ORB_SLAM2源码解析－框架

看了很多SLAM的源码阅读和解析了，有的人已经写了很好了，但是对于一个刚入门的菜鸟来说还是看不太懂，没办法具体到每一个函数的功能，虽然大体的框架知道是怎么回事，但是细细想有搞不明白，所以决定自己写一个博客来详细记录学习的过程，重要的是做笔记，要不然总是忘记。

首先从框架说起，下面的代码来自ORB_SLAM2中的mono_kitti.cc

#include<iostream>
#include<algorithm>
#include<fstream>
#include<chrono>
#include<iomanip>

#include<opencv2/core/core.hpp>

#include"System.h"

using namespace std;

void LoadImages(const string &strSequence, vector<string> &vstrImageFilenames,
                vector<double> &vTimestamps);

int main(int argc, char **argv)
{
    if(argc != 4)
    {
        cerr << endl << "Usage: ./mono_kitti path_to_vocabulary path_to_settings path_to_sequence" << endl;
        return 1;
    }

    // Retrieve paths to images
    //检索图片位置
    vector<string> vstrImageFilenames;
    vector<double> vTimestamps;
    LoadImages(string(argv[3]), vstrImageFilenames, vTimestamps);

    int nImages = vstrImageFilenames.size();

    // Create SLAM system. It initializes all system threads and gets ready to process frames.
    ORB_SLAM2::System SLAM(argv[1],argv[2],ORB_SLAM2::System::MONOCULAR,true);

    // Vector for tracking time statistics
    vector<float> vTimesTrack;
    vTimesTrack.resize(nImages);

    cout << endl << "-------" << endl;
    cout << "Start processing sequence ..." << endl;
    cout << "Images in the sequence: " << nImages << endl << endl;

    // Main loop
    cv::Mat im;
    for(int ni=0; ni<nImages; ni++)
    {
        // Read image from file
        im = cv::imread(vstrImageFilenames[ni],CV_LOAD_IMAGE_UNCHANGED);
        double tframe = vTimestamps[ni];

        if(im.empty())
        {
            cerr << endl << "Failed to load image at: " << vstrImageFilenames[ni] << endl;
            return 1;
        }

//计时
#ifdef COMPILEDWITHC11
        std::chrono::steady_clock::time_point t1 = std::chrono::steady_clock::now();
#else
        std::chrono::monotonic_clock::time_point t1 = std::chrono::monotonic_clock::now();
#endif

        // Pass the image to the SLAM system
        //将图片和时间戳写入系统
        SLAM.TrackMonocular(im,tframe);

#ifdef COMPILEDWITHC11
        std::chrono::steady_clock::time_point t2 = std::chrono::steady_clock::now();
#else
        std::chrono::monotonic_clock::time_point t2 = std::chrono::monotonic_clock::now();
#endif

        double ttrack= std::chrono::duration_cast<std::chrono::duration<double> >(t2 - t1).count();

        vTimesTrack[ni]=ttrack;

        // Wait to load the next frame
        double T=0;
        if(ni<nImages-1)
            T = vTimestamps[ni+1]-tframe;
        else if(ni>0)
            T = tframe-vTimestamps[ni-1];

        if(ttrack<T)
            usleep((T-ttrack)*1e6);
    }

    // Stop all threads
    SLAM.Shutdown();

    // Tracking time statistics
    sort(vTimesTrack.begin(),vTimesTrack.end());
    float totaltime = 0;
    for(int ni=0; ni<nImages; ni++)
    {
        totaltime+=vTimesTrack[ni];
    }
    cout << "-------" << endl << endl;
    cout << "median tracking time: " << vTimesTrack[nImages/2] << endl;
    cout << "mean tracking time: " << totaltime/nImages << endl;

    // Save camera trajectory
    //保存相机轨迹
    SLAM.SaveKeyFrameTrajectoryTUM("KeyFrameTrajectory.txt");    

    return 0;
}

void LoadImages(const string &strPathToSequence, vector<string> &vstrImageFilenames, vector<double> &vTimestamps)
{
    ifstream fTimes;
    string strPathTimeFile = strPathToSequence + "/times.txt";
    fTimes.open(strPathTimeFile.c_str());
    while(!fTimes.eof())
    {
        string s;
        getline(fTimes,s);
        if(!s.empty())
        {
            stringstream ss;
            ss << s;
            double t;
            ss >> t;
            vTimestamps.push_back(t);
        }
    }

    string strPrefixLeft = strPathToSequence + "/image_0/";

    const int nTimes = vTimestamps.size();
    vstrImageFilenames.resize(nTimes);

    for(int i=0; i<nTimes; i++)
    {
        stringstream ss;
        ss << setfill('0') << setw(6) << i;
        vstrImageFilenames[i] = strPrefixLeft + ss.str() + ".png";
    }
}

这部分代码最主要的是读取图片并将图片送进SLAM系统，还有一些其他的比如说保存轨迹信息之类的后面再细讲。

 

以上都是个人理解，肯定有错误之处，也恳请大家帮忙指正，大家共同进步。