METHOD AND SYSTEM FOR EFFICIENTLY TRIMMING A NURBS SURFACE WITH A PROJECTED CURVE

摘要

A curve projected onto a NURBS surface defines trim regions on theNURBS surface. A plurality of spaced-apart points are defined on the curve andrays are project through the points toward a NURBS surface. Any intersections ofthe rays with the NURBS surface is mapped into the U,V domain. Correspondingpoints of adjacent rays are connected to define at least a portion of each trim regionon the NURBS surface. Transitions on the NURBS surface between adjacent raysare detected based upon differences in the number of intersections of adjacent rays.The location of each transition is determined to within a selected tolerance by usinga binary subdivision of the interval between adjacent rays. The location of suchtransitions is used to determine how intersections of the rays with the surface at theboundaries of the NURBS surface should be connected. Parity assigned to the raysat each intersection determines the direction in which intersections along the raysare connected. The technique enables real-time trimming of the NURBS surface tobe carried out in response to any change to the curve and/or NURBS surfacetopology.