You can filter polygon mesh objects to clean up areas by removing components that match certain criteria, for example, small components that represent insignificant detail. You can filter edges, points, and polygons.
Edge filtering removes edges by collapsing them based on either their length or angle. In both cases, you can protect boundary edges with the Keep Borders Edges Intact option.
Edge filtering is especially useful for reducing the triangulation on polygon meshes generated by Boolean operations.
When you filter edges by length, the shortest edges are collapsed.
When you filter edges by angle, points are collapsed if they are shared by exactly two edges whose angular difference is less than a threshold you specify.
This lets you combine edges that are almost colinear. Points that are shared by three or more edges are never collapsed.
Filtering points on polygon mesh objects welds together vertices that are within a specified distance from each other. Among other things, this can be very useful for fixing disconnected polygons in " exploded" meshes which can occur when meshes are exported from some other programs.
Select the points or point clusters that you want to filter on a polygon mesh object. Selecting an object is equivalent to selecting all its points.
Choose Modify 
Poly. Mesh Filter Points from the Model toolbar.
The selected points are filtered with the default settings and the FilterPointsByDistance Op property editor opens.
Adjust the Distance. Points that are closer to each other than this value are welded together. Points that are farther apart than this value may get welded into separate "clumps". Values are in Softimage units.
If desired, specify the targets for welding:
Average position welds each clump of points in the selection together at their average position.
Selected point welds each clump of points in the selection together at the position of the point that is nearest to the average position.
Unselected point welds each selected point to an unselected point on the same object.
If desired, adjust the other parameters as described in the sections that follow.
There are two options in the Cleanup box of the FilterPointsByDistance Op property editor that remove undesirable geometry that may result from filtering points:
Remove new double-sided polygons eliminates pairs of back-to-back polygons created by the filtering process. These double-sided polygons can occur where two polygons face each other across a narrow gap. In most situations, you probably don't want such double-sided polygons in the final result, so it's best to leave this option on. However, you can turn it off if you intend to use the resulting polygons for further modeling.
Collapse new double edges removes double edges created by the filtering process. You can turn this option off, for example, if you want to weld two rows of non-boundary points without collapsing them all to a single vertex.
A couple of options in the FilterPointsByDistance Op property editor allow you to restrict the filtering process to vertices that meet specific criteria:
Border points only welds only points on boundary edges, even if non-border points were included in the selection. This option is useful, for example, when joining pieces that were modeled separately and then merged into a single object.
Max normal angle difference welds two points only if the difference between their normal angles is less than the specified amount. This option can be used to prevent points that are facing in opposite directions, such as on the front and back of a character's arms, from being welded together. Activate the checkbox and then adjust the slider. Values are in degrees.
Connected user target cluster lets you specify a cluster of points that act as "preferred targets" and are never collapsed to other points. Click the connection icon, then choose Connect and pick a cluster. If you change your mind, click the connection icon again and choose Disconnect.
When filtering polygons, you can remove them based on their area or their dihedral angles. In both cases, you have the option of cleaning up edges afterwards.
As an alternative to filtering polygons, you can apply polygon reduction. For more information, see Polygon Reduction.
When you filter polygons by angle, adjacent polygons are merged together if their dihedral angle is less than the threshold you specify. Small angles correspond to flat areas, so this method preserves sharp detail.
Choose Modify Poly. Mesh Filter Polygons. The Polygon Filter Op property editor opens.
Polygon Incidence Angle is the threshold for merging polygons. Adjacent polygons whose dihedral angle is less than or equal to this value are combined.
Dissolve by Pair combines polygons sequentially, one pair at a time. This ensures that, for a given polygon, the adjacent polygon being considered for co-removal is the most nearly coplanar one.
If this option is off, polygons are dissolved all at once and the end result may consist of large, non-planar polygons.
When you filter polygons by area, the smallest polygons are removed. This eliminates small, "noisy" details.
Choose Modify Poly. Mesh Filter Polygons. The Polygon Filter Op property editor opens.
Polygon Area is the threshold for removing polygons. Polygons with an area smaller than this value are removed.
Action is the method used to remove polygons: Dissolve or Collapse. For a description of the different methods of removal, see Removing Polygon Mesh Components.
In particular, note that Dissolve will remove areas of adjacent small polygons, but not a single small polygon surrounded by larger ones.
When you filter polygons, you have the option of filtering the edges afterwards. Filter Sub Edges in the Polygon Filter Op property editor cleans up edges that are no longer necessary after removing polygons. If a vertex is shared by three or more polygons before filtering, but only by two polygons after filtering, then it is collapsed.
Filter Sub Edges does not affect points that were already shared by only two polygons before filtering, and in particular, it will not affect boundaries.
To remove those points, filter the edges as described in Filtering Edges.
Here are some tips related to filtering polygon mesh components:
Although you can filter an entire object, it's usually better to select specific areas of components. Often, there are large areas of your object that you do not need or want to be filtered, and by leaving these areas out, you can speed up the operation significantly.
In addition, selecting components for filtering gives you more control because you can use different criteria in different areas.
The component filter property editors show statistics on the total number of components on the object. This information can be useful if you need to meet certain geometry requirements for games or other specific applications.
