Specifies the trim curves that the processor will use. You can select parameter space curves ( ), model space curves ( , or use the flag that is present in the .IGES file ( ). is the default. If the value is not specified, we use 3D world space curves, and if not available, 2D parameter space trimming curves.
When ON, Alias detects trimmed surfaces whose trim boundaries are the same as, or iso-parametric to, the natural boundaries of the untrimmed surface. It then converts these surfaces into Alias surfaces by shrinking the untrimmed surface to the trim boundaries.