matrix multiplication in Opencv using c++ - c++

Question

Hi all I'm a rookie in C++ and Opencv as well. Kindly help me out on this.
I have a function (cv::aruco::estimatePoseSingleMarkers(markerCorners, markerLength, camMatrix, distCoeffs, rvecs,tvecs); that gives pose of the marker w.r.t camera.
I used a for loop to print out the values of tvecs from the function.
tvecs: [-0.0240248, 0.0161165, 0.052999]
When I print the size of tvecs it says the size is 1. But I think itś 1x3.
My requirement is to perform a matrix multiplication of the above mentioned tvces and a matrix of size [3x3].
How do I do this?
The following is the piece of code:
// Get frame and convert to OpenCV Mat
int openCVDataType=CV_8UC3;
cv::Mat image(cv::Size(pRequest->imageWidth.read(),pRequest->imageHeight.read()),openCVDataType,pRequest->imageData.read(),pRequest->imageLinePitch.read() );
//Undistort
cv::remap(image, imageUndist, map1, map2, CV_INTER_LINEAR);
//ArUco detection
cv::aruco::detectMarkers(imageUndist,dictionary,markerCorners,markerIds,detectorParams,rejectedCandidates);
if(markerIds.size() > 0) {
cv::aruco::estimatePoseSingleMarkers(markerCorners, markerLength, camMatrix, distCoeffs, rvecs,tvecs);
for(unsigned int d = 0;d<markerIds.size();d++) {
cout<<"tvecsss: "<<tvecs[d]<<endl;
cout<<"tvecs: "<<tvecs[d].t()<<endl;
cv::Mat rotMat;
cv::Rodrigues(rvecs[d],rotMat);
rotMat = rotMat.t();
cout<<"rotMat: "<<rotMat<<endl;
cout<<"translation: "<<-tvecs[d]*rotMat<<endl;
}
There's an error when I multiply tvecs[d]*rotMat. This the error:
mat.inl.hpp:1274: error: (-215:Assertion failed) data && dims <= 2 &&
(rows == 1 || cols == 1) && rows + cols - 1 == n && channels() == 1 in
function 'operator cv::Vec<_Tp, m>'

Answer 1

You need to change this:
-tvecs[d]*rotMat
into this:
rotMat*-tvecs[d]
Tvec is 3x1 matrix and rotMat is 3x3 matrix