DescriptorExtractor: added defaultNorm() to return default norm type.

Added the defaultNorm() method to the DescriptorExtractor class. This method returns the default norm type for each descriptor type. The tests and C/C++ samples were updated to get the norm type directly from the DescriptorExtractor inherited classes.

This was reported in feature report #2182 (http://code.opencv.org/issues/2182). It will make it possible to get the norm type usually applied matching method for each descriptor, instead of passing it manually.

modules/features2d/src/brief.cpp

@@ -125,6 +125,11 @@ int BriefDescriptorExtractor::descriptorType() const
     return CV_8UC1;
 }
 
+int BriefDescriptorExtractor::defaultNorm() const
+{
+    return NORM_HAMMING;
+}
+
 void BriefDescriptorExtractor::read( const FileNode& fn)
 {
     int dSize = fn["descriptorSize"];

modules/features2d/src/brisk.cpp

@@ -712,6 +712,12 @@ BRISK::descriptorType() const
   return CV_8U;
 }
 
+int
+BRISK::defaultNorm() const
+{
+  return NORM_HAMMING;
+}
+
 BRISK::~BRISK()
 {
   delete[] patternPoints_;

modules/features2d/src/descriptors.cpp

@@ -247,6 +247,11 @@ int OpponentColorDescriptorExtractor::descriptorType() const
     return descriptorExtractor->descriptorType();
 }
 
+int OpponentColorDescriptorExtractor::defaultNorm() const
+{
+    return descriptorExtractor->defaultNorm();
+}
+
 bool OpponentColorDescriptorExtractor::empty() const
 {
     return !descriptorExtractor || descriptorExtractor->empty();

modules/features2d/src/freak.cpp

@@ -623,4 +623,9 @@ int FREAK::descriptorType() const {
     return CV_8U;
 }
 
+int FREAK::defaultNorm() const
+{
+    return NORM_HAMMING;
+}
+
 } // END NAMESPACE CV

modules/features2d/src/orb.cpp

@@ -575,6 +575,11 @@ int ORB::descriptorType() const
     return CV_8U;
 }
 
+int ORB::defaultNorm() const
+{
+    return NORM_HAMMING;
+}
+
 /** Compute the ORB features and descriptors on an image
  * @param img the image to compute the features and descriptors on
  * @param mask the mask to apply