Add nnSymmetryTest. No gtest yet

src/matchers/matcher_base.cpp

@@ -308,6 +308,32 @@ void MatcherBase::ransacTest(const KeyPointVector& _raw_kps1,
     }
 }
 
+void MatcherBase::nnSymmetryTest(const std::vector<DMatchVector>& _matches1,
+                                 const std::vector<DMatchVector>& _matches2,
+                                 DMatchVector& _sym_matches)
+{
+    // for all matches image 1 -> image 2
+    for (std::vector<DMatchVector>::const_iterator itM1 = _matches1.begin(); itM1 != _matches1.end(); ++itM1)
+    {
+        if (itM1->size() < 2) // ignore deleted matches
+            continue;
+
+        // for all matches image 2 -> image 1
+        for (std::vector<DMatchVector>::const_iterator itM2 = _matches2.begin(); itM2 != _matches2.end(); ++itM2)
+        {
+            if (itM2->size() < 2) // ignore deleted matches
+                continue;
+
+            // Match symmetry test
+            if ((*itM1)[0].queryIdx == (*itM2)[0].trainIdx && (*itM2)[0].queryIdx == (*itM1)[0].trainIdx)
+            {
+                // add symmetrical match
+                _sym_matches.push_back(cv::DMatch((*itM1)[0].queryIdx, (*itM1)[0].trainIdx, (*itM1)[0].distance));
+                break; // next match in image 1 -> image 2
+            }
+        }
+    }
+}
 
 cv::Mat MatcherBase::drawMatches(const cv::Mat _img1, const cv::Mat _img2, KeyPointVector _kpts12_img1, KeyPointVector _kpts12_img2)
 {

src/matchers/matcher_base.h

@@ -134,6 +134,11 @@ class MatcherBase : public VUBase, public std::enable_shared_from_this<MatcherBa
                         KeyPointVector& _inlier_kps2,
                         DMatchVector& _inlier_matches);
 
+        // Check symmetry between nn matches from <im1->im2> and from <im2->im1> pairs
+        void nnSymmetryTest(const std::vector<DMatchVector>& _matches1,
+                            const std::vector<DMatchVector>& _matches2,
+                            DMatchVector& _sym_matches);
+
         // Factory method
         static MatcherBasePtr create(const std::string& _unique_name,
                                      const ParamsBasePtr _params);