计算直线角度

根据theta = atan(dy / dx) 求取角度

float computeAngle(CvPoint pt0, CvPoint pt1){int dx = pt1.x - pt0.x;int dy = pt1.y - pt0.y;if(dx == 0){if(dy < 0){return CV_PI / 2.0;}else if(dy > 0){return -CV_PI / 2.0;}else{return 0.0;}}return atanf((float)dy / dx);}