| 摘要 |
PURPOSE:To specify the start point and end point of a straight line even unless control points are in a line if two-dimensional B-spline curve data obtained from three-dimensional B-spline curve data through dimension conversion indicate a straight line. CONSTITUTION:In S1, control point information and knot vectors being the basic data of the three-dimensional B-spline curve data are inputted and a projecting method, a conversion matrix, etc., are inputted. In S2, the conversion matrix is used to convert the three-dimensional spline curve data into the two-dimensional B-spline curve data. When it is decided that the shape is a straight line in S3, the coefficients of a curve definition polynomial by control point sections are found in S5, maximum and minimum values of (x) in the respective control point sections are found in S5, and values (y) corresponding to the maximum and minimum values of (x) in all the control point sections are found in S6. Then the maximum and minimum values of (x) in all the control point sections and the values (y) corresponding to them are stored in a memory as straight line data showing the start and end points of the straight line in S7. |
