Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition

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 appear represent the cells ...