Special points and curves force the triangulation of a free-form surface to include specific features. A special point is given in the parameter space of the surface and will be included as a corresponding vertex in the triangulation. A special curve is similar to a trimming curve but does not cause portions of the surface to be trimmed. Rather, the curve is included as a polyline in the triangulation of the surface. Special curves are useful for introducing flexibility in the triangulation along specific features. For example, if letters were to be embossed on a planar surface using displacement mapping, a series of contour curves around the letters could be created with special curves.
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