求两直线交点

转自 http://blog.youkuaiyun.com/yangtrees/article/details/7965983

struct Line  
{  
	CvPoint p1,p2;  
	double a,b,c;  
};  

void GetLinePara(Line &l)  
{  
	l.a=l.p1.y-l.p2.y;  
	l.b=l.p2.x-l.p1.x;  
	l.c=l.p1.x*l.p2.y-l.p1.y*l.p2.x;  
}  

CvPoint getCrossPoint(Line &l1,Line &l2)  
{  
	GetLinePara(l1);  
	GetLinePara(l2);  
	double D=l1.a*l2.b-l2.a*l1.b;    
	CvPoint p;    
	p.x=(l1.b*l2.c-l2.b*l1.c)/D;    
	p.y=(l1.c*l2.a-l2.c*l1.a)/D;    
	return p;   
}