convert armadillo data to other types of data

armadillo to other data format conversion

Armadillo is a C++ linear algebra library, especially for computer vision application.

Armadillo is more similar to MATLAB with decent performance. (check http://nghiaho.com/?p=1726 for comparison).

We may want to cooperate Armadillo with OpenCV, STL or FFTW. In this blog the conversion between STL and OpenCV will be described.

1. armadillo to STL vector

int nRow = 4;

int nCol = 5;

arma::mat A = arma::randu<arma::mat>(nRow, nCol);

std::cout << " arma::mat A: " << A << std::endl;

arma::mat tmpA = A.t();

 

std::vector< std::vector<double> > Vec;

Vec.resize(nRow);

     

for (int i = 0; i < nRow; i++) {

    // initialize tmpVec by input A data pointer

    std::vector<double> tmpVec( tmpA.colptr(i), tmpA.colptr(i) + nCol);

    Vec[i] = tmpVec;

}

 

std::cout << " A to tmpA conversion: " << std::endl;

BOOST_FOREACH(std::vector<double> tmpVec, Vec){

    BOOST_FOREACH(double d, tmpVec){

        std::cout << d << " ";

    }

    std::cout << std::endl;

}

}

2. Armadillo to OpenCV, Since OpenCV data is saved in row-wised, and armadillo data is saved in column-wised, therefore, when we convert the data, we may need to do transformation at first. The following is the sample code.

// -----------------------------

// arma::mat to opencv

// -----------------------------

cv::Mat img(2, 2, CV_32FC1);

cv::randu(img, cv::Scalar(0), cv::Scalar(255));

     

std::cout << "img Test" << img << std::endl;

cv::Mat imgt(img.t());

     

// mat to armadillo

arma::fmat armaConv(imgt.ptr<float>(), 2, 2);

std::cout << "armaConv" << std::endl << armaConv << std::endl;

}

3. OpenCV to Armadillo

// armadillo to mat

arma::fmat arma2matData = arma::randu<arma::fmat>(5, 6);

std::cout << "arma2matData: " << std::endl << arma2matData << std::endl;

     

cv::Mat cvMatConvTmp(6, 5, CV_32FC1, arma2matData.memptr());

cv::Mat cvMatConv(cvMatConvTmp.t());

std::cout << "cvMatConv: " << std::endl << cvMatConv << std::endl;

}

4. STL 2D vector (vector<vector<T> >) to Opencv cv::Mat 2D matrix

template <typename T>

cv::Mat_<t> vec2cvMat_2D(std::vector< std::vector<T> > &inVec){

  int rows = static_cast<int>(inVec.size());

 int cols = static_cast<int>(inVec[0].size());

  

 cv::Mat_<t> resmat(rows, cols);

 for (int i = 0; i < rows; i++)

 {

  resmat.row(i) = cv::Mat(inVec[i]).t();

 }

 return resmat;

}

origin blog address:http://dragonwood-blastevil.blogspot.com/2013/04/armadillo-to-other-data-format.html