如何判断一个线相交在C＃中的多边形？ [英] How to tell if a line intersects a polygon in C#?

问题描述

我有一个问题非常类似： <一href="http://stackoverflow.com/questions/30080/how-to-know-if-a-line-intersects-a-plane-in-c-basic-2d-geometry">http://stackoverflow.com/questions/30080/how-to-know-if-a-line-intersects-a-plane-in-c-basic-2d-geometry

I have a question very similar to this: http://stackoverflow.com/questions/30080/how-to-know-if-a-line-intersects-a-plane-in-c-basic-2d-geometry

我正在寻找一种方法，告诉如果一条线相交的任意多边形在C＃。

I am searching for a method that tells if a line is intersecting an arbitrary polygon in C#.

我觉得从克里斯 - marasti - 格奥尔格·算法是非常有益的，但​​是缺少最重要的方法 - 线对线相交

I think the algorithm from chris-marasti-georg was very helpful but missing the most important method - line to line intersection.

有谁知道的交线的方法来完成克里斯Marasti - 乔格的code或有什么相似？

Does anyone know of a line intersection method to complete Chris Marasti-Georg's code or have anything similar?

有没有在C＃中内置的code这个？

Is there a built-in code for this in c#?

这方法是与Bing地图算法，增强了禁区功能的使用。由此产生的路径不能穿过禁区（任意多边形）。

This method is for use with the Bing Maps algorithm enhanced with a forbidden area feature. The resulting path must not pass through forbidden area (the arbitrary polygon).

感谢您！ /埃里克

推荐答案

没有内建code的边缘检测内置在.NET框架。

There is no builtin code for edge detection built into the .NET framework.

下面是code（移植到C＃），做你所需要的（实际的算法是在comp.graphics.algorithms发现在谷歌组）：

Here's code (ported to C#) that does what you need (the actual algorithm is found at comp.graphics.algorithms on Google groups) :

public static PointF FindLineIntersection(PointF start1, PointF end1, PointF start2, PointF end2)
{
	float denom = ((end1.X - start1.X) * (end2.Y - start2.Y)) - ((end1.Y - start1.Y) * (end2.X - start2.X));

	//  AB & CD are parallel 
	if (denom == 0)
		return PointF.Empty;

	float numer = ((start1.Y - start2.Y) * (end2.X - start2.X)) - ((start1.X - start2.X) * (end2.Y - start2.Y));

	float r = numer / denom;

	float numer2 = ((start1.Y - start2.Y) * (end1.X - start1.X)) - ((start1.X - start2.X) * (end1.Y - start1.Y));

	float s = numer2 / denom;

    if ((r < 0 || r > 1) || (s < 0 || s > 1))
		return PointF.Empty;

	// Find intersection point
	PointF result = new PointF();
	result.X = start1.X + (r * (end1.X - start1.X));
	result.Y = start1.Y + (r * (end1.Y - start1.Y));

	return result;
 }

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