Mapping Hacks

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Chapter 2, Mapping Your Neighborhood

#20 Make 3-D Raytraced Terrain Models

HACK

file to use as a height field, with simple parameters that control its display.

Once we’ve done that, we can drape satellite or aerial imagery over the ray-

traced terrain model, to give it a realistic look. The only really tricky bits are

getting the digital elevation models into an image format that POV-Ray likes

and orienting the satellite imagery so that it matches the underlying height

field.

Getting the Terrain Data

We picked Crater Lake, a lake formed in the caldera of an enormous and

ancient volcano in Oregon, to render in our example, because it’s a very dis-

tinctive-looking terrain feature. If you’re in the U.S., you can get data from

the USGS Seamless Data Distribution System

[Hack #67] at http://seamless.usgs.

gov/. We elected to download both the 1" National Elevation Data (NED) as

well as the Landsat composite imagery for the area surrounding Crater Lake.

Then we drew a box around the lake on the map using the area-download

tool, and we were given a pop-up window allowing us to download both

files. Make sure that the border of your download selection box stays green!

If you’re outside the United States, SRTM data for the whole world at 90m

resolution is theoretically available from NASA, as well as ground imagery,

including Landsat and MODIS data. The Global Land Cover Facility at http:

//glcf.umiacs.umd.edu/ ...