旋转cv :: Rect的中心 [英] Center of rotated cv::Rect
问题描述
我有一个图像,并且在图像上放置了一个矩形.然后,我旋转图像.如何获得旋转图像上矩形的中心?
I have an image, and I place a rectangle on the image. Then I rotate the image. How do I get the center of the rectangle on the rotated image?
或者我可以以某种方式旋转矩形以放置旋转后的图像吗?我认为在这种情况下,旋转必须与用于旋转图像的点沿着同一点进行.
Or can I rotate a rectangle somehow to put on rotated image? I think in this case rotation must be done along same point with point used to rotate image.
这是上面放有矩形的图像.
This is the image with a rectangle placed on it.
这是旋转的图像.
这是我用来旋转图片的代码:
Here is the code I use to rotate my image:
cv::Mat frame, frameRotated;
frame = cv::imread("lena.png");
cv::Rect rect(225,250,150,150);
cv::rectangle(frame, rect, cv::Scalar(0,0,255),2);
int theta = 30;
double radians = theta * PI / 180.0;
double sin = abs(std::sin(radians));
double cos = abs(std::cos(radians));
int newWidth = (int) (frame.cols * cos + frame.rows * sin);
int newHeight = (int) (frame.cols * sin + frame.rows * cos);
cv::Mat targetMat(cv::Size(newWidth, newHeight), frame.type());
int offsetX = (newWidth - frame.cols) / 2;
int offsetY = (newHeight - frame.rows) / 2;
frame.copyTo(targetMat.rowRange(offsetY, offsetY + frame.rows).colRange(offsetX, offsetX + frame.cols));
cv::Point2f src_center(targetMat.cols/2.0F, targetMat.rows/2.0F);
cv::Mat rot_mat = cv::getRotationMatrix2D(src_center, theta, 1.0);
cv::warpAffine(targetMat, frameRotated, rot_mat, targetMat.size());
imshow("frame", frame);
imshow("rotated frame", frameRotated);
编辑
假设旋转的图像中有一个点,如何使用旋转矩阵在原始图像中获得对应的点?
Suppose I have a point in the rotated image, how do I get corresponding point in the original image using rotation matrix?
推荐答案
您只需要使用rot_mat来变换矩形的原始中心.我测试了以下内容,并且可以正常工作:
You only need to use rot_mat to transform the original center of the rect. I tested the below and it works:
cv::Rect r(250, 350, 20, 30);
cv::Point2d c(r.x + r.width / 2, r.y + r.height / 2);
// c is center of rect
// get c's location in targetMat when frame is copied
c.x += offsetX;
c.y += offsetY;
int theta = 30;
double radians = theta * M_PI / 180.0;
cv::Point2d src_center(targetMat.cols/2.0F, targetMat.rows/2.0F);
cv::Mat rot_mat = cv::getRotationMatrix2D(src_center, theta, 1.0);
// now transform point using rot_mat
double *x = rot_mat.ptr<double>(0);
double *y = rot_mat.ptr<double>(1);
Point2d dst(x[0] * c.x + x[1] * c.y + x[2],
y[0] * c.x + y[1] * c.y + y[2]);
// dst is center of transformed rect
编辑
要从旋转的图像中变换一个点,您只需要逆转该过程即可:
To transform a point from the rotated image you just need to reverse the process:
// undo translation
Point2d dst1(dst.x - x[2], dst.y - y[2]);
// undo rotation
Point2d dst2(x[0] * dst1.x - x[1] * dst1.y, -y[0] * dst1.x + y[1] * dst1.y);
// undo shift
Point2d in_unrotated_image(dst2.x - offsetX, dst2.y - offsetY);
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