Abstract: The graphics input apparatus enables an operator to input a two or three-dimensional schematic figure into a computer simply by hand-writing a two-dimensioanl figure in a picture plane of a display device such as a cathode ray tube. The graphics input apparatus is provided with a display device, a memory, a position indicator for indicating predetermined positions in the picture plane of the display device, and a cursor display for displaying a cursor at the position indicated by the position indicator.

Abstract: A curvilinear interpolation system and method for use in a numerical control apparatus such as a machine tool or a robot having two or more drive axes and movable while effecting linear interpolation on a given curve with a plurality of line segments. For each line segment a curvature K.sub.p of the curve is calculated at a current curve interpolating point P.sub.p, and a curvature K.sub.n calculated at a point P.sub.n on the curve spaced a given search length l.sub.S from the point P.sub.p along the curve. Then, a curvature K.sub.s is set equal to K.sub.p when K.sub.p .gtoreq.K.sub.n and set equal to K.sub.n when K.sub.p <K.sub.n. The curvature K.sub.s is compared with a limit curvature K.sub.L established for determining whether a curve portion is a straight line or an arc for establishing the curve portion as an arc having the curvature K.sub.s when K.sub.s .gtoreq.K.sub.