loop closing

ch9/CMakeLists.txt

@@ -16,3 +16,5 @@ set( DBoW3_LIBS "/usr/local/lib/libDBoW3.a" )
 add_executable( feature_training feature_training.cpp )
 target_link_libraries( feature_training ${OpenCV_LIBS} ${DBoW3_LIBS} )
 
+add_executable( loop_closure loop_closure.cpp )
+target_link_libraries( loop_closure ${OpenCV_LIBS} ${DBoW3_LIBS} )

ch9/loop_closure.cpp

@@ -0,0 +1,73 @@
+#include "DBoW3/DBoW3.h"
+#include <opencv2/core/core.hpp>
+#include <opencv2/highgui/highgui.hpp>
+#include <opencv2/features2d/features2d.hpp>
+#include <iostream>
+#include <vector>
+#include <string>
+
+using namespace cv;
+using namespace std;
+
+int main( int argc, char** argv )
+{
+    // read the images and database  
+    cout<<"reading database"<<endl;
+    DBoW3::Vocabulary vocab("./vocabulary.yml.gz");
+    if ( vocab.empty() )
+    {
+        cerr<<"Vocabulary does not exist."<<endl;
+        return 1;
+    }
+    cout<<"reading images... "<<endl;
+    vector<Mat> images; 
+    for ( int i=0; i<10; i++ )
+    {
+        string path = "./data/"+to_string(i+1)+".png";
+        images.push_back( imread(path) );
+    }
+
+    // NOTE: in this case we are comparing images with a vocabulary generated by themselves, this may leed to overfitting.  
+    // detect ORB features
+    cout<<"detecting ORB features ... "<<endl;
+    Ptr< Feature2D > detector = ORB::create();
+    vector<Mat> descriptors;
+    for ( Mat& image:images )
+    {
+        vector<KeyPoint> keypoints; 
+        Mat descriptor;
+        detector->detectAndCompute( image, Mat(), keypoints, descriptor );
+        descriptors.push_back( descriptor );
+    }
+
+    // we can compare the images directly or we can compare one image to a database 
+    // images 
+    cout<<"comparing images with images "<<endl;
+    for ( int i=0; i<images.size(); i++ )
+    {
+        DBoW3::BowVector v1;
+        vocab.transform( descriptors[i], v1 );
+        for ( int j=i; j<images.size(); j++ )
+        {
+            DBoW3::BowVector v2;
+            vocab.transform( descriptors[j], v2 );
+            double score = vocab.score(v1, v2);
+            cout<<"image "<<i<<" vs image "<<j<<" : "<<score<<endl;
+        }
+        cout<<endl;
+    }
+
+    // or with database 
+    cout<<"comparing images with database "<<endl;
+    DBoW3::Database db( vocab, false, 0);
+    for ( int i=0; i<descriptors.size(); i++ )
+        db.add(descriptors[i]);
+    cout<<"database info: "<<db<<endl;
+    for ( int i=0; i<descriptors.size(); i++ )
+    {
+        DBoW3::QueryResults ret;
+        db.query( descriptors[i], ret, 4);      // max result=4
+        cout<<"searching for image "<<i<<" returns "<<ret<<endl<<endl;
+    }
+    cout<<"done."<<endl;
+}