Houdini 11 Nodes Surface nodes

Measures volume, area, and perimeter of polygons and puts the results in attributes.

The volume of a polygon is the volume of the pyramid defined with the polygon as the base and the specified point as the apex. This volume is signed and can be summed with those of other polygons to get the actual volume of a 3D object. This summation can be done with an Attribute Promote SOP.

The area of polygons is only exact when they are planar. Otherwise it is the area of the triangle fan of the polygon from its barycentre.

It can also be used to compute an approximation of the curvature at the points of the input geometry. The curvature is a measure of the difference between the point normal and the spread of all the edges a point shares. A point shared between planar surfaces will have a curvature of 0.

Note

Bezier and NURBs curves use the measurements of the polygon which shares their control points. Bezier and NURBs patches use the measurements of the mesh which shares their control points.

Tip

To birth particles based on primitives' areas, use one of the following emission types in your source pop: Edges (attribute), Prim Center (attribute), and Surfaces (attribute). These use the 'Distribution Attribute' from each primitive as the probability distribution. See the Source POP for more info.

## Parameters

 Group The group to be measured. This will be a primitive group for Area or Perimeter measurements and a point group for Curvature measurements. Type The type of measurement to be performed. It is one of Area, Perimeter, Curvature, or Volume. Override Name Determines if the default attribute name should be used. The default name is `perimeter` for perimeter, `area` for area and `curvature` for curvature. Attribute The name of the attribute to store the generated measurement in, if the default is not used. Min/Max The curvature computed will be clamped between the two values specified. Center The point used as the apex of the pyramid when calculating the volume of a polygon. The pyramid is defined with the polygon as its base and this point as its apex.