How to filter OpenSURF invalid matches using RANSAC in C#

Question

I have the code (OpenSURF C#, IPoint struct used), it calculates SURF matches for two images:

var surfEngine = new EngineSURF();

points[0] = surfEngine.GetPoints(images[0]).ToList();
points[1] = surfEngine.GetPoints(images[1]).ToList();
points[2] = surfEngine.GetPoints(images[2]).ToList();
points[3] = surfEngine.GetPoints(images[3]).ToList();

var match1 = surfEngine.GetMatches(points[0], points[1]).ToArray();
var match2 = surfEngine.GetMatches(points[0], points[2]).ToArray();
var match3 = surfEngine.GetMatches(points[0], points[3]).ToArray();

outBmps[0] = surfEngine.PaintSURF(new Bitmap(images[0]), new Bitmap(images[1]), match1);
outBmps[1] = surfEngine.PaintSURF(new Bitmap(images[0]), new Bitmap(images[2]), match2);
outBmps[2] = surfEngine.PaintSURF(new Bitmap(images[0]), new Bitmap(images[3]), match3);

var path = Path.GetDirectoryName(images[0]) ?? string.Empty;

Checks.StringIsNotNull(path);

if(outBmps[0] != null) outBmps[0].Save(Path.Combine(path,"result0_1.png"), ImageFormat.Png);
if (outBmps[1] != null) outBmps[1].Save(Path.Combine(path, "result0_2.png"), ImageFormat.Png);
if (outBmps[2] != null) outBmps[2].Save(Path.Combine(path, "result0_3.png"), ImageFormat.Png);

And I have next matches:

1) Best matches

2) Wrong matches

3) Wrong matches

How I can filter wrong (2, 3) matches with RANSAC? Have any sample code? Thanks!

Answer 1

Accord.Imaging allows find SURF features and estimate points using RANSAC.

var correlationPoints1 = matches[0];
var correlationPoints2 = matches[1];
var ransac = new RansacHomographyEstimator(0.10, 0.99);
var homography = ransac.Estimate(correlationPoints1, correlationPoints2);
var inliers1 = correlationPoints1.Submatrix(ransac.Inliers);
var inliers2 = correlationPoints2.Submatrix(ransac.Inliers);
var result = new IntPoint[][]
                    {
                        inliers1,
                        inliers2
                    };

http://www.nuget.org/packages/Accord.Imaging/

http://accord-framework.net/samples.html