removed duplicated SIFT points (reported by Luca Del Tongo)

modules/features2d/src/sift.cpp

@@ -2130,6 +2130,70 @@ bool computeKeypointOrientations( VL::Sift& sift, const VL::Sift::Keypoint& keyp
     return false;
 }
 
+
+struct KeyPoint_LessThan
+{
+    KeyPoint_LessThan(const vector<KeyPoint>& _kp) : kp(&_kp) {}
+    bool operator()(int i, int j) const
+    {
+        const KeyPoint& kp1 = (*kp)[i];
+        const KeyPoint& kp2 = (*kp)[j];
+        if( kp1.pt.x != kp2.pt.x )
+            return kp1.pt.x < kp2.pt.x;
+        if( kp1.pt.y != kp2.pt.y )
+            return kp1.pt.y < kp2.pt.y;
+        if( kp1.size != kp2.size )
+            return kp1.size > kp2.size;
+        if( kp1.size != kp2.size )
+            return kp1.size > kp2.size;
+        if( kp1.angle != kp2.angle )
+            return kp1.angle < kp2.angle;
+        if( kp1.response != kp2.response )
+            return kp1.response > kp2.response;
+        if( kp1.octave != kp2.octave )
+            return kp1.octave > kp2.octave;
+        if( kp1.class_id != kp2.class_id )
+            return kp1.class_id > kp2.class_id;
+        
+        return i < j;
+    }
+    const vector<KeyPoint>* kp;
+};
+
+
+static void removeDuplicatedKeypoints(vector<KeyPoint>& keypoints)
+{
+    int i, j, n = (int)keypoints.size();
+    vector<int> kpidx(n);
+    vector<uchar> mask(n, (uchar)1);
+    
+    for( i = 0; i < n; i++ )
+        kpidx[i] = i;
+    std::sort(kpidx.begin(), kpidx.end(), KeyPoint_LessThan(keypoints));
+    for( i = 1, j = 0; i < n; i++ )
+    {
+        KeyPoint& kp1 = keypoints[kpidx[i]];
+        KeyPoint& kp2 = keypoints[kpidx[j]];
+        if( kp1.pt.x != kp2.pt.x || kp1.pt.y != kp2.pt.y ||
+            kp1.size != kp2.size || kp1.angle != kp2.angle )
+            j = i;
+        else
+            mask[kpidx[i]] = 0;
+    }
+
+    for( i = j = 0; i < n; i++ )
+    {
+        if( mask[i] )
+        {
+            if( i != j )
+                keypoints[j] = keypoints[i];
+            j++;
+        }
+    }
+    keypoints.resize(j);
+}
+
+
 // detectors
 void SIFT::operator()(const Mat& img, const Mat& mask,
                       vector<KeyPoint>& keypoints) const
@@ -2160,6 +2224,7 @@ void SIFT::operator()(const Mat& img, const Mat& mask,
             keypoints.push_back( vlKeypointToOcv(vlsift, *iter, angleVal*a_180divPI) );
         }
     }
+    removeDuplicatedKeypoints(keypoints);
 }
 
 struct InvalidKeypoint