Mapping Hacks

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Chapter 2, Mapping Your Neighborhood

#20 Make 3-D Raytraced Terrain Models

HACK

To improve the highlights in the Landsat composite, we also add an addi-

tional light source to the top of our file, like so:

light_source { <100, 500, 10000> color <1,1,1> } // ambient light

Also, we want a realistic background for our terrain model, so we render a

clear blue sky in the background, by adding the following

sky_sphere sec-

tion to the end of our .pov file:

sky_sphere {

pigment {

gradient y

color_map {

[ 0.2 color <.5 .75 1> ]

[ 1.0 color <0 0 .5> ]

}

scale 2

translate -1

}

}

Finally, we rerun the rendering process as before. This time, it takes about

90 seconds on our machine, but the result, as shown in Figure 2-20, looks

pretty fantastic! The important thing is that the elevation model and the

image map need to have the same extents and be more or less in the same

projection in order to line up. If they don’t, you can use gdalwarp to trim

and/or reproject the elevation model to match the image map, so that they

do line up. Again, gdalwarp is covered in more detail in “Convert Geospa-

tial Data Between Different Formats”

[Hack #68].

Rendering Hand-Drawn Maps in 3-D

Of course, you don’t have to drape satellite imagery over a digital elevation

model. In particular, digital raster graphics (DRGs) of the USGS’s hand-

drawn topographic maps make great image maps for 3-D terrain.

Figure 2-21 shows an example ...