Square Detection Algorithm

  Mat clonedMat = imgSource.clone();

            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();
            List<MatOfPoint> largest_contours = new ArrayList<MatOfPoint>();
            MatOfPoint2f maxCurve = new MatOfPoint2f();

            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);
                        MatOfPoint points = new MatOfPoint( approxCurve.toArray() );
                        Rect rect = Imgproc.boundingRect(points);

                        if(isDebug)
                        {
                            Imgproc.drawContours(clonedMat, contours, idx, new Scalar(0,0,255), 5);
                        }

                    }
                }
            }

            String temp_string = null;

            try
            {
                //BGR
                point1 = maxCurve.get(1, 0);
                p1 = new org.opencv.core.Point(point1[0]+30, point1[1]+30);
                //Imgproc.circle(clonedMat, p1, 20, new Scalar(255, 0, 0), 5); //blue
                temp_string = "Point 1: (" + p1.x + ", " + p1.y + ")";

                point2 = maxCurve.get(0, 0);
                p2 = new org.opencv.core.Point(point2[0]-30, point2[1]+30);
                //Imgproc.circle(clonedMat, p2, 20, new Scalar(0, 255, 0), 5);//green
                temp_string += "\nPoint 2: (" + p2.x + ", " + p2.y + ")";

                point3 = maxCurve.get(3, 0);
                p3 = new org.opencv.core.Point(point3[0]-50, point3[1]-50);
                //Imgproc.circle(clonedMat, p3, 20, new Scalar(0, 0, 255), 5);//red
                temp_string += "\nPoint 3: (" + p3.x + ", " + p3.y + ")";

                point4 = maxCurve.get(2, 0);
                p4 = new org.opencv.core.Point(point4[0]+50, point4[1]-50);
                //Imgproc.circle(clonedMat, p4, 20, new Scalar(0, 255, 255), 5); // yellow
                temp_string += "\nPoint 4: (" + p4.x + ", " + p4.y + ")";
            }catch (NullPointerException e)
            {
                this.cancel(true);
            }