GPS for Dummies.pdf - Engineering Surveyor

260Part III: Digital Mapping on Your ComputerWith a 3-D map, instead of relying on contour lines to understand the terrain,the land features jump out at you and are immediately obvious. Professionalmap users such as surveyors, land managers, and public safety officials use 3-Dmaps in addition to 2-D maps because they provide a different perspective whenlooking at landforms. With a 3-D map, it’s also much easier to show what theterrain is really like to someone who’s unfamiliar with reading contour maps.Discovering 3DEM Capabilities3DEM allows you to visualize terrain in three dimensions. Its name is a play onwords, referring to three-dimensional as well as Digital Elevation Model (DEM),which is the data the program uses to create maps. With 3DEM, you can Create and save 3-D maps based on elevation data. Change the view and perspective of 3-D maps. Overlay topographic maps on top of 3-D images. Identify coordinates on maps.Developer Richard Horne made the program straightforward and easy to use.It’s fast because it uses the SGI/Microsoft OpenGL libraries for image rendering.Time to put 3DEM to work. In the following sections, I use 3DEM to create somethree-dimensional maps. If you want to follow along with the examples, pointyour Web browser to www.visualizationsoftware.com/3dem.html anddownload 3DEM.You might be wondering why the program icon associated with 3DEM is a pairof sunglasses with one red lens and one blue lens. 3DEM has an option to displayimages that look even more three-dimensional if you’re wearing special3-D glasses with red and blue lenses. (Yup, just like cheesy movies such asthat 50s horror classic, House of Wax, where you wear the same kind of glasses,and it looks like Vincent Price is jumping out of the screen at you.) If you don’thave a pair of 3-D glasses lying around the office, visit www.3dglassesonline.com where you can get a pair for the price of a self-addressed envelope andpostage.Using DEM Data to Create a MapThe first step in using 3DEM is to load a DEM file. DEM (Digital ElevationModel) is a file format that contains elevation data. DEM files are producedby the United States Geological Survey (USGS) and cover most all land areasin the U.S. Frugal mapmakers can retrieve free DEM files from many sites onthe Internet.