...做法如下：在坐标平面（我们先从平面入手）上，取定“点偶”（point pair）(P，Q)，称其为“有向线段”（directed line segment），P为“始点”，Q为”终点“，记为PQ。
双语例句
1
The intersection of sweep volume with complicated surface normal is transformed into computation of intersection between triangular mesh and directedlinesegment.
将扫描体与复杂曲面法矢的求交问题，转化为三角网格与有向线段之间的求交计算。
2
The cutter is directed to move along each linesegment one by one in order to generate the smooth circular path.