Using a Queue to keep Translation and Rotational Matrices in OpenCV

Question

I need to use a Queue to keep rotation and translation matrices generated (using cvFindExtrinsicCameraParams2()) for each contour.

But when I pop elements from the queue all I can get is copies of the same pair of rotation and translation.

I doubt it has something to do with pointers, but when I tried to avoid pointers in the struct, the cvFindExtrinsicCameraParams2() threw an Exception. How to fix this?

//------------A.h------------------
struct RotMat{
    CvMat *rotation_;
    CvMat *translation_;
};


//-----------B.h-------------------
class B {

private:
        CvMat *rotation;
        CvMat *translation;
} 


//-----------B.cpp-----------------
#include "A.h"
#include "B.h"

void functionx(){

        queue<RotMat> rtq;

        // start loop

                // cvFindExtrinsicCameraParams2(&object_points,&image_points,
                //                               intrinsic,distortion,
                //                                rotation,translation);

                RotMat rt = {rotation, translation};
                rtq.push(rt);

        // end loop

        while(!rtq.empty()) { //assume rtq has n elements

                RotMat rt_ = rtq.front();
                rtq.pop();
                cout<< rt_.translation_->data.fl[1]; // the same value pair is 
                cout<< rt_.rotation->data.fl[1];     // printed in all n iterations

        } 
}

Test Results

Total markers detected = 2

Marker 1: Translation: -249.227
          Rotation: -0.0124926

Marker 2: Translation: -249.227
          Rotation: -0.0124926

Answer 1

You are pushing pointers into the queue, but you are reusing the same memory locations. So, all of your queue items are pointing to the same location in memory.

Create new rotation and translation matrices before calling cvFindExtrinsicCameraParams2. Then push the newly created matrix pointers onto the queue.

You may want to look at using smart pointers, so you don't have memory leak issues. Or, just use the Mat class, and let it manage the data for you.