Read dataset

cv::FileStorage fs("viff.xml", cv::FileStorage::READ);
for (int i=0; i<36; i++) {
  std::stringstream smat;
  cv::Mat P;
  smat << "viff" << std::setfill('0') << std::setw(3) << i << "_matrix";
  fs[smat.str()] >> P;
}