如何在 OpenCVSharp 中使用 OutputArray？

Question

I am trying to use the function Cv2.ApproxPolyDP in OpenCVSharp. It should return a List<Point> ( Vector<Point> in C++) for the approxCurve parameter. This parameter is of type OutputArray . I can't seem to make heads or tails of that, and documentation is sparse.

There seems to be no constructor for an OutputArray nor can I convert one to a List<Point> . Can someone let me know (preferably with code) how I can call Cv2.ApproxPolyDP and get a List<Point> back for the approxCurve parameter?

Thanks!

Answer 1

The current version says "The type should match the type of the input curve".

You should be able to convert the OutputArray to a Mat, and then use ToArray() to get the list of points.

Does this work?

OutputArray output;
Cv2.ApproxPolyDP(..., output, ...);
var list = output.ToMat().ToArray();

Edit: Just realised ToArray() is an extension method we wrote. This may help (without the conversion to CV_64F).

    public static double[,] To2DArray(this Mat mat)
    {
        mat.ConvertTo(mat, MatType.CV_64F);
        if (mat.Rows <= 1)
        {
            m_Log.WarnFormat("1D Mat converted to 2D array, size={0}x{1}", mat.Rows, mat.Cols);
        }
        double[,] arr = new double[mat.Rows, mat.Cols];
        mat.GetArray(0, 0, arr);

        return arr;
    }

    public static double[] ToArray(this Mat mat)
    {
        double[,] array2d = mat.To2DArray();

        int rowCount = array2d.GetLength(0);

        double[] array = new double[rowCount];
        for (int i = 0; i < rowCount; i++)
        {
            array[i] = array2d[i, 0];
        }
        return array;
    }