视觉SLAM--回环检测

文章目录

创建字典
相似度计算
增加字典规模

回环检测的意义：可以使 后端位姿图得到一个 全局一致估计。
视觉SLAM的主流做法： 基于外观的回环检测方法，仅 根据两幅图像的相似性确定回环检测关系。这种方法，摆脱了累计误差，使得回环检测模块可以称为SLAM系统中相对独立的模块。

创建字典

词袋，Bag-of-Words(BoW),目的是用"图像上有哪几种特征"来描述一幅图像。

ch11\feature_training.cpp

int main( int argc, char** argv ) {// read the image 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) );}// detect ORB featurescout<<"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 );}// create vocabulary cout<<"creating vocabulary ... "<<endl;DBoW3::Vocabulary vocab;vocab.create( descriptors );cout<<"vocabulary info: "<<vocab<<endl;vocab.save( "vocabulary.yml.gz" );cout<<"done"<<endl;return 0;
}

相似度计算

ch11\loop_closure.cpp

int main(int argc, char **argv) {// read the images and database  cout << "reading database" << endl;DBoW3::Vocabulary vocab("./vocabulary.yml.gz");// DBoW3::Vocabulary vocab("./vocab_larger.yml.gz");  // use large vocab if you want: 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 lead to overfit.// detect ORB featurescout << "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=4cout << "searching for image " << i << " returns " << ret << endl << endl;}cout << "done." << endl;
}

增加字典规模

ch11\gen_vocab_large.cpp

int main( int argc, char** argv )
{string dataset_dir = argv[1];ifstream fin ( dataset_dir+"/associate.txt" );if ( !fin ){cout<<"please generate the associate file called associate.txt!"<<endl;return 1;}vector<string> rgb_files, depth_files;vector<double> rgb_times, depth_times;while ( !fin.eof() ){string rgb_time, rgb_file, depth_time, depth_file;fin>>rgb_time>>rgb_file>>depth_time>>depth_file;rgb_times.push_back ( atof ( rgb_time.c_str() ) );depth_times.push_back ( atof ( depth_time.c_str() ) );rgb_files.push_back ( dataset_dir+"/"+rgb_file );depth_files.push_back ( dataset_dir+"/"+depth_file );if ( fin.good() == false )break;}fin.close();cout<<"generating features ... "<<endl;vector<Mat> descriptors;Ptr< Feature2D > detector = ORB::create();int index = 1;for ( string rgb_file:rgb_files ){Mat image = imread(rgb_file);vector<KeyPoint> keypoints; Mat descriptor;detector->detectAndCompute( image, Mat(), keypoints, descriptor );descriptors.push_back( descriptor );cout<<"extracting features from image " << index++ <<endl;}cout<<"extract total "<<descriptors.size()*500<<" features."<<endl;// create vocabulary cout<<"creating vocabulary, please wait ... "<<endl;DBoW3::Vocabulary vocab;vocab.create( descriptors );cout<<"vocabulary info: "<<vocab<<endl;vocab.save( "vocab_larger.yml.gz" );cout<<"done"<<endl;return 0;
}