一个具有动态捕捉功能的简易2dCAD系统，能灵活绘制一般的简单图形，同时能检测多边形的方向和凹凸性以及点和多边形的关系-A simple 2d CAD dynamic capture system, the flexibility to draw simple graphics in general, but can detect the direction and the concave and convex polygons, and the relationship between poi