Why are the matrices not initialized/printed correctly? - c++

Question

I am playing around with cv::Mat and think my code really behaves weird, although I follow the syntax described in here.
Code:
std::cout << "parameter for matrices: " << "x = " << X << " y = " << Y << " psi = " << Psi << std::endl;
double dataRot[] = { cos(Psi), -sin(Psi), sin(Psi), cos(Psi) };
double dataTrans[] = { X, Y };
cv::Mat matRot(2, 2, CV_32FC1, dataRot);
cv::Mat matTrans(2, 1, CV_32FC1, dataTrans);
std::cout << "matRot = " << matRot.at<double>(0,0) << "," << matRot.at<double>(0,1) << ";" << matRot.at<double>(1,0) << "," << matRot.at<double>(1,1) << std::endl;
std::cout << "matRot = " << matRot << std::endl;
std::cout << "matTrans = " << matTrans.at<double>(0,0) << "," << matTrans.at<double>(0,1) << std::endl;
std::cout << "matTrans = " << matTrans << std::endl;
matOut = matRot*matIn + matTrans*cv::Mat::ones(1, matIn.cols, CV_32FC1);
Output:
parameter for matrices: x = 20.5 y = 20 psi = 0
matRot = 1,-0;-0,0
matRot = [0, 1.875;
0, -0]
matTrans = 20.5,20
matTrans = [0; 2.8203125]
Why is the identity matrix not initalized correctly?
And why does the second way of printing a matrix deliver wrong results?
Any help is appreciated.

Answer 1

Since you're working with double, the OpenCV matrix type should be CV_64FC1:
cv::Mat matRot(2, 2, CV_64FC1, dataRot);
cv::Mat matTrans(2, 1, CV_64FC1, dataTrans);
For simplicity, you can also use:
cv::Matx22d matRot(cos(Psi), -sin(Psi), sin(Psi), cos(Psi));
cv::Matx21d matTrans(X, Y);
or:
cv::Mat1d matRot = (cv::Mat1d(2,2) << cos(Psi), -sin(Psi), sin(Psi), cos(Psi));
cv::Mat1d matTrans = (cv::Mat1d(2,1) << X, Y);
and access values like:
std::cout << matRot(row, col);