Hack 34. Map Other Planets

Explore the celestial spheres (and spheroids) with standard GIS tools.

The universe is a big place, perhaps the biggest.

Kurt Vonnegut

NASA's recent missions to other planets in our solar system have had a substantial mapping component, notably the Venus Magellan and the Mars Pathfinder missions. Mars and Venus, our nearest neighbors, have the best coverage of extraterrestrial imagery and GIS data available on the Web. However, the best Solar System mapping resources on the Web don't come directly from NASA. Many promising links to older data sets now return 404 Not Found errors, and their mission homepages feature lots of media-friendly space imagery and "For Kids" sections. For the hard work of planetary cartography, NASA collaborates with the astrogeology department at the U.S. Geological Survey, http://astrogeology.usgs.gov/.

3.14.1. Making Flat Maps of Other Planets

Visit the USGS Astrogeology FTP site at ftp://ftpflag.wr.usgs.gov/dist/pigpen/ for a mother lode of other-planetary GIS data on Mars, Venus, our moon, and Jupiter's moons. The FTP site ftp://webgis.wr.usgs.gov/mars/usgs/topo/MOLA_contours_25Mscale/Mars_MOLA_contours_colorimages.zip contains a great selection of vectors and rasters for making topographical maps of Mars. Many files give instructions for ArcExplorer, but the open source GIS products featured in this book are more than apt for the task. Additionally, you can get lots of nice data from the USGS Map-A-Planet site at http://pdsmaps.wr.usgs.gov/.

Quantum GIS [Hack #64], is a great basic viewer for extraterrestrial GIS data. Figure 3-41 shows an Equirectangular projection map displayed in Quantum GIS, zoomed in to Olympus Mons and Pavonis Mons, with overlaid topographical shapefiles from the same data set.

Figure 3-41. Raster map of Mars with overlaid topo vectors

Many extraterrestrial maps available on the Web use the visually familiar technique of hypsographic tintingfeatures shaded in an attractive, earthly scheme showing lowest altitudes in marine blue, and mountain peaks in a burnt-out yellow. This coloring scheme lends Earth maps a pleasing "natural look"; seeing other planets drawn with hypsographic tints reveals the attractive illusion for what it is.

3.14.2. Rendering 3-D Imagery of Other Planets

Raster maps in cylindrical projections are also suitable for use with xplanet, the 3-D planet renderer covered in [Hack #46] . xplanet was designed for rendering images of planetary surfaces and is a really good place to get started in this area. You can find code, images, and sample configurations at http://xplanet.sf.net/. A good compendium of planetary maps available online in cylindrical projections can be found at http://www.johnstonsarchive.net/spaceart/planetcylmaps.html.

The same cylindrical projection maps are perfect for rendering planets in POV-Ray, free raytracing software [Hack #20] . Using data from the Viking missions, available at http://solarviews.com/eng/homepage.htm, we rendered a 3-D image of Mars with the following .pov file:

camera { location <0, 0, -2.5> look_at <.01, 0, 0> } light_source { <3,0,-5> color <1,1,1> } sphere { <0,0,0>, 1 pigment { image_map { jpeg "marscyl1l.jpg" map_type 1 } } normal { bump_map { png "marscyl2.png" map_type 1 bump_size 10 } } finish { ambient 0.1 diffuse 1 specular 0.2 roughness .2 } rotate <0,180,-25> }

The core of this rendering is the sphere section, which provides the shape of the planet. The image_map section specifies the appearance of the surface, with the map_type of 1 causing the JPEG to be wrapped around the sphere. The bump_map section provides the elevation data, with the bump_size parameter emphasizing the terrain for visual effect. (We had to use the convert tool from ImageMagick to turn the original TIFF height field into a PNG. For reasons unknown, POV-Ray didn't care for the TIFF.) Finally, the rendering of Mars is rotated around to show the Valles Marineris and the Tharsis volcanos, and is tilted to reflect the planet's actual rotational tilt. The rendering is shown in Figure 3-42.

Figure 3-42. The Valles Marineris and the Tharsis volcanos of Mars, rendered in POV-Ray

Finally, if you're a fan of Manifold [Hack #65] , an excellent and inexpensive commercial GIS package, you'll be pleased to know that it, too, offers 3-D surfaces for all the planets in the Solar System; Mars and Earth are modeled as spheroids, and the other planetary bodies are modeled as spheres.

3.14.3. Other Otherworldly Resources

NASA's Solar System Simulator (http://maps.jpl.nasa.gov/) has a fine selection of non-GIS maps for all the bodies in our solar system that have been closely inspected.

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