added empty() method to common features2d classes; fixed #831

modules/features2d/src/calonder.cpp

@@ -860,8 +860,11 @@ int RTreeClassifier::countNonZeroElements(float *vec, int n, double tol)
 void RTreeClassifier::read(const char* file_name)
 {
   std::ifstream file(file_name, std::ifstream::binary);
-  read(file);
-  file.close();
+  if( file.is_open() )
+  {
+      read(file);
+      file.close();
+  }
 }
 
 void RTreeClassifier::read(std::istream &is)

modules/features2d/src/descriptors.cpp

@@ -96,6 +96,11 @@ void DescriptorExtractor::read( const FileNode& )
 void DescriptorExtractor::write( FileStorage& ) const
 {}
 
+bool DescriptorExtractor::empty() const
+{
+    return false;
+}
+
 void DescriptorExtractor::removeBorderKeypoints( vector<KeyPoint>& keypoints,
                                                  Size imageSize, int borderSize )
 {
@@ -361,4 +366,9 @@ int OpponentColorDescriptorExtractor::descriptorType() const
     return descriptorExtractor->descriptorType();
 }
 
+bool OpponentColorDescriptorExtractor::empty() const
+{
+    return descriptorExtractor.empty() || (DescriptorExtractor*)(descriptorExtractor)->empty();
+}
+
 }

modules/features2d/src/detectors.cpp

@@ -96,6 +96,11 @@ void FeatureDetector::read( const FileNode& )
 void FeatureDetector::write( FileStorage& ) const
 {}
 
+bool FeatureDetector::empty() const
+{
+    return false;
+}
+
 Ptr<FeatureDetector> FeatureDetector::create( const string& detectorType )
 {
     FeatureDetector* fd = 0;
@@ -488,6 +493,11 @@ GridAdaptedFeatureDetector::GridAdaptedFeatureDetector( const Ptr<FeatureDetecto
     : detector(_detector), maxTotalKeypoints(_maxTotalKeypoints), gridRows(_gridRows), gridCols(_gridCols)
 {}
 
+bool GridAdaptedFeatureDetector::empty() const
+{
+    return detector.empty() || (FeatureDetector*)detector->empty();
+}
+
 struct ResponseComparator
 {
     bool operator() (const KeyPoint& a, const KeyPoint& b)
@@ -544,6 +554,11 @@ PyramidAdaptedFeatureDetector::PyramidAdaptedFeatureDetector( const Ptr<FeatureD
     : detector(_detector), levels(_levels)
 {}
 
+bool PyramidAdaptedFeatureDetector::empty() const
+{
+    return detector.empty() || (FeatureDetector*)detector->empty();
+}
+
 void PyramidAdaptedFeatureDetector::detectImpl( const Mat& image, vector<KeyPoint>& keypoints, const Mat& mask ) const
 {
     Mat src = image;

modules/features2d/src/matchers.cpp

@@ -213,7 +213,7 @@ void DescriptorMatcher::clear()
 
 bool DescriptorMatcher::empty() const
 {
-	return trainDescCollection.size() == 0;
+    return trainDescCollection.empty();
 }
 
 void DescriptorMatcher::train()
@@ -848,6 +848,11 @@ void GenericDescriptorMatcher::read( const FileNode& )
 void GenericDescriptorMatcher::write( FileStorage& ) const
 {}
 
+bool GenericDescriptorMatcher::empty() const
+{
+    return true;
+}
+
 /*
  * Factory function for GenericDescriptorMatch creating
  */
@@ -994,13 +999,18 @@ void OneWayDescriptorMatcher::write( FileStorage& fs ) const
     base->Write (fs);
 }
 
+bool OneWayDescriptorMatcher::empty() const
+{
+    return base.empty() || base->empty();
+}
+
 Ptr<GenericDescriptorMatcher> OneWayDescriptorMatcher::clone( bool emptyTrainData ) const
 {
     OneWayDescriptorMatcher* matcher = new OneWayDescriptorMatcher( params );
 
     if( !emptyTrainData )
     {
-        CV_Error( CV_StsNotImplemented, "deep clone dunctionality is not implemented, because "
+        CV_Error( CV_StsNotImplemented, "deep clone functionality is not implemented, because "
               "OneWayDescriptorBase has not copy constructor or clone method ");
 
         //matcher->base;
@@ -1175,6 +1185,11 @@ void FernDescriptorMatcher::write( FileStorage& fs ) const
 //    classifier->write(fs);
 }
 
+bool FernDescriptorMatcher::empty() const
+{
+    return classifier.empty() || classifier->empty();
+}
+
 Ptr<GenericDescriptorMatcher> FernDescriptorMatcher::clone( bool emptyTrainData ) const
 {
     FernDescriptorMatcher* matcher = new FernDescriptorMatcher( params );
@@ -1262,6 +1277,12 @@ void VectorDescriptorMatcher::write (FileStorage& fs) const
     extractor->write (fs);
 }
 
+bool VectorDescriptorMatcher::empty() const
+{
+    return extractor.empty() || extractor->empty() ||
+           matcher.empty() || matcher->empty();
+}
+
 Ptr<GenericDescriptorMatcher> VectorDescriptorMatcher::clone( bool emptyTrainData ) const
 {
     // TODO clone extractor

modules/features2d/src/planardetect.cpp

@@ -771,6 +771,10 @@ void FernClassifier::clear()
     vector<float>().swap(posteriors);
 }
 
+bool FernClassifier::empty() const
+{
+    return features.empty();
+}
 
 int FernClassifier::getLeaf(int fern, const Mat& _patch) const
 {