C#结合余弦定理计算两条Polyline多段线的夹角

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已知两条多段线（每条多段线只由两个点组成）有一个共点，求其角度，验证是否大于指定角度（默认90度）。

代码如下：

private bool ValidateAngle(IPolyline pFromPolyline, IPolyline pToPolyline, double dMinAngle = 90)
{
	var bValid = true;
	try
	{
		var pPointB1 = pFromPolyline.ToPoint;
		var pPointB2 = pToPolyline.FromPoint;
		if (CalculateDistance(pPointB1, pPointB2) > 1e-5)
			throw new Exception("传入了两条不共点的线段");
		var pPointB = pPointB1;

		var pPointA = pFromPolyline.FromPoint;
		var pPointC = pToPolyline.ToPoint;

		var a = CalculateDistance(pPointB, pPointC);
		var b = CalculateDistance(pPointA, pPointC);
		var c = CalculateDistance(pPointA, pPointB);

		var cosB = (a * a + c * c - b * b) / (2 * a * c);
		double dAngle = 180 / Math.PI * Math.Acos(cosB); //弧度转角度
		if (dAngle < dMinAngle)
		{
			bValid = false;
		}
	}
	catch
	{
		bValid = false;
	}
	return bValid;
}