CAD二次开发判断点是否在一个多段线区域内

通过几何拓展类来计算点是否在多段线内
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Given two line segments (p1, q1) and (p2, q2), find if the given line segments intersect with each other.
Before we discuss solution, let us define notion of orientation. Orientation of an ordered triplet of points in the plane can be
–counterclockwise
–clockwise
–collinear

The following diagram shows different possible orientations of (a, b, c)
How is Orientation useful here?
Two segments (p1,q1) and (p2,q2) intersect if and only if one of the following two conditions is verified

1. General Case:
   – (p1, q1, p2) and (p1, q1, q2) have different orientations and
   – (p2, q2, p1) and (p2, q2, q1) have different orientations.

Examples:

2. Special Case
– (p1, q1, p2), (p1, q