View Full Version : Rectangular to circle

01-05-2011, 09:34 AM
Hi guys!
I can faintly remember that this question has already been asked, but I can't remember the result.
How can I transform two halves of a rectangular map to two hemispheres - similar to some maps in the recent December challenge?

01-05-2011, 10:04 AM
That would be useful. I think someone else was looking for an automated way of transforming regular rectangular maps to various other types of projections. If anyone has something like that, it would be a great resource.

01-05-2011, 11:04 AM
Yeah, it should be someplace we can find it too :)

01-05-2011, 03:38 PM
Blatant self-promotion:
Put the two halves of the map together and then import into Fractal Terrains from ProFantasy. The input can then be displayed in many, many different types of projections.

hugin, g-projector, flex projector, Generic Mapping Tools, and many other products will do this sort of thing.

01-05-2011, 09:04 PM
Are you familiar with projections?

If you have a map in a known cylindrical projection (One which produces a rectangular map), you just need to reproject each hemisphere into an Equatorial Azimuthal projection. In particular I'd recommend Stereographic Azimuthal. There is plenty of software that can do this including GDAL, QuantumGIS, and Hugin.

If you just drew an arbitrary map on a rectangular canvas with no regard to it being a representation of a sphere, you are pretty much screwed in terms of getting results that look good and make sense without reworking the map significantly.

01-11-2011, 11:42 AM
A good place to start is http://en.wikipedia.org/wiki/Cartographic_projection Wikipedia. Read up on how projections work. It's also fun to check out various galleries online which showcase different kinds of projections.

Most computer programs that deal with projections (that I've used: g-projector, Flex Projector, Hugin has it as one of its projections) use as their base map a map in the Equirectangular, plate carree projection, which is very simple to compute (on computers). G-projector is the easiest to use, and now that it's upped its maximum output to 3000x1500 pixels it's much more useful.

01-11-2011, 02:11 PM
The Flexify 2 (by flaming pear) plugin for photoshop (which will actually also work in gimp, the preview is just kinda fubar so you have to know what you want to do) will also do this along with hugin/etc. that others have mentioned. I usually use hugin for projection-switching, but flexify is really nice for especially this particular transformation; it's very user-friendly.

01-12-2011, 02:36 AM
There seems to be a number of useful programs. I have to check out some of them. Thank you all for your advice.