Martian Cartography Options

[karolp]

I have recently freaked out a little bit about Martian maps of all sorts. And finally I was astonished with those highly detailed beauties that I list below. Nonetheless. some of them have huge inconsistencies (crater names) easily noticed when we compare the surroundings of Gusev crater. Enjoy:

http://www.ralphaeschliman.com/
http://planetologia.elte.hu/1cikkeke.phtml...arsmapinte.html
http://pubs.usgs.gov/imap/i2782/

[Andreas Plesch]

Another way to look at it is to assume that the reported easting is from a equirectangular projection with a standard latitude not at the equator but close to the landing site. In fact, one can back out the standard latitude because the easting and the corresponding longitude are given:

arccos(4354494.086 / 4590877.824) is 18.4663 degrees for the standard latitude possibly used.

If this is the case all the waypoints should use the same standard latitude. Here is the table with the standard latitude computed for all waypoints:

CODE

sol easting northing lon lat Re easting at 0 lat. standard lat.
0 4354494.086 1093299.695 77.45088572 18.44462715 3396190 4590877.824 18.46629998
14 4354497.517 1093294.73 77.45094676 18.44454339 3396190 4590881.442 18.46630001
15 4354502.424 1093329.801 77.45103403 18.44513505 3396190 4590886.615 18.46629999
16 4354528.468 1093338.387 77.45149727 18.4452799 3396190 4590914.073 18.46630002
20 4354548.64 1093330.59 77.45185605 18.44514836 3396190 4590935.34 18.4663

And, in fact all waypoints do use the same standard latitude. The only question is why this particular latitude. Perhaps that was the original target. A little farther north, closer to the delta, would make sense.

The center of the landing ellipse seems very close.

The average of the ellipse latitudes is 18.46630439 (after not double counting the repeated start and end).

Close enough for me.

So I think the M20 localization uses an equirectangular projection with a standard latitude at 18.4663 degrees N. The reported easting is based on this projection.

[edit] Ah, thanks, Mark. That completely confirms it.