Skin > Bind Skin > Smooth Bind

This menu item lets you bind geometry to any transform node or hierarchy of nodes such as an empty group node or a locator. For example, you can create a deformation effect by binding a polygonal mesh to locator nodes that are connected to the CVs of a spline curve.

Using the Smooth Bind Options, you can limit the number of joints that influence nearby skin points and limit the range of influence for joints.

See also Bind smooth skin.

Skin > Bind Skin > Smooth Bind >

Opens the Smooth Bind Options, letting you set the following options.

Bind To: Specifies whether to bind to an entire skeleton or only to selected joints. Select from the following options:

Joint Hierarchy: Specifies that the selected deformable objects will be bound to the entire skeleton, from the root joint on down through the skeleton’s hierarchy, even if you have selected some joint other than the root joint. Binding the entire joint hierarchy is the usual way to bind a character’s skin.

This is the default.
Selected Joints: Specifies that the selected deformable objects will be bound to only the selected joints, not the entire skeleton.
Object Hierarchy: Specifies that the selected deformable geometry is bound to the entire hierarchy of the selected joint or non-joint transform node, from the top node down through the entire node hierarchy. If there are any joints in the node hierarchy, they are also included in the bind. With this option, you can bind entire pieces of geometry to nodes like groups or locators.

Note
When using the Object Hierarchy option, you can only select joints or objects that cannot be skinned (for example, group nodes or locators—not pieces of geometry) as the initial influences in the bind.

Bind Method: Specifies how joints influence nearby skin points during initial skinning. See also Bind methods for smooth skinning. Select from the following options:

Closest In Hierarchy: Specifies that joint influence is based on the skeleton’s hierarchy. This is the default.

In character setup, this method can prevent inappropriate joint influences. For example, this method can prevent a right thigh joint from influencing nearby skin points on the left thigh.
Closest Distance: Specifies that joint influence is based only on proximity to the skin points. When binding skin, Maya ignores the hierarchy of the skeleton.

In character setup, this method can cause inappropriate joint influences, such as a right thigh joint influencing nearby skin points on the left thigh.
Heat Map: Uses a heat diffusion technique to distribute influence weights. Initial weights are set based on each influence object inside the mesh acting as a heat source, emitting weight values onto the surrounding mesh. Higher (hotter) weight values occur closest to the joint, and dissipate to lower (cooler) values as you move away from the object.

The following image compares the default weights assigned for a character's left arm joint using the three different bind methods.

Skinning Method: Specify which skinning method you want to use for the selected deformable object. See also Smooth skinning methods for more information.

Classic Linear: Sets the object to use classic linear skinning. Use this mode if you want basic smooth skin deformation effects, the same as in previous versions of Maya. This mode allows some volume shrinking and collapse deformation effects to occur.

When a mesh is set to linear skinning, it can lose volume in areas where it is influenced by a joint that is twisting on its axis.
Dual Quaternion: Sets the object to use dual quaternion skinning. Use this method if you’re concerned with preserving volume in the mesh as it deforms around joints that twist.

When a mesh is set to use dual quaternion skinning, volume is preserved even as it is influenced by a joint twisting on its axis.
Weight Blended: Sets the object to use a blend of classic linear and dual quaternion skinning, based on a per-vertex weight map that you paint. See Blend smooth skinning methods.

Normalize Weights mode: This drop-down list lets you set how you want smooth skin weights normalized. These options can help you avoid letting the normalization process unintentionally set small weight values across many vertices.

Select from the following options:

None: Turns off smooth skin weight normalization.

Warning
Be aware that this option lets you create weights of greater than one or less than one, which can allow for odd or incorrect deformation as you exercise the character.
Interactive: When on, Maya normalizes skin weight values as you add or remove influences, and as you paint skin weights. As you work, Maya adds or removes weights from other influences in order to make the total weights on all influences add up to 1.0. You can view the exact weights used for deformation on the skinCluster node weightList attribute.

For example, if you change a weight from 1.0 to 0.5, Maya distributes the remaining 0.5 amongst neighboring influences. This mode replicates the normalization process in previous versions of Maya.
Post: (Default) When on, Maya calculates normalized skin weight values as you deform the mesh, preventing any odd or incorrect deformation. No normalized weight values are stored on the mesh, which lets you continue painting weights or adjusting interactive bind manipulators without having the normalization process change your previous skin weighting work.

Selecting this mode lets you paint or change weights without affecting the weights for other influences, and still have the skin normalization occur when you deform the mesh.

Note
Since Maya calculates the normalized weight values dynamically at deformation time, you cannot view the normalized values on the skinCluster node weightList attribute. Your mesh will deform with normalized values, but the actual weight values on your skinCluster node may add up to more or less than 1.

If you use interactive skin binding, this mode is automatically selected for you. (See Interactive bind for smooth skinning.) As a result, for interactive binding, weights are not normalized until you deform the mesh.

For more information on skin weight normalization, see Smooth skin weight normalization and Set normalization mode and normalize weights.

Allow Multiple Bind Poses: Lets you set whether you want to allow multiple bind poses per skeleton. This option can be useful if you are binding multiple pieces of geometry to the same skeleton.

When on, you can bind the separate pieces using different bind poses for each. When off, you must bind all pieces of geometry with the skeleton in the same bind pose.
Max Influences: Specifies the number of joints that can influence each skin point on your smooth skin geometry. Default is 5, which produces good smooth skinning results for most characters. You can also limit the range of joint influence by specifying a Dropoff Rate.
Maintain Max Influences: When on, your smooth skinned geometry cannot have, at any time, a number of influences greater than that specified by Max Influences.

For example, if Max Influences is set to 3, and you paint or set weights for a fourth joint, one of the weights of the other three joints is set to 0 to maintain the total number of weighted influences specified by Max Influences.

This limits the redistribution of weights to a specific number of influences, and ensures that the primary joints are the ones that receive the weights.

Note
If you turn on Maintain Max Influences in the Attribute Editor, the skin weights are not modified until you reassign them by clicking Update Weights.
Dropoff Rate: The influence each joint has on a particular point varies with the distance between the skin point and the joint.

This option lets you specify how rapidly the influence of each joint on skin points decreases with the distance from the joint (and the joint’s bone). The greater the Dropoff Rate, the more rapid the decrease in influence. The lower the Dropoff Rate, the further the influence of each joint. Use the slider to specify values between 0.1 and 10. You can enter values up to 100, but values between 0.1 and 10 are ideal for most situations. The default is 4, which provides good deformation effects for most characters.

NoteIf the joint has a bone, the influence of the joint extends along the entire bone, from the center of the joint to the end of the bone. The joint’s influence can extend to all the points near the entire length of the bone. If the joint is an end joint (has no bone), then the joint’s influence just extends forward from the center of the joint.

After binding skin, you can use the Paint Skin Weights Tool to edit the influence of joints in an intuitive manner. For more information, see Painting smooth skin point weights.
Remove Unused Influences: When on, weighted influences that would receive a zero weighting are not included in the bind. This option is useful when you want to reduce the number of calculations for your scene to increase playback speed.

NoteThe Optimize Scene Size Options also let you remove any zero weighted influences from your character’s skin bind. You can turn on Unused Skin Influences in the Remove Unused section. For more information on the Optimize Scene Size Options, see File > Optimize Scene Size.
Colorize Skeleton: When on, bound skeletons and their skin vertices are colorized so that vertices appear the same color as the joints and bones that influence them.

Note
You can change the colors of individual joints and bones from the Display > Wireframe Color window.
Heatmap falloff: Controls the dropoff of weights around the selected joints when you select the Heatmap method of smooth skinning. This can help to reduce the amount of small weights spread across the mesh during heat map binding.

By default, Heatmap falloff is set to 0, which produces smooth results but can let small weights spread far across the mesh surface. A value closer to 1 produces a sharper falloff, which keeps weights closer to the influence object, limiting the spread of small weights.