Houdini 21.0 Nodes Geometry nodes

Tissue Solidify Otis geometry node

Solidifies an input surface or shell into a volumetric tissue structure composed of tetrahedra, ready for simulation with Otis Solver SOP.

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Since 21.0

This node prepares anatomical geometry for soft tissue simulation by generating a tetrahedralized volume from an exterior surface mesh, optionally using interior muscle and bone geometry for structural context. The result is a layered soft-tissue representation made of two tetrahedral components: the Tissue Mesh (fat layer) and the Core (deeper soft-tissue or fascia). These are suitable for direct use in simulation pipelines driven by Otis Solver SOP.

Depending on the selected Method the node can create geometry suitable for combined muscle and tissue simulation or focus solely on the fascia suitable for holding muscles together. The solidification process follows a structured multi-stage pipeline:

Exterior Remesh

The outer surface is optionally remeshed for improved triangle quality, resolution, and gradation. This stage uses the controls under the Exterior Remesh folder to determine triangle sizes and smoothing behavior.

Inner Surface

An interior surface is generated by shrink-wrapping the exterior around nearby interior structures such as bones and muscles. This forms the boundary for the Core region and provides the surface triangles used for colliding against interior structures.

Tissue Mesh

A closed triangulated mesh is constructed between the exterior and the shrinkwrapped inner surface. This mesh defines the tissue “shell” or fat layer.

Note

In Core Only and Fascia modes, this stage is skipped because only the inner region is needed.

Tetrahedralization

The relevant meshes are converted into tetrahedral volumes. The specifics depend on the selected Method:

Core Only and Fascia Modes

Only the shrinkwrapped Inner Surface is tetrahedralized.

  • In Core Only mode, this results in a single solid core.

  • In Fascia mode, the core’s surface triangles are reversed (resulting in inward-facing normals) to support proper collisions against internal structures like muscle and bone.

Fused Tissue and Core / Separated Tissue and Core Modes

Both the Inner Surface and the space between inner and outer surfaces (the Tissue Mesh) are tetrahedralized.

  • The Inner Surface becomes the Tissue Core Layer, representing deep connective tissue.

  • The Tissue Mesh becomes the Tissue Solid Layer, representing fascia & fat.

Additionally, the triangulated surface of the Tissue Mesh is retained in the output geometry. This layer is essential for detecting and resolving collisions in simulations handled by Otis Solver SOP.

Tip

Use the Visualization parameter to preview key stages of the solidification pipeline, including remeshing, shrinkwrapping, and tetrahedral layout.

Parameters

Group

Specifies the subset of the input geometry to solidify.

Group Type

Specifies the type of elements to include from the group.

Guess from Group

Automatically infers the group type.

Breakpoints

Treats group as breakpoints.

Edges

Uses edge groups.

Points

Uses point groups.

Primitives

Uses primitive groups.

Keep Single Biggest Piece

When enabled, keeps only the largest connected component of the input geometry. Useful for cleaning up unwanted floating geometry.

Visualization

Choose which stage of the solidification process to visualize in the viewport.

Exterior Remesh

Displays the remeshed outer surface.

Inner Surface

Displays the wrapped inner core surface.

Tissue Mesh

Displays the generated triangles for the outer tissue.

Core Tetrahedra

Displays the core’s tetrahedra only.

Shell Tetrahedra

Displays outer layer’s tetrahedra only.

Method

Selects the construction approach for the tissue geometry.

Fused Tissue and Core

Creates a continuous tetrahedral structure containing both outer tissue and inner core layers fused together.

Separated Tissue and Core

Generates separate tetrahedral meshes for tissue and core.

Note

This is currently only provided for convenience. It is not supported direcly by Otis Configure Muscle and Tissue SOP as simulation geometry.

Core Only

Only generates the tetrahedral core. No outer tissue mesh is created.

Fascia

Only generates the tetrahedral core. No outer tissue mesh is created. Surface triangles are reversed with normals pointing inward.

Tip

Use this to hold muscles together and close to bone geometry when you don’t want to run a full tissue sim using Fused Tissue and Core.

Exterior Remesh

Remesh Exterior Surface

Enables remeshing of the outer surface prior to tetrahedralization. Note that in the Tissue and Core modes, triangle size is also affected by the parameters in the Tissue Volume folder, particularly those related to outer layer thickness. Remeshing is strongly recommended in those modes to ensure best tetrahedralization quality.

Iterations

Number of remeshing passes. More iterations smooth and distribute edge lengths more consistently.

Min Size

Minimum target triangle size in the remeshed output.

Max Size

Maximum target triangle size in the remeshed output.

Relative Density

Multiplier for triangle size relative to the original mesh resolution. Controls global remeshing density.

Gradation

Controls how gradually triangle sizes are allowed to vary. Lower values produce more uniform remeshing.

Visualize Exterior Remesh

Shows the remeshed surface directly in the viewport.

Inner Surface

Blur

Applies blurring to selected regions of the input skin mesh before computing the shrink-wrapped inner surface. This is especially useful for removing narrow or delicate features like ears or small tentacles that don’t have corresponding interior geometry.

Note

A blur mask attribute is required. Blurring the entire skin mesh is not recommended, as it may cause intersections with interior muscles or bones, leading to issues during shrink wrapping.

Blur Mask

Specifies the name of the mask attribute that defines which regions of the mesh should be blurred. Areas with non-zero mask values will be affected.

Blur Iterations

Sets the number of iterations used for the blur operation. Higher values result in stronger smoothing.

Tip

To fully eliminate appendages like ears, a large number of iterations (hundreds or even thousands) may be required.

Shrink Wrap Iterations

Number of iterations to shrink the core surface toward the interior of the tissue. Higher values may be needed when fitting a character that has areas of thick fat.

Slope Angle Limit

Prevents the shrink-wrap surface from creeping into gaps between muscles and bones. Lower values produce more of a tight shrinkwrap over these gaps. Fitting too closely to gaps can produce some undesirable effects when tissue slides over muscles & bones.

Smoothing

Applies smoothing to the inner surface after each shrink-wrap iteration.

Final Detangle

When enabled, performs a final detangling pass on the shrink-wrapped core surface to prevent self-intersections or overlaps.

Visualize Inner Surface

Displays the wrapped inner core surface in the viewport.

Tissue Volume

Minimum Thickness

Specifies the minimum allowed thickness for the tissue volume between outer and inner surfaces. Prevents overly thin or collapsed tetrahedra.

Shell Tet Squash Ratio

Controls the aspect ratio tolerance for tetrahedra in the shell layer. Values closer to 1 produce more uniform tetrahedra; lower values allow for flatter elements.

Visualize Tissue Mesh

Displays the generated tetrahedral tissue mesh in the viewport.

See also

Geometry nodes