/// <summary>
/// Recover the homography matrix using RANDSAC. If the matrix cannot be recovered, null is returned.
/// </summary>
/// <param name="matchedFeatures">The Matched Features, only the first ModelFeature will be considered</param>
/// <returns>The homography matrix, if it cannot be found, null is returned</returns>
public static HomographyMatrix GetHomographyMatrixFromMatchedFeatures(MatchedSURFFeature[] matchedFeatures)
{
if (matchedFeatures.Length < 4)
return null;
HomographyMatrix homography;
if (matchedFeatures.Length < _randsacRequiredMatch)
{ // Too few points for randsac, use 4 points only
PointF[] pts1 = new PointF[4];
PointF[] pts2 = new PointF[4];
for (int i = 0; i < 4; i++)
{
pts1[i] = matchedFeatures[i].SimilarFeatures[0].Feature.Point.pt;
pts2[i] = matchedFeatures[i].ObservedFeature.Point.pt;
}
homography = CameraCalibration.GetPerspectiveTransform(pts1, pts2);
}
else
{
//use randsac to find the Homography Matrix
PointF[] pts1 = new PointF[matchedFeatures.Length];
PointF[] pts2 = new PointF[matchedFeatures.Length];
for (int i = 0; i < matchedFeatures.Length; i++)
{
pts1[i] = matchedFeatures[i].SimilarFeatures[0].Feature.Point.pt;
pts2[i] = matchedFeatures[i].ObservedFeature.Point.pt;
}
homography = CameraCalibration.FindHomography(
pts1, //points on the model image
pts2, //points on the observed image
CvEnum.HOMOGRAPHY_METHOD.RANSAC,
3);
if (homography == null)
return null;
}
if (homography.IsValid(10))
return homography;
else
{
homography.Dispose();
return null;
}
}
/*
* private static int CompareSimilarFeature(SimilarFeature f1, SimilarFeature f2)
* {
* if (f1.Distance < f2.Distance)
* return -1;
* if (f1.Distance == f2.Distance)
* return 0;
* else
* return 1;
* }*/
/// <summary>
/// Match the SURF feature from the observed image to the features from the model image
/// </summary>
/// <param name="observedFeatures">The SURF feature from the observed image</param>
/// <param name="k">The number of neighbors to find</param>
/// <param name="emax">For k-d tree only: the maximum number of leaves to visit.</param>
/// <returns>The matched features</returns>
public MatchedSURFFeature[] MatchFeature(SURFFeature[] observedFeatures, int k, int emax)
{
if (observedFeatures.Length == 0)
{
return(new MatchedSURFFeature[0]);
}
float[][] descriptors = new float[observedFeatures.Length][];
for (int i = 0; i < observedFeatures.Length; i++)
{
descriptors[i] = observedFeatures[i].Descriptor;
}
using (Matrix <int> result1 = new Matrix <int>(descriptors.Length, k))
using (Matrix <float> dist1 = new Matrix <float>(descriptors.Length, k))
{
_modelIndex.KnnSearch(Util.GetMatrixFromDescriptors(descriptors), result1, dist1, k, emax);
int[,] indexes = result1.Data;
float[,] distances = dist1.Data;
MatchedSURFFeature[] res = new MatchedSURFFeature[observedFeatures.Length];
List <SimilarFeature> matchedFeatures = new List <SimilarFeature>();
for (int i = 0; i < res.Length; i++)
{
matchedFeatures.Clear();
for (int j = 0; j < k; j++)
{
int index = indexes[i, j];
if (index >= 0)
{
matchedFeatures.Add(new SimilarFeature(distances[i, j], _modelFeatures[index]));
}
}
res[i].ObservedFeature = observedFeatures[i];
res[i].SimilarFeatures = matchedFeatures.ToArray();
}
return(res);
}
}
/// <summary>
/// Eliminate the matched features whose scale and rotation do not aggree with the majority's scale and rotation.
/// </summary>
/// <param name="rotationBins">The numbers of bins for rotation, a good value might be 20 (which means each bin covers 18 degree)</param>
/// <param name="scaleIncrement">This determins the different in scale for neighbour hood bins, a good value might be 1.5 (which means matched features in bin i+1 is scaled 1.5 times larger than matched features in bin i</param>
/// <param name="matchedFeatures">The matched feature that will be participated in the voting. For each matchedFeatures, only the zero indexed ModelFeature will be considered.</param>
public static MatchedSURFFeature[] VoteForSizeAndOrientation(MatchedSURFFeature[] matchedFeatures, double scaleIncrement, int rotationBins)
{
int elementsCount = matchedFeatures.Length;
float[] scales = new float[elementsCount];
float[] rotations = new float[elementsCount];
float[] flags = new float[elementsCount];
float minScale = float.MaxValue;
float maxScale = float.MinValue;
for (int i = 0; i < matchedFeatures.Length; i++)
{
float scale = (float)matchedFeatures[i].ObservedFeature.Point.size / (float)matchedFeatures[i].SimilarFeatures[0].Feature.Point.size;
scale = (float)Math.Log10(scale);
scales[i] = scale;
if (scale < minScale)
{
minScale = scale;
}
if (scale > maxScale)
{
maxScale = scale;
}
float rotation = matchedFeatures[i].ObservedFeature.Point.dir - matchedFeatures[i].SimilarFeatures[0].Feature.Point.dir;
rotations[i] = rotation < 0.0 ? rotation + 360 : rotation;
}
int scaleBinSize = (int)Math.Max(((maxScale - minScale) / Math.Log10(scaleIncrement)), 1);
int count;
using (DenseHistogram h = new DenseHistogram(new int[] { scaleBinSize, rotationBins }, new RangeF[] { new RangeF(minScale, maxScale), new RangeF(0, 360) }))
{
GCHandle scaleHandle = GCHandle.Alloc(scales, GCHandleType.Pinned);
GCHandle rotationHandle = GCHandle.Alloc(rotations, GCHandleType.Pinned);
GCHandle flagsHandle = GCHandle.Alloc(flags, GCHandleType.Pinned);
using (Matrix <float> flagsMat = new Matrix <float>(1, elementsCount, flagsHandle.AddrOfPinnedObject()))
using (Matrix <float> scalesMat = new Matrix <float>(1, elementsCount, scaleHandle.AddrOfPinnedObject()))
using (Matrix <float> rotationsMat = new Matrix <float>(1, elementsCount, rotationHandle.AddrOfPinnedObject()))
{
h.Calculate(new Matrix <float>[] { scalesMat, rotationsMat }, true, null);
float minVal, maxVal;
int[] minLoc, maxLoc;
h.MinMax(out minVal, out maxVal, out minLoc, out maxLoc);
h.Threshold(maxVal * 0.5);
CvInvoke.cvCalcBackProject(new IntPtr[] { scalesMat.Ptr, rotationsMat.Ptr }, flagsMat.Ptr, h.Ptr);
count = CvInvoke.cvCountNonZero(flagsMat);
}
scaleHandle.Free();
rotationHandle.Free();
flagsHandle.Free();
MatchedSURFFeature[] matchedGoodFeatures = new MatchedSURFFeature[count];
int index = 0;
for (int i = 0; i < matchedFeatures.Length; i++)
{
if (flags[i] != 0)
{
matchedGoodFeatures[index++] = matchedFeatures[i];
}
}
return(matchedGoodFeatures);
}
}
/*
private static int CompareSimilarFeature(SimilarFeature f1, SimilarFeature f2)
{
if (f1.Distance < f2.Distance)
return -1;
if (f1.Distance == f2.Distance)
return 0;
else
return 1;
}*/
/// <summary>
/// Match the SURF feature from the observed image to the features from the model image
/// </summary>
/// <param name="observedFeatures">The SURF feature from the observed image</param>
/// <param name="k">The number of neighbors to find</param>
/// <param name="emax">For k-d tree only: the maximum number of leaves to visit.</param>
/// <returns>The matched features</returns>
public MatchedSURFFeature[] MatchFeature(SURFFeature[] observedFeatures, int k, int emax)
{
if (observedFeatures.Length == 0) return new MatchedSURFFeature[0];
float[][] descriptors = new float[observedFeatures.Length][];
for (int i = 0; i < observedFeatures.Length; i++)
descriptors[i] = observedFeatures[i].Descriptor;
using(Matrix<int> result1 = new Matrix<int>(descriptors.Length, k))
using (Matrix<float> dist1 = new Matrix<float>(descriptors.Length, k))
{
_modelIndex.KnnSearch(Util.GetMatrixFromDescriptors(descriptors), result1, dist1, k, emax);
int[,] indexes = result1.Data;
float[,] distances = dist1.Data;
MatchedSURFFeature[] res = new MatchedSURFFeature[observedFeatures.Length];
List<SimilarFeature> matchedFeatures = new List<SimilarFeature>();
for (int i = 0; i < res.Length; i++)
{
matchedFeatures.Clear();
for (int j = 0; j < k; j++)
{
int index = indexes[i, j];
if (index >= 0)
{
matchedFeatures.Add(new SimilarFeature(distances[i, j], _modelFeatures[index]));
}
}
res[i].ObservedFeature = observedFeatures[i];
res[i].SimilarFeatures = matchedFeatures.ToArray();
}
return res;
}
}
/// <summary>
/// Eliminate the matched features whose scale and rotation do not aggree with the majority's scale and rotation.
/// </summary>
/// <param name="rotationBins">The numbers of bins for rotation, a good value might be 20 (which means each bin covers 18 degree)</param>
/// <param name="scaleIncrement">This determins the different in scale for neighbour hood bins, a good value might be 1.5 (which means matched features in bin i+1 is scaled 1.5 times larger than matched features in bin i</param>
/// <param name="matchedFeatures">The matched feature that will be participated in the voting. For each matchedFeatures, only the zero indexed ModelFeature will be considered.</param>
public static MatchedSURFFeature[] VoteForSizeAndOrientation(MatchedSURFFeature[] matchedFeatures, double scaleIncrement, int rotationBins)
{
int elementsCount = matchedFeatures.Length;
float[] scales = new float[elementsCount];
float[] rotations = new float[elementsCount];
float[] flags = new float[elementsCount];
float minScale = float.MaxValue;
float maxScale = float.MinValue;
for (int i = 0; i < matchedFeatures.Length; i++)
{
float scale = (float)matchedFeatures[i].ObservedFeature.Point.size / (float)matchedFeatures[i].SimilarFeatures[0].Feature.Point.size;
scale = (float)Math.Log10(scale);
scales[i] = scale;
if (scale < minScale) minScale = scale;
if (scale > maxScale) maxScale = scale;
float rotation = matchedFeatures[i].ObservedFeature.Point.dir - matchedFeatures[i].SimilarFeatures[0].Feature.Point.dir;
rotations[i] = rotation < 0.0 ? rotation + 360 : rotation;
}
int scaleBinSize = (int)Math.Max(((maxScale - minScale) / Math.Log10(scaleIncrement)), 1);
int count;
using (DenseHistogram h = new DenseHistogram(new int[] { scaleBinSize, rotationBins }, new RangeF[] { new RangeF(minScale, maxScale), new RangeF(0, 360) }))
{
GCHandle scaleHandle = GCHandle.Alloc(scales, GCHandleType.Pinned);
GCHandle rotationHandle = GCHandle.Alloc(rotations, GCHandleType.Pinned);
GCHandle flagsHandle = GCHandle.Alloc(flags, GCHandleType.Pinned);
using (Matrix<float> flagsMat = new Matrix<float>(1, elementsCount, flagsHandle.AddrOfPinnedObject()))
using (Matrix<float> scalesMat = new Matrix<float>(1, elementsCount, scaleHandle.AddrOfPinnedObject()))
using (Matrix<float> rotationsMat = new Matrix<float>(1, elementsCount, rotationHandle.AddrOfPinnedObject()))
{
h.Calculate(new Matrix<float>[] { scalesMat, rotationsMat }, true, null);
float minVal, maxVal;
int[] minLoc, maxLoc;
h.MinMax(out minVal, out maxVal, out minLoc, out maxLoc);
h.Threshold(maxVal * 0.5);
CvInvoke.cvCalcBackProject(new IntPtr[] { scalesMat.Ptr, rotationsMat.Ptr }, flagsMat.Ptr, h.Ptr);
count = CvInvoke.cvCountNonZero(flagsMat);
}
scaleHandle.Free();
rotationHandle.Free();
flagsHandle.Free();
MatchedSURFFeature[] matchedGoodFeatures = new MatchedSURFFeature[count];
int index = 0;
for (int i = 0; i < matchedFeatures.Length; i++)
if (flags[i] != 0)
matchedGoodFeatures[index++] = matchedFeatures[i];
return matchedGoodFeatures;
}
}
/// <summary>
/// Filter the matched Features, such that if a match is not unique, it is rejected.
/// </summary>
/// <param name="matchedFeatures">The Matched SURF features, each of them has the model feature sorted by distance. (e.g. SortMatchedFeaturesByDistance )</param>
/// <param name="uniquenessThreshold">The distance different ratio which a match is consider unique, a good number will be 0.8</param>
/// <returns>The filtered matched SURF Features</returns>
public static MatchedSURFFeature[] VoteForUniqueness(MatchedSURFFeature[] matchedFeatures, double uniquenessThreshold)
{
return Array.FindAll<MatchedSURFFeature>(matchedFeatures,
delegate(MatchedSURFFeature f)
{
return
f.SimilarFeatures.Length == 1 //this is the only match
|| (f.SimilarFeatures[0].Distance / f.SimilarFeatures[1].Distance <= uniquenessThreshold); //if the first model feature is a good match
});
}