cv::RotatedRect::points误差较大

最后发现不是point的精度问题，float不至于产生这么大误差，是自己代码里缓存了顶点坐标，后面由手动修改了旋转矩形的角度，导致不匹配！

下文可以忽略了-_-!

发现一个天坑，通过高宽和角度构造了一个旋转矩形

RotatedRect(const Point2f& _center, const Size2f& _size, float _angle)

然后通过points返回矩形的四个顶点

void points(Point2f pts[])

发现这些顶点跟构造时的角度差距较大

如旋转矩形
center={x=1852.00000 y=560.000000 }
size={width=380.000000 height=132.000000 }
angle=39.6590843

points返回的点集

•   [0]	{x=1669.15649 y=476.189209 }	cv::Point_<float>
  

•   [1]	{x=1760.48804 y=380.886719 }	cv::Point_<float>
  

•   [2]	{x=2034.84351 y=643.810791 }	cv::Point_<float>
  

•   [3]	{x=1943.51196 y=739.113281 }	cv::Point_<float>
  

求点1和点2的角度 （matlab）

p0 = [2034.84351 643.810791];
p1 = [1760.48804 380.886719];
atan((p0(2) -  p1(2)) /  (p0(1) -  p1(1))) / pi * 180;

ans = 43.781133464613490
差了令人瞩目的4.1220，所以要做变换矩阵的计算时慎用，会带来很大的误差！

查看points源码
sources\modules\core\src\matrix.cpp

void RotatedRect::points(Point2f pt[]) const
{
    double _angle = angle*CV_PI/180.;
    float b = (float)cos(_angle)*0.5f;
    float a = (float)sin(_angle)*0.5f;

    pt[0].x = center.x - a*size.height - b*size.width;
    pt[0].y = center.y + b*size.height - a*size.width;
    pt[1].x = center.x + a*size.height - b*size.width;
    pt[1].y = center.y - b*size.height - a*size.width;
    pt[2].x = 2*center.x - pt[0].x;
    pt[2].y = 2*center.y - pt[0].y;
    pt[3].x = 2*center.x - pt[1].x;
    pt[3].y = 2*center.y - pt[1].y;
}

重写一个基于double运算的版本，算出来的角度就对了

void MyGetVertices(cv::Point2d pt[4], cv::RotatedRect &rect)
	{		
		double _angle = rect.angle*CV_PI / 180.;
		double b = cos(_angle)*0.5;
		double a = sin(_angle)*0.5;

		cv::Point2f center = rect.center;
		cv::Size2f size = rect.size;
		pt[0].x = center.x - a*size.height - b*size.width;
		pt[0].y = center.y + b*size.height - a*size.width;
		pt[1].x = center.x + a*size.height - b*size.width;
		pt[1].y = center.y - b*size.height - a*size.width;
		pt[2].x = 2 * center.x - pt[0].x;
		pt[2].y = 2 * center.y - pt[0].y;
		pt[3].x = 2 * center.x - pt[1].x;
		pt[3].y = 2 * center.y - pt[1].y;
	}

返回的点集如下

•   [0]	{x=1663.6050505562603 y=489.54900267497470 }	cv::Point_<double>
  

•   [1]	{x=1747.8498550961431 y=387.92807516475688 }	cv::Point_<double>
  

•   [2]	{x=2040.3949494437397 y=630.45099732502536 }	cv::Point_<double>
  

•   [3]	{x=1956.1501449038569 y=732.07192483524318 }	cv::Point_<double>