vector primduv(string geometry, int prim_number, vector2 uv, int du, int dv)
A string specifying a geometry file (for example, a
.bgeo) to read from. When running inside Houdini, this can be an
The number of the primitive on which to measure the derivative.
The parametric coordinates on the primitive at which to measure the derivative.
Represent the derivative order to query.
On a curve, the curve direction is given by
du==1 and the curvature is given by
This only works on NURBS and Bezier curve primitives.
du is currently ignored as it is meant to work with parametric surfaces.