How to get vertex index from Subdiv2D Delaunay triangulation

Question

I am using OpenCV 3.1 and want to know how to get the vertex index of an edge in Subdiv2D Delaunay triangulation, not only the vertex coordinates? I want to use this index to keep the vertex value for further interpolation.

For example:

cv::Subdiv2D subdiv(rect);
// Insert some points to subdiv....
cv::Point2f org, dst;
subdiv.edgeOrg(edge, &org); // starting point of edge

This gives me only the coordinates of the vertex in org.

I've seen that in OpenCV 2.4, we could use the CvSubdiv2DPoint type, which held the id in addition to the standard Point32f. In OpenCV 3.1, I can't find this struct and it looks like it had been removed for some reason.

Answer 1

If any one else look at that question. You can create a class that herits from subdiv2D and implement your own function that returns index this way:

.h

#ifndef __Subdiv2DIndex__
#define __Subdiv2DIndex__

#include <vector>
#include <opencv2\opencv.hpp>
using namespace cv;

class Subdiv2DIndex : public Subdiv2D
{
public :
  Subdiv2DIndex(Rect rectangle);

  //Source code of Subdiv2D: https://github.com/opencv/opencv/blob/master/modules/imgproc/src/subdivision2d.cpp#L762
  //The implementation tweaks getTrianglesList() so that only the indice of the triangle inside the image are returned
  void getTrianglesIndices(std::vector<int> &ind) const;
};

#endif

.cpp #include "Subdiv2DIndex.h"

Subdiv2DIndex::Subdiv2DIndex(Rect rectangle) : Subdiv2D{rectangle}
{
}

void Subdiv2DIndex::getTrianglesIndices(std::vector<int> &triangleList) const
{
  triangleList.clear();
  int i, total = (int)(qedges.size() * 4);
  std::vector<bool> edgemask(total, false);
  const bool filterPoints = true;
  Rect2f rect(topLeft.x, topLeft.y, bottomRight.x - topLeft.x, bottomRight.y - topLeft.y);

  for (i = 4; i < total; i += 2)
  {
    if (edgemask[i])
      continue;
    Point2f a, b, c;
    int edge_a = i;
    int indexA = edgeOrg(edge_a, &a) -4;
    if (filterPoints && !rect.contains(a))
      continue;
    int edge_b = getEdge(edge_a, NEXT_AROUND_LEFT);
    int indexB = edgeOrg(edge_b, &b) - 4;
    if (filterPoints && !rect.contains(b))
      continue;
    int edge_c = getEdge(edge_b, NEXT_AROUND_LEFT);
    int indexC = edgeOrg(edge_c, &c) - 4;
    if (filterPoints && !rect.contains(c))
      continue;
    edgemask[edge_a] = true;
    edgemask[edge_b] = true;
    edgemask[edge_c] = true;

    triangleList.push_back(indexA);
    triangleList.push_back(indexB);
    triangleList.push_back(indexC);
  }
}

Answer 2

So turned out that in OpenCV 3 some of the functions in cv::Subdiv2D which were void now returns an integer. In my case I found out that subdiv.edgeOrg(...) and subdiv.edgeDst(...) returns the vertex id as integer.