Martian Cartography |
Martian Cartography |
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Member ![]() ![]() ![]() Group: Members Posts: 147 Joined: 14-April 06 From: Berlin Member No.: 744 ![]() |
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/ -------------------- |
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#2
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Member ![]() ![]() ![]() Group: Members Posts: 248 Joined: 25-February 21 From: Waltham, Massachussetts, U.S.A. Member No.: 8974 ![]() |
https://pds-imaging.jpl.nasa.gov/data/msl/M...CES_PDS_SIS.PDF
section 3.9.2 has a discussion on easting which I think provides a start of an explanation: " These “easting” meters at a given latitude are related to true meters at the equator by the simple formula: map_meters = true_meters / cos(φ) where φ is the planetocentric latitude. " [ hey, one can use html entities in the forum ♥ https://www.w3schools.com/html/html_symbols.asp ] It looks like the provided meters are true meters (at the equator) and the projected easting has map meters since: 4590298.31635 = 4354494.086 / cos(18.4446271 degrees) This is getting closer to 4590877.824, with still ca. 580m of a difference. The gdal computed easting assumes a sphere with a radius of 3396190 m. Perhaps the reported true meter easting takes into account a local radius because these are also listed in the geojson, in the radius field. The gdal computed easting and northing is consistent with the simple formulas given in section 4.4.2.4: " planetocentric_latitude: Latitude of the point, measured using a planetocentric system. Planetocentric coordinates are measured as angles from the center of the planet. Latitude (φ_pc) is computed from northing (x) using the formula: φ_pc = x / Re • 180 / PI where Re is the ellipsoid radius, or 3396190 meters. longitude: Longitude of the point. Longitude is computed from easting (y) using the formula: θ = y / Re • 180 / PI " [ This is good and so simple that I can probably directly plot the traverse geojson on my equirectangular basemap ]. Since the northing matches, Re is 3396190 m. In addition to the correction to true meters from map meters easting, something else seems to be done to the easting. But what ? -------------------- --
Andreas Plesch, andreasplesch at gmail dot com |
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