A simple NURBS patch with a bulge, created by skinning two joints.

Attempting to remove the bulge quickly by re-skinning to the joint that created it gives you poor results. Further modification of the skin is necessary to get it closer to the desired default flat surface you started with.

So why the neutral pose? What makes it easier to deform than an action pose? The answer can be summed up in one sentence: It is easier to add a bend, crease or bulge in a model than take one away.

Much of this has to do with the falloff associated with the points, the distance to the deforming node, and relative position of the points to other points. It’s something you’ll get the feel for and it’s difficult to explain, but it’s easy to demonstrate.

For this demonstration, you want to create a bulge in a flat surface.

1. Create a flat NURBS plane with 16 divisions in each direction.
2. Make a few joints to bind to the surface. Make one long joint below the surface and one single joint at the origin to translate up and down.
3. Use the Paint Weights tool to confine your bulge to a small part of the center of the patch. (For more information on the Paint Weights Tool, read the Maya Documentation.)
4. Transform your joint in Y to make a bulge in the NURBS plane. By transforming the joint, you can make either a bulge, a depression, or you can return to the original shape of the surface.

Now let’s try to remove a bulge that we have on this surface, to return our surface to its original shape.

1. Translate your joint to create the bulge again.
2. Select the plane and delete the history on the NURBS surface.
3. Now rebind your joint to the surface. Paint weights on the CVs as you did in the previous example.
4. Translate the joint back to the origin and remove the bulge when you place the joint back at the origin.

Notice that it isn’t easy to blend the bulge out. In this case, you’ll probably need to go in and adjust the values point by point to achieve a flat surface. Another factor is that the further you push the joint from the bind pose, the more problems you will see in the deformation of the skin. Try this type of experiment in other situations; for example, create an elbow crease with a deformation, and then try to take a sculpted crease out with another type of deformation. This kind of work makes the bulge exercise look like a walk in the park. Above all else, this lesson should motivate you to make good decisions about your geometry, whether you’re building it yourself or working on it with others.