Wednesday, June 13, 2012

How to model a sphere

To start simple, I'll try to explain how simple things can be done.Model a sphere. It seems very simple, but there are many ways to do it. Specially if you care about triangle count, ease of future modeling, UVs, symmetry, etc.

The geosphere

Here is the default sphere created by Maya. It is well shaped, but we see two annoying things
- The triangle count is quite high : 760 triangles
- There is a huge difference between faces in the pole areas and the equatorial ones.
- The default mapping is quite strange, that makes textures very deformed especially in pole regions
- The sphere is not symmetric on all planes, so it won't look the same depending on the angle of view.

First of all, reduce the polycount.
You need to modulate the number of subdivisions in the height or the radius. Theoretically, to have square faces, we should have twice more divisions around radius than height. But on low values, this gives wreid angles when the sphere is seen from the size.
That's why a 3/2 factor is often a good choice. This makes your sphere profile look similar from the side of trom the top.
For instance, you can choose 15/10 or 12/8 values.

 The SoccerBall

This is the second option. It helps to have faces of a similar size. The basic soccer ball is 116 triangles, and there are 2 size of faces, the big and the medium ones. The drawback are
- The figure is not symmetric at all. No edge loop. No nice extrusions.
- No way to cut in half
- Default UV mapping is horrible, even if mapping by face is possible.
- If you triangulate it you get an horrible topology, and see that triangle size is not so even.

You can still use a smoothed version of it, if you don't need to edit the sphere (if you're a specialized sphere-only modeler for example : )


Smoothed box modeling

The third way is to use box modeling techniques. To do this, just create a box and smooth it. You've got a sphere for 48 triangles. It's not really detailed, but the shape is correct. Could be okay for an eyeball of some enemy.

The second version is a level 2 smooth (or double smooth). this time, it's really shaped like a sphere. It has multiple advantages
- 192 triangles, for a result much better than previous 168 tris' geosphere.
- Faces are approximately the same size
- The mapping if the one of a cube, that can be quite helpfull (this can be a problem, in this case make a spherical/cylindrical uv mapping)
- The sphere is symmetric on all planes. It will look the same from top as from any side.
- It is a good object to keep modeling. You can extrude easily from any side to make a tube for example.
- The only problem could be that all the points are not on a sphere (equal distance from center), even if the volume of the primitive is the same as a sphere.

If you have any comment or your own techniques, feel free to share it.


  1. Go a step further and colapse/merge edges as you get closer to the pole.

    1. Yes, this is a good idea if you use the the geosphere model (for example if you revolve a profile). In fact the idea is to keep faces area even.
      This doesn't apply to the smoothed box because there are no poles.
      If you don't mind I'll include your pic in the article, it looks nice!