Question about changing projections in Wilbur

[MrBragg]

I'm new to this whole mapmaking thing (and the forums!) and ran into a question I'm hoping you all can help me out with. Hopefully this all makes sense, but I've been trying to figure out how to take a large equirectangular world map, export a small region of it for working on details with relatively little distortion, and then reimport that region / reproject it back to equirectangular so it can be reintegrated into the large map. Using a map of Earth to practice, I could successfully take the equirectangular projection, use Wilbur to convert that to an orthographic projection centered on Iceland (a place with lots of distortion in the equirectangular map), and export the much less distorted regional map of Iceland. Where I ran into trouble was on the reverse step of getting Iceland back to equirectangular...

I could open the regional map up in Wilbur and set the latitude and longitude limits to their values for the regional map. My problem is that when I try to project this as an equirectangular projection, the output is a blank screen. Things seem ok if I choose orthographic and the map shows up roughly as expected, but I can't for the life of me get equirectangular to work. Is what I'm doing possible and I'm just messing something up? Or is this whole approach wrong?

[Vigilus]

Sounds like a great question, any answers?

[waldronate]

Except in a very few places, Wilbur has no notion of "projection". Everything in Wilbur is a flat plane for computational purposes except in a few areas of the program, and those are usually pretty explicit about putting the terms "projection", "latitude", and/or "longitude" in the UI. If you create an image of an area using the Map Projection window, then Wilbur will have no concept that it's anything other than a flat map when you reimport it. Putting map edges onto a map in the wrong projection won't change the projection of the map. You need to use an external tool to reproject the image to a consistent base. The projection that happens to satisfy the "everything at right angles and x=longitude, y-latitude" relationship between a sphere and a plane is called "Plate Caree", which is a special case of "Equirectangular" where the X and Y scales are the same. http://www.fracterra.com/ReprojectImage.zip is a simple tool that can reproject something back to an Equirectangular projection (with some pretty severe limitations).

The likely reason that it's hard to find something on the Map Projection window when it's a small part of the world is that the scaling is off and the area is offscreen. Try dragging the map view around with the mouse until you see the area of your map. The controls on that window are pretty twitchy and upside-down, but you'll get there eventually (if you're still trying after all of this time).

[MrBragg]

I realize I'm a month late here, and five months after my original question, but I ended up finding a workable solution with MMPS (http://www.users.globalnet.co.uk/~arcus/mmps/). I've been able to convert freely between equirectangular and pretty much anything else I've wanted (and vice versa!) using this little program, so it works for what I needed.

[acrosome]

G.Projector works also, and is free from NASA. It has a limited maximum size for the map, though.