Map Globe IDL code

IDL program that remaps CED projected images into foldable globe maps

posted July 2001

Here is the tar file (2.3 MB) containing the IDL source code, some test programs and an example input image.

This IDL program implements the projection described in: 'An Equal-area Map Projection for Polyhedral Globes' by John P Snyder in Cartographica vol 29 no 1 spring 1992 pp 10-21. The tar file contains the idl program files and a test input data file. The program still has several problems:

- it takes a very long time to run for reasonable size output

- the input files must be in a CED simple projection, the place to add spherical rotations in commented in make_poly_map.pro

- the remapping is nearest neighbor, so it works best if the input image size is similar to the output image size. Once again the place to change this is commented in make_poly_map.pro

- there is still some minor? problem in the implementation of iterative adjustment step, the problem shows up as narrow gaps between the polygons in large output images

- the 'north globe' option only works for certain ranges of the deg_poly_lat, deg_ced_lat and deg_trap_lat input parameters

- i'm sure other problems still exist, but i have too many other things to work on to make this program nicer

Here are some example maps generated with the program:

This is the 'north globe' polyhedron projection that was made to Bill North's specifications. The dataset is simply land elevation colored with red as the highest elevations and blue as the lowest (the image has some flaws near the Himalayas and Andes that show up as anomalous white areas) The 'north globe' option in the IDL program allows the user to vary the number of panels circling the globe and also vary the latitude extent covered by each of the bands of polygons.

larger jpeg, 0.6 MB

This is the 'Dodecahedron' output image. The dataset for this image is from http://visibleearth.nasa.gov/cgi-bin/viewrecord?6889.

larger jpeg, 0.5 MB

This is the 'Icosahedron' output image. The dataset for this image is from http://visibleearth.nasa.gov/cgi-bin/viewrecord?8273.

larger jpeg, 0.4 MB

This is the 'Truncated Icosahedron' output image. The dataset for this image is from http://visibleearth.nasa.gov/cgi-bin/viewrecord?7650.

larger jpeg, 0.9 MB