View Full Version : Projections

12-21-2010, 07:44 AM
I tried searching for this and couldn't find it, so apologies if this is rehashing old territory.

What are the best tools for creating projections?
Say I work on a traditional "flat" map, how can I take that image and turn it into a projection?

... and do these tools run on Mac Os? :P

12-21-2010, 09:04 AM
And just to answer my own post, in case anyone else is looking for projection tools,

I found this:

Which is pretty useful! And runs on Windows, Linux, and Mac os.

12-21-2010, 09:43 AM
Well the way you are phrasing your question seems to indicate a misunderstanding.

It's not a matter of "turning a flat map into a projection" (to paraphrase you) It's a matter of converting a map from one projection to another.

A projection is a way of turning the 3D points of a planet's surface into a flat map. In mathematics it's something we call a 'function'. And each projection is a different function that flattens the points onto the map in a different way. So we don't say a map 'is a projection' but rather it 'has a projection' which is a description of how it relates to the surface of the Earth (or whatever else it' might be a map of)

Every projection of a curved planetary surface causes distortion though the particular distortion varies. In particular, no such projection preserves distance (Some preserve some distances, but none preserve all distances.) Even a map that's lumpy and distorted has a lumpy and distorted projection function, though we don't know what that function is.

So whatever your 'flat map' is, it has a projection. Assuming you know what that projection is, you can convert it to other projections using special software ranging from one off little utilities, to full on GIS Suites.

But if you just want to know the projection and get the technical details right, and don't care about changing it to other projections, you just need to pick one that suits the map (Of course now I'm assuming you are drawing a fictional map from scratch now and don't have any other maps or data you need to stay consistent with). It's best if you do this before you start designing it but you can pick one to make it work after the fact, at least usually.

So before going into detail, which of these are you after, if either?

12-21-2010, 10:21 AM
What Hai-Etlik says is true. However, for relatively local maps (say, a couple hundred miles across or less), the projection effects are minimal for an Earth-sized world. After you determine where on a globe they should go, you can then distort them approximately using something like Photoshop to get them roughly into place. Unless you're dealing with large numbers of mostly-polar maps, most folks won't notice when you do this sort of thing. If you're aiming for atlas-style maps or have multiiple overlapping source material then things will get a little harder.

As tolcreator pointed out, gprojector is a good tool for reprojecting images.

Many years ago I wrote a toy called ReprojectImage ( http://www.ridgenet.net/~jslayton/ReprojectImage.zip ) to let me convert pieces of images into straight UV textures suitable for mapping onto spheres in various projections. It's a Windows-only toy, however. I have used it with moderate success to warp disparate map chunks into a single projection that then gets assembled in Photoshop.

12-21-2010, 10:42 AM
Yeah what I meant to say was:
"I want to turn an equirectangular map into... not an equirectangular map"

I've only ever drawn equirectangular maps before, either because the map I was drawing was of a planar world, I was drawing a small enough area of one, or I just didn't care.

12-21-2010, 11:14 AM
don't know what program youre planning on using, but if you just want the effect and aren't going for accuracy then you can use the Spherize feature in photoshop. Filter > Distort > Spherize. don't know what the command would be if you use GIMP.

12-21-2010, 01:06 PM
don't know what program youre planning on using, but if you just want the effect and aren't going for accuracy then you can use the Spherize feature in photoshop. Filter > Distort > Spherize. don't know what the command would be if you use GIMP.

For completeness, the Gimp version is Map to Object: http://docs.gimp.org/2.6/en/plug-in-map-object.html

-Rob A>

12-21-2010, 01:22 PM
Flex Projector (http://www.flexprojector.com/) is pretty good, too. It doesn't have as many projections as g.projector, but it can project vector art and you can make your own wild projections. Unless you have a pretty good understanding of the math and theory of projections you're unlikely to come up with anything too terrible useful, but it's fun and you might even come up with something [i]attractive[/] like Robinson did.

12-21-2010, 02:00 PM
My program of choice would be Hugin, which I believe also has a mac version. There's also a tuturiol for using Hugin somewhere on this site, though I don't have a link handy. I'm sure there's quite a few newer projections missing, but you've got all your typical bases covered with mercator projections, stereographic, equal area azimuthal, sinusoidal, orthographic, etc.

Edit: Found the Hugin tut: http://www.cartographersguild.com/showthread.php?5025-Hirez-map-projection-conversion-using-Hugin&highlight=hugin