Texturing an asteroid

Question

I'm trying to texture this asteroid so it looks reasonable. I'm missing something though.

Following this tutorial, I got this so far.

Now I don't understand the next step: how do you resolve the seam problems? This icosahedral sphere has a seam running through it that cannot be avoided. Ok. How do I paint the texture so it looks seamless when applied to the object? How do I know which edge connects to what side? I guess it will just be symmetrical?

This seems awfully hard to texture a simple sphere. Am I missing some technique here?

Answer 1

This is where I will use a 3D painting program. I primarily use Blender for my modeling, and it has a 3D painter built in. Being able to paint directly on the model in a 3D environment, makes the strokes continue across seams.

I don't find the paint tools in Blender to be great, so I'll usually switch to something like GIMP once I've got a rough idea. Then I add details in GIMP. Though, your 3D paint program may be different.

The program you use will depend on your work flow, but here's a tutorial (and another) for using Blender's 3D painting capability.

Answer 2

One simple solution is to keep the background of the asteroid very flat so it wraps well, then add detail away from the edges. Don't cross the edge. Put your craters and bumps and things inside. That should minimize the seam.

Answer 3

I was able to get a reasonable wrap using this kind of UV layout:

It's only got 2 seams, one in the top, and one in the bottom (edges 1 and 7 from the diagram above).

The texture is tileable, so along the rest of the seam, it is seamless.

I couldn't figure out another way to do it!

Answer 4

I also thought just now about using a cubemap texture (ie 6 textures). My rationale is, if you were planning to use a 256x256=65536 texel image, you may as well use a 64x64x6=24576 texel image (cheaper!) and get less distortion and no poles.

You lay the UV mapping out like this:

Identifying what side is what and laying out the UV's this way is tedious but not very hard.

You have to create a cubemap texture to put on the sphere. I didn't have a rocky one, so I just used one from http://humus.name/. It's important to note tileability isn't enough for a cubemap: you have to have continuity across the edges of the cubemap (just fold a paper cube to figure these out!)

Answer 5

You could texture map it by pretending it's a sphere or a cube. The quality of this approximation depends on how round your asteroids are.

With sphere treat each vertex position as a normal and convert them to polar coordinates. This will create poles though, but at least it will be seamless.

With cube you can create 6 faces that are seamless. Alternatively you can just use a cube map by again treating all vertex positions as normals and sampling from a cube map with that.