Downloaded from https://www.everyspec.com APPENDIX C MIL-STD-31000A The Greville algorithm should be used to sample points on all NURBS surfaces and all edge curves. In general, when two NURBS surfaces intersect, the curve that defines the intersection edge will not be coincident with the actual intersection but will approximate it within an accuracy specified by the 3D modeling system. Consequently, it is important to check that both edge curves and surfaces have not deviated from their sample points by more than the specified tolerance (described below). Figure 4. An example of Greville points on both a surface and its edge curves. 73