获取OpenCV中RotatedRect的绝对角度

opencv中RotatedRect的angle这个成员变量总是诡异的不同寻(http://stackoverflow.com/questions/15956124/minarearect-angles-unsure-about-the-angle-returned)，官网也没有任何解释。

下面是获取RotatedRect的绝对角度（0-180）的函数：

static double calcLineDegree(const Point2f& firstPt, const Point2f& secondPt)
{
    double curLineAngle = 0.0f;
    if (secondPt.x - firstPt.x != 0)
    {
        curLineAngle = atan(static_cast<double>(firstPt.y - secondPt.y) / static_cast<double>(secondPt.x - firstPt.x));
        if (curLineAngle < 0)
        {
            curLineAngle += CV_PI;
        }
    }
    else
    {
        curLineAngle = CV_PI / 2.0f; //90度
    }
    return curLineAngle*180.0f/CV_PI;
}
static double getRcDegree(const RotatedRect box)
{
    double degree = 0.0f;
    Point2f vertVect[4];
    box.points(vertVect);
    //line 1
    const double firstLineLen = (vertVect[1].x - vertVect[0].x)*(vertVect[1].x - vertVect[0].x) +
        (vertVect[1].y - vertVect[0].y)*(vertVect[1].y - vertVect[0].y);
    //line 2
    const double secondLineLen = (vertVect[2].x - vertVect[1].x)*(vertVect[2].x - vertVect[1].x) +
        (vertVect[2].y - vertVect[1].y)*(vertVect[2].y - vertVect[1].y);
    if (firstLineLen > secondLineLen)
    {
        degree = calcLineDegree(vertVect[0], vertVect[1]);
    }
    else
    {
        degree = calcLineDegree(vertVect[2], vertVect[1]);
    }
    return degree;
}

转载自：http://www.cnblogs.com/xylc/p/4269624.html