O código a seguir está funcionando corretamente para quadrados, mas não funciona no triângulo. Por quê?

Aqui está o meu código de exemplo:

public void onClick(View v) {

            ImageView resim = (ImageView)findViewById(R.id.imgview_gosterge);
            Bitmap image=((BitmapDrawable)resim.getDrawable()).getBitmap();
            Bitmap bmp32 = image.copy(Bitmap.Config.ARGB_8888, true);

            Mat tmp = new Mat (bmp32.getHeight(), bmp32.getWidth(), CvType.CV_8U);
            //Utils.bitmapToMat(image, tmp);
            Utils.bitmapToMat(bmp32, tmp);

            bmp32.recycle();

            Imgproc.cvtColor(tmp, tmp, Imgproc.COLOR_RGB2HSV, 4 );

            tmp = findLargestRectangle(tmp);

            Bitmap bmp = Bitmap.createBitmap(tmp.cols(), tmp.rows(), Bitmap.Config.ARGB_8888);
            Utils.matToBitmap(tmp, bmp);

            //Utils.matToBitmap(tmp, image);

            ImageView resim2 = (ImageView)findViewById(R.id.imgview_gosterge2);
            resim2.setImageBitmap(bmp);



        }
    });

findLargestRectangle:

findLargestRectangle(Mat original_image) {
        Mat imgSource = original_image;
            //Mat untouched = original_image.clone();
    //convert the image to black and white
    Imgproc.cvtColor(imgSource, imgSource, Imgproc.COLOR_BGR2GRAY);

    //convert the image to black and white does (8 bit)
    Imgproc.Canny(imgSource, imgSource, 50, 50);

    //apply gaussian blur to smoothen lines of dots
    Imgproc.GaussianBlur(imgSource, imgSource, new Size(5, 5), 5);

    //find the contours
    List<MatOfPoint> contours = new ArrayList<MatOfPoint>();
    Imgproc.findContours(imgSource, contours, new Mat(), Imgproc.RETR_LIST, Imgproc.CHAIN_APPROX_SIMPLE);

    double maxArea = -1;
    int maxAreaIdx = -1;
    MatOfPoint temp_contour = contours.get(0); //the largest is at the index 0 for starting point
    MatOfPoint2f approxCurve = new MatOfPoint2f();
    MatOfPoint2f maxCurve = new MatOfPoint2f();
    List<MatOfPoint> largest_contours = new ArrayList<MatOfPoint>();
    for (int idx = 0; idx < contours.size(); idx++) {
        temp_contour = contours.get(idx);
        double contourarea = Imgproc.contourArea(temp_contour);
        //compare this contour to the previous largest contour found
        if (contourarea > maxArea) {
            //check if this contour is a square
            MatOfPoint2f new_mat = new MatOfPoint2f( temp_contour.toArray() );
            int contourSize = (int)temp_contour.total();
            Imgproc.approxPolyDP(new_mat, approxCurve, contourSize*0.05, true);
            if (approxCurve.total() == 4) {
                maxCurve = approxCurve;
                maxArea = contourarea;
                maxAreaIdx = idx;
                largest_contours.add(temp_contour);
            }
        }
    }


 //create the new image here using the largest detected square
        Mat new_image = new Mat(imgSource.size(), CvType.CV_8U); //we will create a new black blank image with the largest contour
        Imgproc.cvtColor(new_image, new_image, Imgproc.COLOR_BayerBG2RGB);
        Imgproc.drawContours(new_image, contours, maxAreaIdx, new Scalar(255, 255, 255), 1); //will draw the largest square/rectangle


    System.out.println("points length" + temp_contour.toArray().length);

    if( temp_contour.toArray().length == 5)
    {
        System.out.println("Pentagon");
        TextView temp_text = (TextView)findViewById(R.id.temp_text);
        temp_text.setText("\n Beşgen");

    }
    else if(temp_contour.toArray().length > 5)
    {
        System.out.println("Circle");
        TextView temp_text = (TextView)findViewById(R.id.temp_text);
        temp_text.setText("\n Daire");
    }
    else if(temp_contour.toArray().length == 4)
    {
        System.out.println("Square");

        double temp_double[] = maxCurve.get(0, 0);
        Point p1 = new Point(temp_double[0], temp_double[1]);
        Imgproc.circle(new_image, new Point(p1.x, p1.y), 20, new Scalar(255, 0, 0), 5); //p1 is colored red
        String temp_string = "Point 1: (" + p1.x + ", " + p1.y + ")";


        temp_double = maxCurve.get(1, 0);
        Point p2 = new Point(temp_double[0], temp_double[1]);
        Imgproc.circle(new_image, new Point(p2.x, p2.y), 20, new Scalar(0, 255, 0), 5); //p2 is colored green
        temp_string += "\nPoint 2: (" + p2.x + ", " + p2.y + ")";

        temp_double = maxCurve.get(2, 0);
        Point p3 = new Point(temp_double[0], temp_double[1]);
        Imgproc.circle(new_image, new Point(p3.x, p3.y), 20, new Scalar(0, 0, 255), 5); //p3 is colored blue
        temp_string += "\nPoint 3: (" + p3.x + ", " + p3.y + ")";

        temp_double = maxCurve.get(3, 0);
        Point p4 = new Point(temp_double[0], temp_double[1]);
        Imgproc.circle(new_image, new Point(p4.x, p4.y), 20, new Scalar(0, 255, 255), 5); //p1 is colored violet
        temp_string += "\nPoint 4: (" + p4.x + ", " + p4.y + ")";

        TextView temp_text = (TextView)findViewById(R.id.temp_text);
        temp_text.setText(temp_string+"\n Kare");
    }
    else if(temp_contour.toArray().length == 3)
    {
        System.out.println("Triangle");
        TextView temp_text = (TextView)findViewById(R.id.temp_text);
        temp_text.setText("\n Üçgen");
    }




    return new_image;
}

Quadrado:

Triângulo: