说明：  开源多边形计算GPC的修改版，可以添加到VC工程中直接调用。该库功能：计算多边形面积，顶点查找，边查找，计算多边形之间的交、并、或、补等各种操作，对于数值、图形图像处理非常有用。
(Open-source computing GPC polygon modified version, can be added to the VC works directly call. The library features: calculating polygon area, vertex find, side to find, the calculation of the settlement between the polygon and, or, fill a variety of operations, for the value, graphics, image processing very useful.)