All images from Maya 2008 Character Modeling and Animation by Tereza Flaxman.

This month, VFXWorld begins excerpting a new series from the Thomson Course Technology book Maya 2008 Character Modeling and Animation. VFXWorld readers will take on the challenge of animating realistic and compelling characters using the latest version of Maya, the powerful 3D graphics and modeling software. Excerpts will show beginning to intermediate animation students and enthusiasts how to create professional quality characters, explaining the full character animation process from pre-production to final full body and facial animation.

Maya has a powerful set of methods for attaching geometry to control skeletons. This excerpt from Chapter 4 shows how to set up a very simple skinned joint using a method called "smooth bind." Let's start by considering the man concepts.

Bind Skin
Binding skin is the process of attaching a deformable object such as a lattice or geometry to joints or a skeleton. When a deformable object is bound to a skeleton, Maya attaches the points of the geometry to the joint in a hierarchy. Points are NURBS control vertices (CVs), polygon vertex or lattice points.

Maya has two skin bind types: smooth and rigid. In a smooth bind, more than one joint influences each point. This causes a smooth geometry deformation when you bend the joints, as shown in Figure 1.

[Figure 1] Smooth binding.

Smooth Bind
Maya offers two smooth bind methods. You can choose to attach the points to the closest joint in the hierarchy or closest in distance. When you choose the Closest in Hierarchy option, Maya determines which joints in the hierarchy are closest to each point and assigns point weights that control the influence of the joints on each point. When you choose the Closest Distance option, Maya ignores the joints hierarchy and assigns point weights based on closeness. This method may cause undesirable geometry deformation. For example, when a hand skeleton is bound to the geometry, the vertices of the finger geometry may be influenced by the joints of two fingers, as shown in Figure 2. This occurs because the finger joints of adjacent fingers are closer to each other than they are to their parent joint.

The Closest Distance option is useful in situations where the joint hierarchy does not allow Maya to determine the next logical parent or child joint to consider in binding. In complex rigs, there can be multiple grouping nodes and control objects between separate sub-skeletons. In these cases, the Closest in Hierarchy option will fail to assign some joints and thus the Closest Distance option is more appropriate. Note that while you cannot use more than one bind method simultaneously on the same geometry, you can use different methods on different portions of a character. For example, the torso might be bound using Closest Distance and the arms using Closest in Hierarchy.