opencv 仿射变换 计算旋转矩阵源码分析

/* Computes rotation_matrix matrix */
CVAPI(CvMat*)  cv2DRotationMatrix( CvPoint2D32f center, double angle,
double scale, CvMat* map_matrix );

CV_IMPL CvMat*
cv2DRotationMatrix( CvPoint2D32f center, double angle,
double scale, CvMat* matrix )
{
cv::Mat M0 = cv::cvarrToMat(matrix), M = cv::getRotationMatrix2D(center, angle, scale);
CV_Assert( M.size() == M.size() );
M.convertTo(M0, M0.type());
return matrix;
}

cv::Mat cv::getRotationMatrix2D( Point2f center, double angle, double scale )
{
angle *= CV_PI/180;
double alpha = cos(angle)*scale;
double beta = sin(angle)*scale;

Mat M(2, 3, CV_64F);
double* m = (double*)M.data;

m[0] = alpha;
m[1] = beta;
m[2] = (1-alpha)*center.x - beta*center.y;
m[3] = -beta;
m[4] = alpha;
m[5] = beta*center.x + (1-alpha)*center.y;

return M;
}