Generating maps from images with MMPS

Take an image, eg. the one of Europa at:

Convert to ppm format and use mogrify to trim down:

mogrify -format ppm EuropaBall.jpg
mogrify -fuzz 20% -trim EuropaBall.ppm

Now do an inverse rectilinear transform, using the -i projection parameter:

project rectilinear -w 1000 -h 500 -i -f EuropaBall.ppm > europamap.ppm

Now we have an (incomplete) map of Europa:

Europa Map

We can then use this in the usual way:

project rectilinear -long 60 -w 500 -h 500 -f europamap.ppm > europa1.ppm

Europa view 1

project perspective -long -60 -lat -30 -w 500 -h 500 -f europamap.ppm > europa2.ppm

Europa view 2

Of course, only the mapped part of the moon appears.

One partial map may be used as a background to another:

project rectilinear -long 180 -w 1000 -h 500 -i -back europamap.ppm -f EuropaBall.ppm > europamap2.ppm

Double Europa Map

leaving only a few holes to be filled in (of course, the two maps may be generated from different images).

Photographs really are perspective views, so we can use the inverse perspective map too, but this requires knowing or working out the correct viewpoint and scaling factor to use. The -x parameter specifies the distance from the centre of the object (in object radii) and the -scale parameter specifies the overall magnification of the input image from the default. For a square image filled by the image of the object, the ratio of -x to -scale will be approximately 5.7, slightly more for small values of -x due to foreshortening. The -bg parameter may be used to specify a different background for the map image to aid correct scaling.

project perspective -x 5.76 -w 1000 -h 500 -i -f EuropaBall.ppm | display
project perspective -x 11.4 -scale 2 -w 1000 -h 500 -i -f EuropaBall.ppm | display
project perspective -x 100 -bg 255:0:0 -scale 17.6 -w 1000 -h 500 -i -f EuropaBall.ppm | display&

For space images, taken from a relatively large distance, the rectilinear transformation should give reasonably good results (for x distance greater than about 20, the difference with the perspective projection will be small).