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Map Features Overlays on a Cylindrical Projection
john_s
post Feb 14 2012, 05:50 PM
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QUOTE (scalbers @ Feb 14 2012, 09:33 AM) *
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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JohnVV
post Feb 14 2012, 05:56 PM
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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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scalbers
post Feb 14 2012, 06:04 PM
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QUOTE (john_s @ Feb 14 2012, 05:50 PM) *
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:

Attached Image


Steve


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scalbers
post Feb 15 2012, 07:37 PM
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Next one - here's what I have so far for Io showing all features larger than 150km:

Attached Image


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scalbers
post Feb 15 2012, 08:47 PM
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And here is Europa with features larger than 40km. I'll have to consider whether to rotate the labels for some of the Linea:

Attached Image


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scalbers
post Feb 15 2012, 09:18 PM
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And back at Saturn, here are the Mimas features (all available ones from the USGS Gazeteer):

Attached Image


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scalbers
post Feb 18 2012, 08:12 PM
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Here's Iapetus, with a 5 degree shift that appears to reconcile the image with the IAU convention of the feature longitudes.

Attached Image


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.


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Phil Stooke
post Feb 29 2012, 02:00 PM
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A very nice project, Steve - I'm enjoying these maps.

Phil



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... because the Solar System ain't gonna map itself.
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