Map Features Overlays on a Cylindrical Projection |
Map Features Overlays on a Cylindrical Projection |
Feb 14 2012, 05:50 PM
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#16
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Member Group: Members Posts: 699 Joined: 3-December 04 From: Boulder, Colorado, USA Member No.: 117 |
There are a couple of other considerations as well. First is that I wrote a routine to convert the USGS label data in planetographic coordinates to my map that is in planetocentric. Actually the USGS maps (and presumably, feature coordinates) are really planetocentric, in that the coordinates of features on non-spherical moons are defined by the orientation of the direction to the body center rather than the direction of the local surface normal. The fine print explains that they are "planetographic relative to a spherical surface" or something like that. What they mean by "planetographic" is not that surface normals are used to define coordinates (they aren't), but that west longitudes are used (planetocentric coordinate systems traditionally use east longitudes). Very confusing- it took me a long time to sort this out myself. John |
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Feb 14 2012, 05:56 PM
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#17
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Member Group: Members Posts: 890 Joined: 18-November 08 Member No.: 4489 |
QUOTE Very confusing- it took me a long time to sort this out myself. no kidding same here , but i still have to look things up . |
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Feb 14 2012, 06:04 PM
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#18
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Senior Member Group: Members Posts: 1628 Joined: 5-March 05 From: Boulder, CO Member No.: 184 |
The fine print explains that they are "planetographic relative to a spherical surface" or something like that. What they mean by "planetographic" is not that surface normals are used to define coordinates (they aren't), but that west longitudes are used (planetocentric coordinate systems traditionally use east longitudes). Thanks much for the elucidation. Here is a link that looks to be consistent with this scenario: http://planetarynames.wr.usgs.gov/TargetCoordinates And here is the result when I refrain from doing the transformation: Steve -------------------- Steve [ my home page and planetary maps page ]
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Feb 15 2012, 07:37 PM
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#19
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Senior Member Group: Members Posts: 1628 Joined: 5-March 05 From: Boulder, CO Member No.: 184 |
-------------------- Steve [ my home page and planetary maps page ]
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Feb 15 2012, 08:47 PM
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#20
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Senior Member Group: Members Posts: 1628 Joined: 5-March 05 From: Boulder, CO Member No.: 184 |
And here is Europa with features larger than 40km. I'll have to consider whether to rotate the labels for some of the Linea:
-------------------- Steve [ my home page and planetary maps page ]
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Feb 15 2012, 09:18 PM
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#21
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Senior Member Group: Members Posts: 1628 Joined: 5-March 05 From: Boulder, CO Member No.: 184 |
-------------------- Steve [ my home page and planetary maps page ]
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Feb 18 2012, 08:12 PM
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#22
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Senior Member Group: Members Posts: 1628 Joined: 5-March 05 From: Boulder, CO Member No.: 184 |
Here's Iapetus, with a 5 degree shift that appears to reconcile the image with the IAU convention of the feature longitudes.
Other versions can be found here (for Iapetus along with other objects): http://laps.noaa.gov/albers/sos/features I just figured out how to select the fonts, so future revisions should have an improved look. -------------------- Steve [ my home page and planetary maps page ]
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Feb 29 2012, 02:00 PM
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#23
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Solar System Cartographer Group: Members Posts: 10151 Joined: 5-April 05 From: Canada Member No.: 227 |
A very nice project, Steve - I'm enjoying these maps.
Phil -------------------- ... because the Solar System ain't gonna map itself.
Also to be found posting similar content on https://mastodon.social/@PhilStooke Maps for download (free PD: https://upload.wikimedia.org/wikipedia/comm...Cartography.pdf NOTE: everything created by me which I post on UMSF is considered to be in the public domain (NOT CC, public domain) |
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Aug 18 2015, 11:33 PM
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#24
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Senior Member Group: Members Posts: 1628 Joined: 5-March 05 From: Boulder, CO Member No.: 184 |
Thanks Phil - now 3 years later, I'm checking now on improving my feature overlay for Vesta. Interesting that the USGS Gazetteer for Vesta seems to have longitudes about 150 degrees off. Claudia is supposed to be on the prime meridian for example, yet is listed as 146 longitude if I'm reading this correctly.
http://planetarynames.wr.usgs.gov/nomencla.../AdvancedSearch Does anyone know why there is a discrepancy on this? -------------------- Steve [ my home page and planetary maps page ]
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Aug 19 2015, 12:10 AM
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#25
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Member Group: Members Posts: 890 Joined: 18-November 08 Member No.: 4489 |
the mosaics here for Vesta line up almost perfectly with the 3d mesh
http://dawndata.igpp.ucla.edu/tw.jsp?section=data/FC/Maps but why the USA govt. and the rest of the world differ 0 to 360 and -180 to +180 that is not new QUOTE yet is listed as 146 longitude if I'm reading this correctly. that is however a bit odd ... |
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Aug 19 2015, 12:12 AM
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#26
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IMG to PNG GOD Group: Moderator Posts: 2250 Joined: 19-February 04 From: Near fire and ice Member No.: 38 |
There are/were several Vesta coordinate systems in use. I don't remember the details but needless to say this can be confusing.
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Aug 19 2015, 04:24 PM
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#27
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Administrator Group: Admin Posts: 5172 Joined: 4-August 05 From: Pasadena, CA, USA, Earth Member No.: 454 |
There are four different coordinate systems in use for Vesta. Some information in this blog post and more here.
-------------------- My website - My Patreon - @elakdawalla on Twitter - Please support unmannedspaceflight.com by donating here.
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