PROBLEM TO BE SOLVED: To provide an interference line generating device capable of calculating an interference line between free curved surfaces containing irrational trim curved surfaces at high speed.;SOLUTION: When a curved surface is an irrational trim curved surface, a point on a generating curve with a minimum distance to a control point on a generating curved surface of the trim curved surface is found by a minimum distance point group preserving means 11. Next, all areas included in a trim area are found by an area calculating means 12. Actually, line segments connecting two points corresponding to the control point and the bounding box of a trimming curve stream are found and the interference of these line segments and the bounding box is checked. In the case of interference as a result, it is regarded that the above area is included in the trim area, and the bounding box is generated from all points comprising this area, the control points on the generating curved surface correspondent thereto and control points comprising the trimming curve stream. When the curved surface is not the irrational trim curved surface, on the other hand, the bounding box is found while using projecting packing. While using these bounding boxes, interference line data are generated by an interference line generating means 4.;COPYRIGHT: (C)2001,JPO
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