Sending data from OpenCV matrix to Matlab Engine, C++

Question

I am sending data from OpenCV matrices to matlab using C++ and Matlab Engine. I tried to convert from column major to row major but I am really confused on how to do that. I cannot understand how to deal with Matlab pointer mxArray and put data to the engine.

Has anybody worked with OpenCV together with matlab to send matrices? I didn't find much information and I think it is a really interesting tool. Any help will be welcomed.

Galton

worth checking out mexopencv, a project exposing OpenCV to MATLAB as MEX-functions – Wapiti

Answer 1

I have a function that works if you have created the matlab engine. What I do is creating a SingleTone template for the matlab engine:

My header looks like this:

/** Singletone class definition
  * 
  */
class MatlabWrapper
    {
    private:
        static MatlabWrapper *_theInstance; ///< Private instance of the class
        MatlabWrapper(){}           ///< Private Constructor
        static Engine *eng; 

    public:
        static MatlabWrapper *getInstance() ///< Get Instance public method
        {
            if(!_theInstance) _theInstance = new MatlabWrapper(); ///< If instance=NULL, create it

    return _theInstance;            ///< If instance exists, return instance
        }
    public:
    static void openEngine();               ///< Starts matlab engine.
    static void cvLoadMatrixToMatlab(const Mat& m, string name);
    };

My cpp:

#include <iostream>
using namespace std;

MatlabWrapper *MatlabWrapper::_theInstance = NULL;              ///< Initialize instance as NULL    
Engine *MatlabWrapper::eng=NULL;
void MatlabWrapper::openEngine()
{
        if (!(eng = engOpen(NULL))) 
        {
            cerr << "Can't start MATLAB engine" << endl;
            exit(-1);
        }       
}
void MatlabWrapper::cvLoadMatrixToMatlab(const Mat& m, const string name)
{
    int rows=m.rows;
    int cols=m.cols;    
    string text;
    mxArray *T=mxCreateDoubleMatrix(cols, rows, mxREAL);

    memcpy((char*)mxGetPr(T), (char*)m.data, rows*cols*sizeof(double));
    engPutVariable(eng, name.c_str(), T);
    text = name + "=" + name + "'";                    // Column major to row major
    engEvalString(eng, text.c_str());
    mxDestroyArray(T);
}

When you want to send a matrix, for example

Mat A = Mat::zeros(13, 1, CV_32FC1);

It's so simple as this:

MatlabWrapper::getInstance()->cvLoadMatrixToMatlab(A,"A");

Yan