Polygon Reduction Op Property Editor

| General | Feature Preservation | LOD Controls

Reduces the number of polygons by collapsing edges.

To apply: Select one or more polygon mesh objects, polygon clusters, or polygons and choose Modify Poly. Mesh Polygon Reduction from the Model toolbar.

To redisplay: Select the reduced object, click the Selection button on the Select panel, then click the Polygon Reduction Op icon.

General

Reduction Amount

Unit	Controls how the amount of reduction is specified: Ratio allows you to set the amount of reduction as a percentage using the Ratio slider. Final vertex count lets you set the number of vertices in the result using the Vtx Count slider. Final triangle count lets you set the number of triangles (polygons after tessellation) in the result using the Tri Count slider.
Ratio	Sets the amount of reduction as a percentage of the original number of polygons. This slider is available only when Unit is set to Ratio. Note that the operator may not be able to achieve the exact amount of reduction because of other settings.
Vtx Count	Specifies the final number of vertices. This slider is available only when Unit is set to Final vertex count. Note that the operator may not be able to achieve the exact amount of reduction because of other settings.
Tri Count	Specifies the final number of triangles (polygons after tessellation). This slider is available only when Unit is set to Final triangle count. Note that the operator may not be able to achieve the exact amount of reduction because of other settings.
Smooth transitions	Shrinks edges before they collapse as the reduction amount is increased. In addition, corresponding properties, such as texture UVs and vertex colors, are interpolated. This allows the object to gradually morph when the reduction amount is animated, and avoids sudden popping in the object's shape or textures as edges collapse. It is particularly useful when combined with Reduce parallel edge loops or LODs. This option is also available on the LOD Controls tab.

Connected Weight Map

Allows you to use a weight map to control the amount of reduction in different areas. Connect or disconnect a weight map by right-clicking on the connection icon to the right of the Multiplier slider.

The cluster that contains the weight map must exist before you apply the Polygon Reduction operator. If you want to add or remove points from the cluster or paint weight strokes later, make sure you disable the Polygon Reduction operator first.

If Invert is on, areas in which the weight map has a low opacity are more likely to be reduced than areas with a high opacity. Areas with a weight of 1 are reduced last; they are essentially protected from reduction unless the reduction amount is so high that the other areas of the weight map cannot be reduced further.

Multiplier	Modulates how strongly the values in the weight map affect the likelihood of edges collapsing.
Invert	Reverses the effect of the weight map. When this option is off, areas of low opacity are protected and areas of high opacity are reduced.

Shape

Sharpness

Controls the balance between preserving small, sharp details versus larger shapes. At low values, details that are small relative to the general shape of the object are more likely to be collapsed. At high values, they are more likely to be kept.

Preserve volume

Rearranges vertices to keep the object's volume unchanged. When an edge is collapsed into a point, the difference in the dihedral volume is calculated and the point is moved along its normal to compensate. In some cases, this can help maintain an object's silhouette and prevent protuberances like fingers and limbs from disappearing. However, it can also distort an object's shape especially at high reduction amounts, so use the slider to achieve a good balance.

Quad Preservation

Reduce Parallel Edge Loops

Collapses an entire set of parallel edge loops together, instead of collapsing individual edges one at a time.

Although this option is incompatible with Enforce symmetry, it tends to preserve symmetry on truly symmetric objects anyway.

Preserve quad lines

Provides relative control over the amount of quads remaining in the result. After the edge with the lowest energy is collapsed, edges that were parallel to it become temporarily more likely to be collapsed next (as if their energy has been lowered). Use the slider to control the strength of the effect: the higher the value, the more quads in the final result. A value of 0 is equivalent to turning this option off.

Symmetry

Enforce symmetry

Preserves symmetry during reduction. If you don't use a symmetry map, the reduction operator uses its own internal method for determining which edges are symmetric. This allows it to find local symmetries, such as between the two sides of the same finger, in addition to global symmetries such as between the fingers of opposite hands.

However, if an object has multiple planes of symmetry (like a sphere), the internal method will arbitrarily pick one pair out of many possible symmetric edges. In such cases, it may be preferable to use a symmetry map.

Use symmetry map

Uses the connected symmetry map to determine which edges are symmetric. Right-click the connection icon to connect or disconnect maps. When a map is connected, symmetry is always enforced; you do not need to explicitly turn Enforce symmetry on.

A symmetry map is useful when the object is not in its base symmetric shape. It also resolves ambiguities when there are multiple planes of symmetry, and ensures that symmetrical edges are always found in spite of possible numerical imprecisions in calculations. The symmetry map must already exist before you apply polygon reduction.

Tolerance level

The maximum difference in energy between symmetric edges. If a symmetric edge has an energy difference greater than the tolerance, it is not collapsed automatically (although it may still be collapsed later in the process, depending on its own energy).

When a symmetry map is connected, this value is ignored.

Feature Preservation

Preserve

Controls the priority given to preserving edges that meet the corresponding criteria. Setting a slider to its maximum value preserves the corresponding edges completely, and may prevent the operator from reaching the amount of reduction set on the General tab. Setting a value of 0 means that the criterion is not considered at all when reducing polygons. Turning a checkbox off is equivalent to setting a value of 0.

Boundaries	Edges that are shared by only one polygon.
Input cluster boundaries	Boundaries of the polygons or polygon clusters on which you applied reduction (if you did not apply it on an entire object).
Connected vertex cluster	Edges adjacent to vertices in the connected cluster. Use the connection icon to connect or disconnect a point cluster. The cluster must exist before you apply polygon reduction.
Hard edges	Edges that have been marked as hard using Modify Component Mark Hard Edge/Vertex.
Creases	Edges that have had crease values set using Modify Component Set Edge/Vertex Crease Value.
Material boundaries	Boundaries of polygon clusters with local materials.
Property discontinuities	Breaks in the texture UVs, user normals, or vertex color (CAV) properties. User data is not considered.

Optimize for attributes

Biases the reduction process by taking into account value differences in other properties. A value of 0 ignores the attribute when considering an edge for reduction, while non-zero values set a weighted priority which is considered together with the edge's geometric energy.

UV weight	The priority given to differences in texture UVs when choosing edges for collapsing.
Color weight	The priority given to differences in vertex colors (CAVs) when choosing edges for collapsing.
Weight map weight	The priority given to differences in weight map values when choosing edges for collapsing.
User normals weight	The priority given to differences in user-defined normals when choosing edges for collapsing.
Use existing vertex position	Normally when an edge is collapsed, the new vertex is created at the midpoint of the edge. However, if this option is active, then edges collapse to one of the two endpoints. This means that each point in the reduced object shares its position with a point in the unreduced object. This could be useful in some situations, for example, if you are exporting several version of the geometry for use with an engine that does not interpolate attributes. If you are using this option, you probably also want to set Preserve volume to 0 on the General tab; otherwise, points will be moved after edges are collapsed and the positions will no longer correspond. You should also be aware that Use existing vertex positions may break symmetry if edges cross the plane of symmetry.

LOD Controls

Use LODs

Allows you to generate several versions of an object at different levels of detail. The operator precalculates the geometry for each version and caches the results.

Control by LOD Stage

Activate

Controls how the active LOD is specified.

If this option is off, adjust the Reduction Amount on the General tab of the Polygon Reduction Op node. The LOD which is closest to the amount of reduction is used. If Smooth transitions is on, reduction amounts that fall between discrete LODs morph between the levels.
If this option is on, specify the LOD directly using LOD Stage. This is especially useful if you want to export LODs for game content or other purposes.

LOD Stage

Specifies the current LOD (when Activate is on): The meaning of the stages depends on whether Smooth transitions is on or off.

If Smooth transitions is off:

0 is no reduction.
1 is the first level of reduction.
2 is the second level of reduction, and so on.

If Smooth transitions is on:

0 is no reduction.
1 is the unreduced object morphed to first level of reduction. Edges have been shrunk to zero length but coincident points have not been merged. It has the same number of vertices as level 0.
2 is the first level of reduction, after coincident points have been merged.
3 is the first level of reduction morphed to the second level of reduction, and so on.

Settings

Reduction Ratio per LOD	The percentage of reduction applied successively at each LOD. For example, if this value is 50, the first LOD has a reduction of 50%, the second LOD has a total reduction of 75% (half of the remaining polygons), the third LOD has a total reduction of 87.5%, and so on.
Max ratio	Sets the maximum total amount of reduction. This overrides the amount of reduction set on the General tab, and prevents the object from becoming too distorted at high reduction amounts.

Transition

Smooth transitions

Shrinks edges before they collapse as the reduction amount is increased. In addition, corresponding properties, such as texture UVs and vertex colors, are interpolated. This allows the object to gradually morph when the reduction amount is animated, and avoids sudden popping in the object's shape or textures as edges collapse. It is particularly useful when combined with Reduce parallel edge loops or LODs.

This option is also available on the General tab.

Transition size

Restrict the interval during which the morphing occurs to a fraction of the interval between LODs.

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