Map Features Overlays on a Cylindrical Projection Options

[john_s]

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

[JohnVV]

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 .

[scalbers]

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

[scalbers]

Next one - here's what I have so far for Io showing all features larger than 150km:

[scalbers]

And here is Europa with features larger than 40km. I'll have to consider whether to rotate the labels for some of the Linea:

[scalbers]

And back at Saturn, here are the Mimas features (all available ones from the USGS Gazeteer):

[scalbers]

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.

[Phil Stooke]

A very nice project, Steve - I'm enjoying these maps.

Phil