Well the real globe has actual textures (I haven't applied them because they cause terrible performance for some mysterious reason)
Yeah, totally forgot about them. In fact, I've been having a bit of a look at textures tonight, I can't seem to render them. They either don't draw anything, or crashes in the Surface::getPixel with _surface->pixels = 0x00000000. Odd.
Enabling the poor texture rendering is an exercise in horror and shock and possibly frustration, but here goes:
1. Go to the Globe::draw function in Globe.cpp.
2. Comment out the filledPolygonColor(...) line and uncomment the texturedPolygon(...) line.
(if you're having fun you can also uncomment the polygonColor(...) line instead and see the globe in wireframe-o-vision!)
This would be enough, but because of how SDL works, surfaces need to be locked for pixel-level access and unlocked for blitting. So you also need to:
3. Comment out the lock() and unlock() lines so the blitting works.
4. Comment out the whole "base markers" drawing since anything with getPixel/setPixel will probably crash now since the surface is unlocked.
5. Comment out everything in Globe::blit except the Surface::blit(...) line so it doesn't redraw itself every few ticks (I'll optimize this eventually).
After all this you should have successfully revealed the beast:
Any attempt at rotation will take seconds and the textures don't even match the terrain and there's gaps in the polygons and oh gawd it's just so horrible that I just commented it out to never see the light of day while I cried in a corner for weeks and weeks
(seriously though with the huge performance problem there's no point in fixing the rest so I just moved on).
The main reason I was looking was if there were different light levels per texture, but interestingly not, so you'd have to update the texture as your blitting it. Should make things a little more interesting. Either that, or as you read in TEXTURE.DAT, you create several SurfaceSets with the modified palettes to give your different light levels, then you can just blit from whichever source you need.
Yeah palette wizardry is very common in X-Com, and since colors go from light to dark in the palette, you would just shift the palette a bit to the left for each polygon to make it darker. In OpenXcom you can achieve a similar effect with the Surface::offset function.
There are no ocean polygons (except in TFTD) stored in the game files. If I had to guess, the game might just generate a bunch of "ocean quads" itself that scroll horizontally along the flat map depending on the time, and get mapped as a "semi-sphere" on the globe. Or they use some wizardry involving circles or something, what do I know? 
If it were me, I'd probably create a hardcoded full sphere polygon list (landscape can draw over the top), but this way you could texture the sea too if you wanted.
Yeah that would be the more sensible option today, but those were
different times with only 32K of memory that you couldn't afford to waste or something who knows.
Plus it makes the day/night effect look smoother over the ocean.
