1. In more ways than one, the success of your entire project is riding upon the quality of your DEM. Let's start by looking at the island DEM we've been working with. Open the Flyby project if you don't already have it open. Open the planimetric camera View Preferences to the Terrain page and check the Terrain Polygon Edges box.

2. Activate the plan view, hold the spacebar down, and click the Scale button or use the S key to enter scale or zoom mode. Click and drag up to zoom in and you'll see a wireframe representation of the 3D terrain surface. It's a grid of regularly spaced georeferenced points, each with an elevation.

3. Go to the Database Editor, select the island DEM, and move to the Extents page. The grid size is about 10 m by 10 m. 10-meter DEMs are sometimes referred to as having a 10-meter resolution. At render time grid cells are divided into triangular polygons. The degree of polygon subdivision is determined by the Maximum Fractal Depth value.

4. What can WCS import as terrain? As we saw earlier, the Import Wizard section of the Interactive Reference Manual lists the data types we can import as well as parameter suggestions for importing them. The written manual also lists data types that can be imported. We're going to import the most common format. Visit the 3D Nature web site for sources of these and other terrain data types.

5. USGS terrain data has long been the staple of landscape animators. The DEMs are free for download and have good resolution, usually 10- or 30-meter. This is adequate for most applications. The most recent incarnation of the USGS data type is the SDTS format. There are 2 rules to keep in mind when importing USGS data. First, you can't mix 10- and 30-meter data for import; pick one or the other. Second, and even more important, all SDTS DEMs must be imported at the same time. That's because the DEMs don't match across boundaries and WCS has to fix them during the import process.

6. The DEMs we're going to import are from Yellowstone National Park and will be used for the following sections. Here's a helpful tip for downloading USGS SDTS DEMs. You will find them by USGS topo quad name but the download filename will be an unintelligible series of numbers and letters. Save them under their quad name to make it easier to identify them later, but leave the .tar.gz extension so WinZip can recognize them in their tarred and gzipped format.

7. Go to the dem folder on the Tutorial 1 CD where you'll find Mount Jackson, Madison Junction, Lower Geyser Basin, and Buffalo Meadows tar.gz files. These are the compressed files as you'd download them, renamed according to quad.

8. We need to uncompress the files before importing them, so copy them to temporary space on your hard drive. Before extracting the files, open WinZip, and go to the Options > Configuration > Miscellaneous page. Deselect the TAR file smart CR/LF conversion option that is set by default. It has a way of corrupting DEM files, so make sure your WinZip isn't doing it. Once that's taken care of, ungzip and untar the terrain files to their own folders on your hard drive. That will make them easier to identify and prevent overwriting other files by the same name. For each DEM, you'll end up with 18 DDF files and a Readme.

9. Now we're ready to import the data into WCS. Create a new project and name it YNP.

10. Import data when asked.

11.Make your way to your unzipped DEM folders. If you have problems with the extraction process, you can use the uncompressed files saved in their respective folders on the Tutorial 1 CD. It doesn't matter which order we use, so I'll just start with the first one, Buffalo Meadows.

12. Select any of the DDF files and Open.

13. When asked if you'd like to Import more SDTS DEMs from another directory, answer Yes and choose any DDF from the Lower Geyser Basin folder.

14. Repeat the process to load the Madison Junction and Mount Jackson files. Answer No to the Import SDTS DEM question box after loading the last of the files.

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