducing Geographic Information Systems with ArcGIS - page 556

FIGURE 9-9
Open the attribute table of Mtn_Retreat.shp. Note that two new fields have been added to the
table. What is the Volume of material that must be considered? _______________________ to
the nearest cubic foot. (Put commas in, even though the software didn't.) Sarea indicates the
number of square feet obtained by summing up the areas of all the triangles above the 1020
plane. Look at Figure 9-9.
Other Neat Stuff You Can Do with 3D Analyst: Viewshed
and Hillshade
Suppose that you are interested in knowing what part of the Coletown landscape you can see from the
river. ArcMap can calculate a “viewshed” that will graphically portray that information. Basically, you can
select a set of points, and the software will show you all the surface area that can be seen from one or
more of them. In our case, we will use the points from the GPS track to look at areas on cole_dem.
55. Add Boat_SP83 from ___IGIS-Arc\River. Make the size 2 and the color bright red. Find Viewshed
(3D Analyst) (Where is it? ________________.) Make the Input surface cole_dem. The observer
points should be Boat_SP83. Make the result a raster called From_the_Boat and place it in the
File Geodatabase that you made earlier: 3-D.gdb. The raster will be added to the map. Click
OK. Wait. The percentage of the calculation that is complete may show up at the bottom of
the screen as a blue bar. Realize that ArcMap is calculating a ray from each point in the GPS
track to each 100 by 100 foot square in the entire Coletown DEM. If your computer is slow you
probably have time to hand-calculate how many such pixels there are in the 6.7 mile by 8.6 mile
TIN. Or you could just go get some coffee.
56. The Viewshed of From_the_Boat will appear in the Table of Contents. Change the Not Visible
area to hollow or no color. Change the Visible area to a blue-green. The colored squares that