The amount of polygons the original games load is hardcoded, but TFTD loads more then UFO. I converted the UFO textures to TFTD's palette and hauled the map across. I wrote a program to distribute the remaining polys UFO doesn't use in an even grid across the surface of the world to cover the ocean.
I didn't bother trying to line them up with the "ground" polys - those simply sit on top of the "ocean" polys. I suppose you might run into a potential problem with this method in that OpenXcom would need to check which poly missions are going to be performed in, in reverse order to that in which it renders them, for this to work.
Later kyrub found the value in the TFTD EXE that controlled how many polys were loaded, so I was able to crank it way up and make the ocean polys smaller (and hence more numerous, making the globe look a bit smoother).
Anyway, techno-mumbo-jumbo aside, for Mars you'd probably be best off starting with the whole-world-covering-poly-grid first then cutting holes in that to add in the terrain features such as the ice caps or whatever. Easiest way would be to grab the first 648 polys (12,960 bytes) from my combined world map and use them as a starting base, and I'd assume Volutar's editor and my texture converter can help you sort out the rest.
