Double Post!
For a while I’ve been poking around with the idea of taking planets from the solar system and altering them to look terraformed, ie, earthlike. The most logical ones to use for this purpose are Venus and Mars, since they are both terrestrial worlds near the habitable zone. Personally I’ve just been working with Mars but I may try to do one for Venus in the future.
Here’s how it works. To start with, you’ll obviously need a surface texture for your planet. Using this with any of the aforementioned GIMP-planet tutorials should give you a nice looking rendition. Here’s what I got for Mars by using a 4096x2048 texture:
Now for terraforming. In the case of Mars, this means making a thicker, bluish atmosphere, adding clouds, a biosphere, and possibly most important of all, OCEANS! \o/
For realistic oceans, you need to decide how deep they will be (how much of the land will be covered?) and then figure out what parts of the surface are below that threshold. For that, you need a heightmap. Do a google image search for ‘mars elevation map’ -- the first result is a good one and I’ll refer to that in this example.
In GIMP, place this over your surface texture. You may need to resize it and use offset to get them to match each other correctly. Now you need to make a selection on the heightmap that contains a given range of altitudes. To do this, use colors > map > ‘rotate colors’. What you’re doing is taking a select range of colors (altitudes) and changing them to a single new color. In this case the only unused color you can change them to is somewhere between violet and magenta, so on the ‘to’ colorwheel, make a tiny sliver in that area. I suggest going from 1.6 to 1.61 rad/pi. Now go to the ‘from’ colorwheel. The lower limit of the selection should be below the bluest color on the map, I’d use 1.5 rad/pi. Now swing the upper limit around clockwise from there and watch the preview, you’ll see a progressively greater area change into a purple color. This area is what will become the ocean. I used something around 0.6.
When you have a good color range, go ahead and hit ‘ok’. Now you’ll select the big purple region with the ‘select by color’ tool. You will likely need to play with the settings for feather edges and threshold, and press shift while clicking in several areas to get the whole region selected properly. Once you’ve got all the purple selected, bucket fill the whole selection with a blue ocean color. You might need to bucket fill a few times to get the edges right.
Make sure this layer has an alpha channel (right click in layer tab, ‘add alpha channel’), and then invert the selection and clear. Now it’s just your oceans sitting on top of your surface texture.
Now add the biosphere. For this, get some good looking image textures and lay them over your surface. A lot of experimentation is key, some textures will work well, some will not, and be sure to use different blending modes and play with the colors/contrast etc. You may also want to use different looking textures with certain regions of the planet or at certain altitudes. For Mars, it’d be more realistic to only have plantlife up to a certain altitude, as the air will be very thin higher up.
Once satisfied with your surface go ahead and map to sphere, add the atmospheric effects, clouds, and anything else you like.
My result for terraformed Mars:
*Images are 1024^ with alpha, can be converted to tga and used in freespace*
