Store entries of vector<Point2d> as columns in eigen3 matrix

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Hello guys,

I'm fairly new to OpenCV and working with C++ in general, so I'm sorry if this seems trivial. The work I've already done is mostly the stuff covered in this tutorial:

http://docs.opencv.org/2.4/doc/tutori...

Now, I have a vector of Point2d, as generated in the Tutorial

      //-- Localize the object
  std::vector<Point2f> obj;
  std::vector<Point2f> scene;

  for( int i = 0; i < good_matches.size(); i++ )
  {
    //-- Get the keypoints from the good matches
    obj.push_back( keypoints_object[ good_matches[i].queryIdx ].pt );
    scene.push_back( keypoints_scene[ good_matches[i].trainIdx ].pt );
  }

Now, what I want to do is store these Points in a matrix given by the eigen3 Package for Bundle Adjustment. So I have initialised two matrices

void BundleAdjustment::feedMatches(const ImagePair& epair)
{
    // 2 x m eigen3 matrices storing P_i, P_j from vector<Point2d> format
    MatrixXd eP_i = MatrixXd(2, epair.P_i.size());
    MatrixXd eP_j = MatrixXd(2, epair.P_j.size());

So now, what I want to do, is take the two points I have in every entry of obj or scene and put them in the columns of the matrices eP_i and eP_j. How would I do that? Since the entries are of the type Point2d and not tupels of numbers, I cant seem to get the compiler to accept it. And I cant seem to recast it to another type either.

Any help would be appreciated!