Houdini 21.0 Nodes Geometry nodes

Muscle Transfer geometry node

Transfers muscle and bones geometry between characters.

Given skin surfaces with matching topology, transfers input muscle or bone geometry between source and target characters. A mapping of the interior is computed on a tetrahedral volume mesh. This is computed automatically.

You can use Topo Transfer SOP to transfer topology between characters, as a starting point for the muscle transfer.

The surfaces are transferred point to point, so placement of topology on each character is key. Additional tools are available to help with this.

A good first step is usually Edge Relax SOP, used either on the source or target character. Set Target Mode to Scale-Independent Edge Length Distribution and enable Only Shorten Edges as well as Slide on Surface. This should result in a smoother transfer with minimized distortion.

One or both of the characters may have volumes that don’t contain any muscle, like a big belly for example. You can use Deflate SOP to flatten these areas beforehand. Additionally, if you add the resulting positions to the target mesh as targetP while leaving P unmodified, the visualizations on this node will still show the final skin mesh while using targetP as the reference position for transferring.

To make specific adjustments to where muscle outlines end up after the transfer, you can use the Topo Slide by Curve References SOP.

For more information on the workflow, see Transfer muscles to your character.

Parameters

Group

The points or primitives to transfer.

Group Type

Specify whether the Group above is a point or a primitive group.

Reference Attribute

The position attribute to use for the transfer. When this point attribute exists, it is used for the transfer instead of P. This allows you to supply a transfer target that is distinct from the skin mesh. For example, you may input a character with a big belly where the reference attribute (targetP by default) stores a deflated belly to specify where abdominal muscles go. Visualizations on this node (like the “Blend Transfer” mode) will then show the original skin mesh with the muscles transferred to the Reference Attribute position. This makes it easy to inspect the transfer result relative to the correct skin mesh.

Remesh

Remesh

Remesh the input meshes. This is done on one of the meshes and then transferred over to the other, see Remesh Reference.

Remesh Reference

Select which skin to remesh first. The remesh will then be transferred to the other skin.

Source Skin

Remesh the source skin and transfer the remesh to the destination skin.

Destination Skin

Remesh the destination skin and transfer the remesh to the source skin.

Iterations

The number of remesh iterations. Higher iterations result in higher quality. Typically no more than 3 or 4 iterations are needed.

Thin Density

The relative density of thin parts of the mesh.

Remeshing is done with the minimum resolution that still maintains the overall shape of the mesh. A low resolution is usually desirable as this results in a smoother transfer.

Thick Density

The relative density of thick parts of the mesh.

Remeshing is done with the minimum resolution that still maintains the overall shape of the mesh. A low resolution is usually desirable as this results in a smoother transfer.

Minimum Size

The minimum length of triangles produced by remeshing.

Increase Mesh Size of Empty Areas

Increase the mesh size for areas of the skin that are far away from the geometry to transfer.

Preprocess as VDB

Preprocess as VDB

Convert the mesh to a VDB and back to mesh before remeshing. This can solve a lot of problems with self intersections as well as remove excessive detail.

Voxel Resolution

The resolution of the VDB along the longest axis.

Smooth Iterations

Smooth iterations to perform on the VDB. Some smoothing is usually desirable as it helps prevent small surface details influencing the transfer.

Transfer

Use Interior Geometry

Use interior geometry connected to the 2nd and 3rd inputs to control the transfer. When enabled, additional tetrahedra may be created around interior geometry. During the transfer, the points of tetrahedra close to interior geometry are constrained to the interior geometry.

Interior Group

A subset of the interior geometry to use in the transfer.

Rigid Transform

Transfer geometry using a best fit transform instead of deforming.

Rigid Group

A group of geometries to transform rigidly. This may be useful for transferring bones.

Use Mask Attribute

A mask attribute specifying how rigidly each point in the first input should be transferred. See Rigid Transform.

Mask Attribute

The name of the rigid mask attribute. See Rigid Transform.

Blur Iterations

Number of blur iterations to perform after the transfer. This can be used to smooth the result of the transfer.

Deform Mode

Specifies how input geometry is deformed using the computed tetrahedral volume mesh.

Point Capture & Deform (Fast)

Uses Point Deform SOP internally to deform input geometry by the computed tetrahedral mesh.

Solid Volume Capture & Deform (Smooth)

Performs a higher quality (but slower) deformation, usually a good mix of smooth transfer and detail preservation.

Minimum Points

Minimum number of points to use with Deform Mode:Point Capture & Deform (Fast).

Guides

Visualization

The geometry to display when in the viewer state.

Source Skin

Show the source skin. This can be used to tweak remesh settings with fast feedback.

Destination Skin

Show the destination skin. This can be used to tweak remesh settings with fast feedback.

Both Skins Side by Side

Show the source and destination skin. This can be used to tweak remesh settings with fast feedback.

Blend Skins

Blends between both remeshed skins. This can be used to check how points shift during the transfer.

Blend Transfer

Blend the final result of the transfer, with the skin drawn transparently.

Match Source Mesh Size to Destination

Match the sizes of each input for easier comparison when characters have vastly different sizes.

Blend

Blend visualizations between source and destination character.

See also

Geometry nodes