DEVICE FOR COORDINATE TRANSFORMING CIRCULAR ARC BY APPROXIMATING IT AS CUBIC CURVE

摘要

PURPOSE:To improve the accuracy of an approximation by determining the coordinates of the four designated points of a tertiary curve to approximate a circular arc from midpoint passing conditions by the coordinate values of the center point of the circle of the circular arc and the start point and the termination point of the circular arc, the continuity of the start point and the termination point, and the symmetry of the circular arc. CONSTITUTION:The coordinate values of designated points P0-P3 of the cubic curve approximated at graphic drawing parts 3-6 can be obtained from the coordinate data of the center of the circle including the circular arc as input data, the coordinate value data of the start point of the circular arc, the coordinate value data of the termination point of the circular arc, or the radius of another circle calculable from these. Next, the coordinate values of designated points P0'-P3' which are respectively transformed into device coordinate systems using a linear transforming circuit 6 can be obtained. These coordinate values are processed by a vector processor 10 and stored in a page memory 11 so as to execute the curve drawing of the device coordinate systems. The contents of the page memory 11 are displayed on a display device through a mechanism control part 9. Thus, the arbitrary linear transformation of either the circle or the circular arc can be attained, and further, the accuracy of the approximation can be improved, and an approximation error can be decreased.