Poly Reduce surface node

Reduces the number of polygons in a model while attempting to preserve its shape.

See also: Dissolve,

The optional second input’s polygons represent feature edges. The optional third input’s polygons may be used as a reference. The second and third inputs are matched to the first input mesh by point numbers.

The methods to reduce polygonal models are:

  1. A percentage of their former size

  2. A specific number of polys (within a few)

  3. According to distance from a camera

  4. A specific list of edges to collapse

Note that as it uses a triangular mesh internally, the polygon counts all refer to a count in triangles.

A second input for feature edges is provided. A third input for reference is provided.

Tip

To get a uniform distribution of polygons you may need to turn up the Equalize edges parameter beyond the 0-1 range, to 10 or even 100.

Using PolyReduce

  1. Select the object whose polygons you want to reduce.

  2. Click the PolyReduce tool on the Polygon tab.

  3. Select the crease edges, if any, and press Enter when finished.

  4. Reduce the polygons by a percentage of the initial amount, number of polygons, or according to distance from a camera in the parameter editor.

Note

This tool requires a triangular mesh, which may increase the initial polygon count.

Parameters

Polygons

The polygons which will be candidates for simplification. Other polygons which share points with these might also be affected.

Features

Which polygons are feature edges.

Percentage

Choose reduction level with a percentage.

Keep %

The percent of polygons to keep. This is with respect to the triangulated mesh.

Number of Polygons

Specify a desired number of polygons.

Keep #

The desired number of triangles in the simplified model. The resulting number may be slightly less than this.

Distance

Reduce polygons based on distance to an object.

Object

The object to use as a reference.

Dist. Threshold

The world distance at which the polygons should be left at full detail.

Minimum %

A lower bound to the level of reduction.

Edge List

Collapse specific edges in an optimal fashion.

Edge List

List of edges to be candidates for collapsing.

Limit Number of Collapses

Only collapse up to this number of edges, picking the ones that affect the geometry least first.

Number of Collapses

The maximum number of edge collapses to perform from the list.

Optimization

Controls how new points are found when an edge collapses. An optimizaiton of 1 will try to place the point to minimize the change to the surface. A value of 0 will place the point in the midpoint of the edge.

Stiffen Border

Without any constraints, the edges of planar surfaces can erode. This controls a bias which penalizes such erosion.

Stiffen Features

The amount of penalty to add to the feature edges being eroded.

Equalize Edges

This bias penalizes the removal of long edges. It tends to reduce high aspect ratio triangles at the expense of more uniform reduction.

Attrib Weight

This bias uses the point attribute “weight” to control the polygon reduction. Points with a larger weight value will be more resistant to collapse and better preserve the original surface geometry.

Topological Weight

This biases against vertices which have a large or small number of connected edges. Adding a topological weight results in a more uniform triangular mesh topology which can result in better tristripping.

Prevent Mesh Inversion

When enabled, each reduction is tested to see if it would flip a triangle normal. While incurring a slight cost, the results are almost always worth it.

Pre-Triangulate

Converts the mesh to triangles before reduction. This gives more freedom in how the mesh can be reduced.

Prevent Cracking

This prohibits the removal of any edge that occurs at the boundary of the polygons. This ensures no cracks develop with unreduced areas.

Use Original Points

When it collapses edges, it will use one of the two original points instead of finding the optimal interior point.

Frame

When enabled, the specified frame is used as a reference for the polygon reduction process. The input geometry should be topologically invariant.

Use Reference Input

When enabled, the third input is used as the reference geometry on which the polygon reduction process is based. The input and reference geometries should be topologically equivalent.

The reference geometry is first processed by the polygon reduction algorithm. The results of which are then applied to the input geometry.

Animating input geometry that is fed through the PolyReduce SOP will exhibit flickering, since the PolyReduce SOP will give different results for different edge lengths. To avoid the flickering, turn on the options “Frame” and “Use Reference Input”. Using static geometry will not produce flickering. The “Frame” option specifies that a particular frame be used either from the input or the reference geometry.

Usages in other examples

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