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c#c++opencvemgucv
hieu hoang
hieu hoang

Reputation: 1

How to use iterator in C# with EmguCV?

In OpenCV I use std::vector<std::vector<cv::Point>>::const_iterator like the code here:

std::vector<std::vector<cv::Point>> contours;
cv::findContours(contour,contours,CV_RETR_TREE,CV_CHAIN_APPROX_SIMPLE);    
std::vector<std::vector<cv::Point>>::const_iterator itContours = contours.begin();

while(itContours != contours.end())
{
    if(Condition1)
        itContours = contours.erase(itContours);
    else if(Condition2)
    itContours = contours.erase(itContours);
    else if(Condition3)
        itContours = contours.erase(itContours);
    else
        ++itContours;
}

But now I start using EmguCV but I can't find how to do like the code above. How can I do it?

Upvotes: 0

Views: 3201

Answers (1)

Chris
Chris

Reputation: 3482

Have a look at the shape detection example in the EMGU.Examples folder. It shows you how to deal with contours. I have copied the relevant code below for your reference but it's much better to have a look at the example.

        #region Find triangles and rectangles
        List<Triangle2DF> triangleList = new List<Triangle2DF>();
        List<MCvBox2D> boxList = new List<MCvBox2D>(); //a box is a rotated rectangle

        using (MemStorage storage = new MemStorage()) //allocate storage for contour approximation
           for (Contour<Point> contours = cannyEdges.FindContours(Emgu.CV.CvEnum.CHAIN_APPROX_METHOD.CV_CHAIN_APPROX_SIMPLE,        Emgu.CV.CvEnum.RETR_TYPE.CV_RETR_LIST, storage); contours != null; contours = contours.HNext)
           {
              Contour<Point> currentContour = contours.ApproxPoly(contours.Perimeter * 0.05, storage);

              if (currentContour.Area > 250) //only consider contours with area greater than 250
              {
                 if (currentContour.Total == 3) //The contour has 3 vertices, it is a triangle
                 {
                    Point[] pts = currentContour.ToArray();
                    triangleList.Add(new Triangle2DF(
                       pts[0],
                       pts[1],
                       pts[2]
                       ));
                 }
                 else if (currentContour.Total == 4) //The contour has 4 vertices.
                 {
                    #region determine if all the angles in the contour are within [80, 100] degree
                    bool isRectangle = true;
                    Point[] pts = currentContour.ToArray();
                    LineSegment2D[] edges = PointCollection.PolyLine(pts, true);

                    for (int i = 0; i < edges.Length; i++)
                    {
                       double angle = Math.Abs(
                          edges[(i + 1) % edges.Length].GetExteriorAngleDegree(edges[i]));
                       if (angle < 80 || angle > 100)
                       {
                          isRectangle = false;
                          break;
                       }
                    }
                    #endregion

                    if (isRectangle) boxList.Add(currentContour.GetMinAreaRect());
                 }
              }
           }
        #endregion

Let me know if you need any additional help and if any errors pop up,

Cheers,

Chris

Upvotes: 1

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