(2020-07-26, 16:09)Magnus Forsberg Wrote: I have no idea of what I'm doing but this works, sort of.
I used, and adapted the example from Travis below.
Something breaks around the northpole.
One problem with spherical mapping is that things go bad at the north and south poles. This isn't a problem on the bottom due to the fact that there's nothing at the south pole, but two polygons on top share the north pole as one of their vertices.
Another problem is that your image needs to be quite a bit taller than it currently is to work as a mercator projection. It seems like the image you have is roughly -80 to +80 latitude. If you change the the second 180 to 160 in the !TEXMAP line to reflect this, things get a bit better, but still not perfect (at least in LDView). I need to check to see if there is a bug in LDView. The top edge of the texture doesn't work well. Having said that, there is no way to apply two separate textures to the same geometry, so having a texture stop in the middle of a polygon leaves the rest of that polygon blank, and there's nothing you can do about that.
If the sphere geometry stopped at +80 degrees, and then a cone was used above that, a separate texture could be applied to the cone from above, and things would probably look pretty good. (Getting that texture to line up would take some work, but it would certainly be possible.) In that case, your existing texture would work great with a 160 degree vertical span.
I also tested by resizing your original image to be 1600 pixels tall, and just filling in the new space with the tan background (leaving the angle in the file set to 180). That actually improves things a lot, but the longitude lines then stop before the pole, and extending them up runs into the north pole discontinuity problem again.
As for the wiggly lines, I think that is caused by the fact that the spherical geometry is so low-resolution.