[GRASS-user] Planet coordinate systems?

Hamish hamish_b at yahoo.com
Wed Sep 15 23:52:34 EDT 2010

On Wed, 8/25/10, Adam wrote:
> I am interested if anyone has used GRASS with data from Mars, or any
> other non-earth based system?  I don't see any epsg codes that would
> apply.  

EPSG is the European Petroleum Survey Group, so unless they find lots of
hydrocarbons on Mars I don't think EPSG's database will help much.

> So, I am looking for some general ideas and guidance to get going.

I'd suggest starting grass in text mode 'grass64 -text' or the Tcl/Tk
startup GUI (grass64 -tcltk) and following the text box method of
defining a new location. You can put in whatever terms you like for
defining the ellipsoid (radius of planet, sphere or ellipse terms), etc.
Nothing in the projection library is hardcoded for Earth AFAIK, other
bodies should be fine if you know the radius, etc. I don't know what
other planets/moons have had ellipse terms determined for them. Mars and
the Moon should be fairly well gravity mapped by this point. Perhaps the
Sun and gas giants have either very smooth geoids or ones that wobble
too much to define easily??

> If anyone has used GRASS this way, please let me know about
> your experience, useful links, or other things that might be
> helpful to deal with some of the existing planetary data,
> and how to use it.

You might search the mailing list for mention of Mars from ~ 3-4 years
ago. We added support for 0-360 deg longitude as that was what the
planetary scientists wanted to use instead of -180 to +180, etc.

but it's pretty easy to define a custom location by terms, and that should
give you all the control you need.

In GRASSNews volume 1 (or 3?) I think there's an article I wrote which
mentions details for importing Mars MOLA dataset.

keep looking up,


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