SURF 特征法

 public static void FindMatch(Mat modelImage, Mat observedImage, out long matchTime, out VectorOfKeyPoint modelKeyPoints, out VectorOfKeyPoint observedKeyPoints, VectorOfVectorOfDMatch matches, out Mat mask, out Mat homography)
        {
            int k = 2;
            double uniquenessThreshold = 0.8;
            double hessianThresh = 300;

            Stopwatch watch;
            homography = null;

            modelKeyPoints = new VectorOfKeyPoint();
            observedKeyPoints = new VectorOfKeyPoint();
            using (UMat uModelImage = modelImage.ToUMat(AccessType.Read))
            using (UMat uObservedImage = observedImage.ToUMat(AccessType.Read))
            {
                SURF surfCPU = new SURF(hessianThresh);
                //extract features from the object image
                UMat modelDescriptors = new UMat();
                surfCPU.DetectAndCompute(uModelImage, null, modelKeyPoints, modelDescriptors, false);
                
                watch = Stopwatch.StartNew();

                // extract features from the observed image
                UMat observedDescriptors = new UMat();
                surfCPU.DetectAndCompute(uObservedImage, null, observedKeyPoints, observedDescriptors, false);
                BFMatcher matcher = new BFMatcher(DistanceType.L2);
                matcher.Add(modelDescriptors);

                matcher.KnnMatch(observedDescriptors, matches, k, null);
                mask = new Mat(matches.Size, 1, DepthType.Cv8U, 1);
                mask.SetTo(new MCvScalar(255));
                Features2DToolbox.VoteForUniqueness(matches, uniquenessThreshold, mask);

                int nonZeroCount = CvInvoke.CountNonZero(mask);
                if (nonZeroCount >= 4)
                {
                    nonZeroCount = Features2DToolbox.VoteForSizeAndOrientation(modelKeyPoints, observedKeyPoints,
                       matches, mask, 1.5, 20);
                    if (nonZeroCount >= 4)
                        homography = Features2DToolbox.GetHomographyMatrixFromMatchedFeatures(modelKeyPoints,
                           observedKeyPoints, matches, mask, 2);
                }

                watch.Stop();

            }
            matchTime = watch.ElapsedMilliseconds;
        }

        /// <summary>
        /// Draw the model image and observed image, the matched features and homography projection.
        /// </summary>
        /// <param name="modelImage">The model image</param>
        /// <param name="observedImage">The observed image</param>
        /// <param name="matchTime">The output total time for computing the homography matrix.</param>
        /// <returns>The model image and observed image, the matched features and homography projection.</returns>
        public static Mat Draw(Mat modelImage, Mat observedImage, out long matchTime)
        {
            Mat homography;
            VectorOfKeyPoint modelKeyPoints;
            VectorOfKeyPoint observedKeyPoints;
            using (VectorOfVectorOfDMatch matches = new VectorOfVectorOfDMatch())
            {
                Mat mask;
                FindMatch(modelImage, observedImage, out matchTime, out modelKeyPoints, out observedKeyPoints, matches,
                   out mask, out homography);

                //Draw the matched keypoints
                Mat result = new Mat();
                Features2DToolbox.DrawMatches(modelImage, modelKeyPoints, observedImage, observedKeyPoints,
                   matches, result, new MCvScalar(255, 255, 255), new MCvScalar(255, 255, 255), mask);

                #region draw the projected region on the image

                if (homography != null)
                {
                    //draw a rectangle along the projected model
                    Rectangle rect = new Rectangle(Point.Empty, modelImage.Size);
                    PointF[] pts = new PointF[]
                    {
                  new PointF(rect.Left, rect.Bottom),
                  new PointF(rect.Right, rect.Bottom),
                  new PointF(rect.Right, rect.Top),
                  new PointF(rect.Left, rect.Top)
                    };
                    pts = CvInvoke.PerspectiveTransform(pts, homography);

                    Point[] points = Array.ConvertAll<PointF, Point>(pts, Point.Round);
                    using (VectorOfPoint vp = new VectorOfPoint(points))
                    {
                        CvInvoke.Polylines(result, vp, true, new MCvScalar(255, 0, 0, 255), 5);
                    }

                }

                #endregion

                return result;

            }
        }