PDA

View Full Version : Change a Map's projection via GIMP?



acrsome
12-01-2013, 04:46 PM
Howdy, all. First post. I found this site a few days ago and I'm just coming up for air. This place is a bit daunting. I spent a lot of time duplicating (or trying to duplicate) RobA's "realistic" mapping technique with GIMP. I played around with Linux for a few years so I know a little about GIMP but, wow, if there is one thing I have learned it is that my kung-fu is weak…

Anyway, I'm working on a map of a terraformed Venus. I found some great USGS 300ppi jpeg topo maps of the planet that date from 1997. Probably dated, but it's the best I can find; most maps I've found aren't really topo- instead they're radar reflectivity. There is Magellan data out there that goes down to a resolution of 75m, but I think that's a bit overkill, not to mention I'd probably need commercial mapping software to handle it.

So I stitched these six topo maps together into one beast of a 10800 x 27600 pixel map covering from 57N to 57S, thus excluding the poles. To put that in context, that's a 92" x 36" poster at 300ppi. (Actually, that size leaves some transparent 'slop' around the edges of the printed map area- the map is a bit smaller.) It's in mercator projection, and I'd like to change that to something else, maybe like a Winkel tripel. (Or Mollweide, Eckert, or Robinson- you know what I'm getting at.) Primarily, I'd like to do this so that I can use one reasonably-accurate scale, rather than changing it depending upon latitude. I'm going to use this beast for my own reference, as a sort of "big picture" and to plot a history, and then make smaller regional maps based upon it.

Is there a way to engineer such a change in GIMP?

jbgibson
12-08-2013, 01:20 AM
Check an app called G.Projector, from NASA. It does projection morphing, and very nicely. Plus, it's a free download.

Oh, and welcome to the Guild. Can't wait to see your Venus!

acrsome
12-08-2013, 08:34 PM
I found mention of G. Projector on another thread, and got excited, and downloaded it, but then I read that it requires equirectangular projection as input, not Mercator. Bummer. I guess I can live with Mercator.

The Venus map may well take years. I have a demanding day job. :)