ORBSLAM2笔记(2)KeyFrame

void KeyFrame::SetBadFlag()函数图解

KeyFrame.h

/**
* This file is part of ORB-SLAM2.
*
* Copyright (C) 2014-2016 Raúl Mur-Artal <raulmur at unizar dot es> (University of Zaragoza)
* For more information see <https://github.com/raulmur/ORB_SLAM2>
*
* ORB-SLAM2 is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* ORB-SLAM2 is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with ORB-SLAM2. If not, see <http://www.gnu.org/licenses/>.
*/

#ifndef KEYFRAME_H
#define KEYFRAME_H

#include "MapPoint.h"
#include "Thirdparty/DBoW2/DBoW2/BowVector.h"
#include "Thirdparty/DBoW2/DBoW2/FeatureVector.h"
#include "ORBVocabulary.h"
#include "ORBextractor.h"
#include "Frame.h"
#include "KeyFrameDatabase.h"

#include <mutex>


namespace ORB_SLAM2
{

class Map;
class MapPoint;
class Frame;
class KeyFrameDatabase;


/**
 * 关键帧
 * 重要概念:
 * 1.Covisibility graph共视图:共视关键帧组成的图
 * 2.Spanning tree: Spaning tree是covisibility graph的子集,Spanning Tree中,和当前帧的共视程度最高的就是父节点
 * 3.
 */
class KeyFrame
{
public:
    KeyFrame(Frame &F, Map* pMap, KeyFrameDatabase* pKFDB);

    // Pose functions
    void SetPose(const cv::Mat &Tcw);
    cv::Mat GetPose();
    cv::Mat GetPoseInverse();
    cv::Mat GetCameraCenter();
    cv::Mat GetStereoCenter();
    cv::Mat GetRotation();
    cv::Mat GetTranslation();

    // Bag of Words Representation
    void ComputeBoW();

    // Covisibility graph functions
    void AddConnection(KeyFrame* pKF, const int &weight);
    void EraseConnection(KeyFrame* pKF);
    void UpdateConnections();
    void UpdateBestCovisibles();
    std::set<KeyFrame *> GetConnectedKeyFrames();
    std::vector<KeyFrame* > GetVectorCovisibleKeyFrames();
    std::vector<KeyFrame*> GetBestCovisibilityKeyFrames(const int &N);
    std::vector<KeyFrame*> GetCovisiblesByWeight(const int &w);
    int GetWeight(KeyFrame* pKF);

    // Spanning tree functions
    void AddChild(KeyFrame* pKF);
    void EraseChild(KeyFrame* pKF);
    void ChangeParent(KeyFrame* pKF);
    std::set<KeyFrame*> GetChilds();
    KeyFrame* GetParent();
    bool hasChild(KeyFrame* pKF);

    // Loop Edges
    void AddLoopEdge(KeyFrame* pKF);
    std::set<KeyFrame*> GetLoopEdges();

    // MapPoint observation functions
    void AddMapPoint(MapPoint* pMP, const size_t &idx);
    void EraseMapPointMatch(const size_t &idx);
    void EraseMapPointMatch(MapPoint* pMP);
    void ReplaceMapPointMatch(const size_t &idx, MapPoint* pMP);
    std::set<MapPoint*> GetMapPoints();
    std::vector<MapPoint*> GetMapPointMatches();
    int TrackedMapPoints(const int &minObs);
    MapPoint* GetMapPoint(const size_t &idx);

    // KeyPoint functions
    std::vector<size_t> GetFeaturesInArea(const float &x, const float  &y, const float  &r) const;
    cv::Mat UnprojectStereo(int i);

    // Image
    bool IsInImage(const float &x, const float &y) const;

    // Enable/Disable bad flag changes
    void SetNotErase();
    void SetErase();

    // Set/check bad flag
    void SetBadFlag();
    bool isBad();

    // Compute Scene Depth (q=2 median). Used in monocular.
    ///计算场景的深度中值
    float ComputeSceneMedianDepth(const int q);

    static bool weightComp( int a, int b){
        return a>b;
    }

    static bool lId(KeyFrame* pKF1, KeyFrame* pKF2){
        return pKF1->mnId<pKF2->mnId;
    }


    // The following variables are accesed from only 1 thread or never change (no mutex needed).
public:

    static long unsigned int nNextId;
    long unsigned int mnId;
    const long unsigned int mnFrameId;

    const double mTimeStamp;

    // Grid (to speed up feature matching)
    const int mnGridCols;
    const int mnGridRows;
    const float mfGridElementWidthInv;
    const float mfGridElementHeightInv;

    // Variables used by the tracking
    long unsigned int mnTrackReferenceForFrame;
    long unsigned int mnFuseTargetForKF;

    // Variables used by the local mapping
    long unsigned int mnBALocalForKF;
    long unsigned int mnBAFixedForKF;

    // Variables used by the keyframe database
    long unsigned int mnLoopQuery;
    int mnLoopWords;
    float mLoopScore;
    long unsigned int mnRelocQuery;
    int mnRelocWords;
    float mRelocScore;

    // Variables used by loop closing
    cv::Mat mTcwGBA;
    cv::Mat mTcwBefGBA;
    long unsigned int mnBAGlobalForKF;

    // Calibration parameters
    const float fx, fy, cx, cy, invfx, invfy, mbf, mb, mThDepth;

    // Number of KeyPoints
    const int N;

    // KeyPoints, stereo coordinate and descriptors (all associated by an index)
    const std::vector<cv::KeyPoint> mvKeys;
    const std::vector<cv::KeyPoint> mvKeysUn;
    const std::vector<float> mvuRight; // negative value for monocular points
    const std::vector<float> mvDepth; // negative value for monocular points
    const cv::Mat mDescriptors;

    //BoW
    DBoW2::BowVector mBowVec;
    /// std::map<NodeId, std::vector<unsigned int> >
    DBoW2::FeatureVector mFeatVec;

    // Pose relative to parent (this is computed when bad flag is activated)
    cv::Mat mTcp;

    // Scale
    const int mnScaleLevels;
    const float mfScaleFactor;
    const float mfLogScaleFactor;
    const std::vector<float> mvScaleFactors;
    const std::vector<float> mvLevelSigma2;
    const std::vector<float> mvInvLevelSigma2;

    // Image bounds and calibration
    const int mnMinX;
    const int mnMinY;
    const int mnMaxX;
    const int mnMaxY;
    const cv::Mat mK;


    // The following variables need to be accessed trough a mutex to be thread safe.
protected:

    // SE3 Pose and camera center
    cv::Mat Tcw;
    cv::Mat Twc;
    cv::Mat Ow;

    cv::Mat Cw; // Stereo middel point. Only for visualization

    // MapPoints associated to keypoints
    std::vector<MapPoint*> mvpMapPoints;

    // BoW
    KeyFrameDatabase* mpKeyFrameDB;
    ORBVocabulary* mpORBvocabulary;

    // Grid over the image to speed up feature matching
    std::vector< std::vector <std::vector<size_t> > > mGrid;

    ///key frame and it's weight
    std::map<KeyFrame*,int> mConnectedKeyFrameWeights;
    ///经过排列之后的从covisibility graph
    std::vector<KeyFrame*> mvpOrderedConnectedKeyFrames;
    ///从小到大排列的权重
    std::vector<int> mvOrderedWeights;

    // Spanning Tree and Loop Edges
    bool mbFirstConnection;
    KeyFrame* mpParent;
    std::set<KeyFrame*> mspChildrens;
    std::set<KeyFrame*> mspLoopEdges;

    // Bad flags
    bool mbNotErase;
    bool mbToBeErased;
    bool mbBad;    

    float mHalfBaseline; // Only for visualization

    Map* mpMap;

    std::mutex mMutexPose;
    std::mutex mMutexConnections;
    std::mutex mMutexFeatures;
};

} //namespace ORB_SLAM

#endif // KEYFRAME_H

/**
* This file is part of ORB-SLAM2.
*
* Copyright (C) 2014-2016 Raúl Mur-Artal <raulmur at unizar dot es> (University of Zaragoza)
* For more information see <https://github.com/raulmur/ORB_SLAM2>
*
* ORB-SLAM2 is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* ORB-SLAM2 is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with ORB-SLAM2. If not, see <http://www.gnu.org/licenses/>.
*/

#include "KeyFrame.h"
#include "Converter.h"
#include "ORBmatcher.h"
#include<mutex>

namespace ORB_SLAM2
{

long unsigned int KeyFrame::nNextId=0;

KeyFrame::KeyFrame(Frame &F, Map *pMap, KeyFrameDatabase *pKFDB):
    mnFrameId(F.mnId),  mTimeStamp(F.mTimeStamp), mnGridCols(FRAME_GRID_COLS), mnGridRows(FRAME_GRID_ROWS),
    mfGridElementWidthInv(F.mfGridElementWidthInv), mfGridElementHeightInv(F.mfGridElementHeightInv),
    mnTrackReferenceForFrame(0), mnFuseTargetForKF(0), mnBALocalForKF(0), mnBAFixedForKF(0),
    mnLoopQuery(0), mnLoopWords(0), mnRelocQuery(0), mnRelocWords(0), mnBAGlobalForKF(0),
    fx(F.fx), fy(F.fy), cx(F.cx), cy(F.cy), invfx(F.invfx), invfy(F.invfy),
    mbf(F.mbf), mb(F.mb), mThDepth(F.mThDepth), N(F.N), mvKeys(F.mvKeys), mvKeysUn(F.mvKeysUn),
    mvuRight(F.mvuRight), mvDepth(F.mvDepth), mDescriptors(F.mDescriptors.clone()),
    mBowVec(F.mBowVec), mFeatVec(F.mFeatVec), mnScaleLevels(F.mnScaleLevels), mfScaleFactor(F.mfScaleFactor),
    mfLogScaleFactor(F.mfLogScaleFactor), mvScaleFactors(F.mvScaleFactors), mvLevelSigma2(F.mvLevelSigma2),
    mvInvLevelSigma2(F.mvInvLevelSigma2), mnMinX(F.mnMinX), mnMinY(F.mnMinY), mnMaxX(F.mnMaxX),
    mnMaxY(F.mnMaxY), mK(F.mK), mvpMapPoints(F.mvpMapPoints), mpKeyFrameDB(pKFDB),
    mpORBvocabulary(F.mpORBvocabulary), mbFirstConnection(true), mpParent(NULL), mbNotErase(false),
    mbToBeErased(false), mbBad(false), mHalfBaseline(F.mb/2), mpMap(pMap)
{
    mnId=nNextId++;

    mGrid.resize(mnGridCols);
    for(int i=0; i<mnGridCols;i++)
    {
        mGrid[i].resize(mnGridRows);
        for(int j=0; j<mnGridRows; j++)
            mGrid[i][j] = F.mGrid[i][j];
    }

    SetPose(F.mTcw);    
}

/// compute keyframe's descriptors and insert into ORB vocabulary
void KeyFrame::ComputeBoW()
{
    if(mBowVec.empty() || mFeatVec.empty())
    {
        vector<cv::Mat> vCurrentDesc = Converter::toDescriptorVector(mDescriptors);
        // Feature vector associate features with nodes in the 4th level (from leaves up)
        // We assume the vocabulary tree has 6 levels, change the 4 otherwise
        mpORBvocabulary->transform(vCurrentDesc,mBowVec,mFeatVec,4);
    }
}

void KeyFrame::SetPose(const cv::Mat &Tcw_)
{
    unique_lock<mutex> lock(mMutexPose);
    Tcw_.copyTo(Tcw);
    cv::Mat Rcw = Tcw.rowRange(0,3).colRange(0,3);
    cv::Mat tcw = Tcw.rowRange(0,3).col(3);
    cv::Mat Rwc = Rcw.t();
    Ow = -Rwc*tcw;

    Twc = cv::Mat::eye(4,4,Tcw.type());
    Rwc.copyTo(Twc.rowRange(0,3).colRange(0,3));
    Ow.copyTo(Twc.rowRange(0,3).col(3));
    cv::Mat center = (cv::Mat_<float>(4,1) << mHalfBaseline, 0 , 0, 1);
    Cw = Twc*center;
}

cv::Mat KeyFrame::GetPose()
{
    unique_lock<mutex> lock(mMutexPose);
    return Tcw.clone();
}

cv::Mat KeyFrame::GetPoseInverse()
{
    unique_lock<mutex> lock(mMutexPose);
    return Twc.clone();
}

cv::Mat KeyFrame::GetCameraCenter()
{
    unique_lock<mutex> lock(mMutexPose);
    return Ow.clone();
}

cv::Mat KeyFrame::GetStereoCenter()
{
    unique_lock<mutex> lock(mMutexPose);
    return Cw.clone();
}


cv::Mat KeyFrame::GetRotation()
{
    unique_lock<mutex> lock(mMutexPose);
    return Tcw.rowRange(0,3).colRange(0,3).clone();
}

cv::Mat KeyFrame::GetTranslation()
{
    unique_lock<mutex> lock(mMutexPose);
    return Tcw.rowRange(0,3).col(3).clone();
}


void KeyFrame::AddConnection(KeyFrame *pKF, const int &weight)
{
    ///将新的关键帧和权重加入到共视图中
    {
        unique_lock<mutex> lock(mMutexConnections);
        if(!mConnectedKeyFrameWeights.count(pKF))
            mConnectedKeyFrameWeights[pKF]=weight;
        else if(mConnectedKeyFrameWeights[pKF]!=weight)
            mConnectedKeyFrameWeights[pKF]=weight;
        else
            return;
    }

    ///更新共视图
    UpdateBestCovisibles();
}

///将mConnectedKeyFrameWeights中的关键帧和权重提取出来放入vector,然后按照权重从小到大进行排列
///分别将关键帧和权重储存到mvpOrderedConnectedKeyFrames和mvOrderedWeights中
void KeyFrame::UpdateBestCovisibles()
{
    unique_lock<mutex> lock(mMutexConnections);
    vector<pair<int,KeyFrame*> > vPairs;
    vPairs.reserve(mConnectedKeyFrameWeights.size());
    for(map<KeyFrame*,int>::iterator mit=mConnectedKeyFrameWeights.begin(), mend=mConnectedKeyFrameWeights.end(); mit!=mend; mit++)
       vPairs.push_back(make_pair(mit->second,mit->first));

    sort(vPairs.begin(),vPairs.end());
    list<KeyFrame*> lKFs;
    list<int> lWs;
    for(size_t i=0, iend=vPairs.size(); i<iend;i++)
    {
        lKFs.push_front(vPairs[i].second);
        lWs.push_front(vPairs[i].first);
    }

    mvpOrderedConnectedKeyFrames = vector<KeyFrame*>(lKFs.begin(),lKFs.end());
    mvOrderedWeights = vector<int>(lWs.begin(), lWs.end());    
}

set<KeyFrame*> KeyFrame::GetConnectedKeyFrames()
{
    unique_lock<mutex> lock(mMutexConnections);
    set<KeyFrame*> s;
    for(map<KeyFrame*,int>::iterator mit=mConnectedKeyFrameWeights.begin();mit!=mConnectedKeyFrameWeights.end();mit++)
        s.insert(mit->first);
    return s;
}

vector<KeyFrame*> KeyFrame::GetVectorCovisibleKeyFrames()
{
    unique_lock<mutex> lock(mMutexConnections);
    return mvpOrderedConnectedKeyFrames;
}

vector<KeyFrame*> KeyFrame::GetBestCovisibilityKeyFrames(const int &N)
{
    unique_lock<mutex> lock(mMutexConnections);
    if((int)mvpOrderedConnectedKeyFrames.size()<N)
        return mvpOrderedConnectedKeyFrames;
    else
        return vector<KeyFrame*>(mvpOrderedConnectedKeyFrames.begin(),mvpOrderedConnectedKeyFrames.begin()+N);

}

vector<KeyFrame*> KeyFrame::GetCovisiblesByWeight(const int &w)
{
    unique_lock<mutex> lock(mMutexConnections);

    if(mvpOrderedConnectedKeyFrames.empty())
        return vector<KeyFrame*>();

    vector<int>::iterator it = upper_bound(mvOrderedWeights.begin(),mvOrderedWeights.end(),w,KeyFrame::weightComp);
    if(it==mvOrderedWeights.end())
        return vector<KeyFrame*>();
    else
    {
        int n = it-mvOrderedWeights.begin();
        return vector<KeyFrame*>(mvpOrderedConnectedKeyFrames.begin(), mvpOrderedConnectedKeyFrames.begin()+n);
    }
}

int KeyFrame::GetWeight(KeyFrame *pKF)
{
    unique_lock<mutex> lock(mMutexConnections);
    if(mConnectedKeyFrameWeights.count(pKF))
        return mConnectedKeyFrameWeights[pKF];
    else
        return 0;
}

void KeyFrame::AddMapPoint(MapPoint *pMP, const size_t &idx)
{
    unique_lock<mutex> lock(mMutexFeatures);
    mvpMapPoints[idx]=pMP;
}

void KeyFrame::EraseMapPointMatch(const size_t &idx)
{
    unique_lock<mutex> lock(mMutexFeatures);
    mvpMapPoints[idx]=static_cast<MapPoint*>(NULL);
}

void KeyFrame::EraseMapPointMatch(MapPoint* pMP)
{
    int idx = pMP->GetIndexInKeyFrame(this);
    if(idx>=0)
        mvpMapPoints[idx]=static_cast<MapPoint*>(NULL);
}


void KeyFrame::ReplaceMapPointMatch(const size_t &idx, MapPoint* pMP)
{
    mvpMapPoints[idx]=pMP;
}

set<MapPoint*> KeyFrame::GetMapPoints()
{
    unique_lock<mutex> lock(mMutexFeatures);
    set<MapPoint*> s;
    for(size_t i=0, iend=mvpMapPoints.size(); i<iend; i++)
    {
        if(!mvpMapPoints[i])
            continue;
        MapPoint* pMP = mvpMapPoints[i];
        if(!pMP->isBad())
            s.insert(pMP);
    }
    return s;
}

///统计被追踪到的地图点,当地图点的观测帧的数目大于等于minObs,被认为已经追踪到了该地图点
int KeyFrame::TrackedMapPoints(const int &minObs)
{
    unique_lock<mutex> lock(mMutexFeatures);

    int nPoints=0;
    const bool bCheckObs = minObs>0;
    for(int i=0; i<N; i++)
    {
        MapPoint* pMP = mvpMapPoints[i];
        if(pMP)
        {
            if(!pMP->isBad())
            {
                if(bCheckObs)
                {
                    if(mvpMapPoints[i]->Observations()>=minObs)
                        nPoints++;
                }
                else
                    nPoints++;
            }
        }
    }

    return nPoints;
}

vector<MapPoint*> KeyFrame::GetMapPointMatches()
{
    unique_lock<mutex> lock(mMutexFeatures);
    return mvpMapPoints;
}

MapPoint* KeyFrame::GetMapPoint(const size_t &idx)
{
    unique_lock<mutex> lock(mMutexFeatures);
    return mvpMapPoints[idx];
}

/**
 * 更新共视图的关系
 * 统计当前帧和其它帧之间的共视3D点的数目,如果大于一定阈值,就在两个关键帧之间增加一条共视边
 */
void KeyFrame::UpdateConnections()
{
    ///和当前关键帧有共视关系的关键帧以及共视点的数目
    map<KeyFrame*,int> KFcounter;

    ///取出所有的MapPoint
    vector<MapPoint*> vpMP;

    {
        unique_lock<mutex> lockMPs(mMutexFeatures);
        vpMP = mvpMapPoints;
    }

    //For all map points in keyframe check in which other keyframes are they seen
    //Increase counter for those keyframes
    /**
     * 1.获取当前关键帧的所有MapPoint,并进行遍历;
     * 2.遍历得到每个MapPoint的观测帧,统计其它帧和当前帧的共视点的数目,并储存在KFcounter中.
     **/
    for(vector<MapPoint*>::iterator vit=vpMP.begin(), vend=vpMP.end(); vit!=vend; vit++)
    {
        MapPoint* pMP = *vit;

        if(!pMP)
            continue;

        if(pMP->isBad())
            continue;

        ///获取MapPoint的所有的观测帧
        map<KeyFrame*,size_t> observations = pMP->GetObservations();

        ///遍历观测到该点的观测帧
        for(map<KeyFrame*,size_t>::iterator mit=observations.begin(), mend=observations.end(); mit!=mend; mit++)
        {
            if(mit->first->mnId==mnId)
                continue;
            KFcounter[mit->first]++;
        }
    }

    // This should not happen
    ///该帧和其它帧没有共视关系
    if(KFcounter.empty())
        return;

    //If the counter is greater than threshold add connection
    //In case no keyframe counter is over threshold add the one with maximum counter
    ///如果其它帧和当前帧的共视的MapPoint的数目大于15,那么就增加一条共视边;
    ///为了防止没有超过达到阈值的关键帧,添加拥有最多共视MapPoint的帧作为共视边
    int nmax=0;
    KeyFrame* pKFmax=NULL;
    int th = 15;

    vector<pair<int,KeyFrame*> > vPairs;
    vPairs.reserve(KFcounter.size());
    for(map<KeyFrame*,int>::iterator mit=KFcounter.begin(), mend=KFcounter.end(); mit!=mend; mit++)
    {
        if(mit->second>nmax)
        {
            nmax=mit->second;
            pKFmax=mit->first;
        }
        if(mit->second>=th)
        {
            vPairs.push_back(make_pair(mit->second,mit->first));
            (mit->first)->AddConnection(this,mit->second);
        }
    }

    if(vPairs.empty())
    {
        vPairs.push_back(make_pair(nmax,pKFmax));
        pKFmax->AddConnection(this,nmax);
    }

    ///根据共视程度进行从小大小的排列
    sort(vPairs.begin(),vPairs.end());
    list<KeyFrame*> lKFs;
    list<int> lWs;
    //权重大的放前面
    for(size_t i=0; i<vPairs.size();i++)
    {
        lKFs.push_front(vPairs[i].second);
        lWs.push_front(vPairs[i].first);
    }

    {
        unique_lock<mutex> lockCon(mMutexConnections);

        // mspConnectedKeyFrames = spConnectedKeyFrames;
        mConnectedKeyFrameWeights = KFcounter;
        mvpOrderedConnectedKeyFrames = vector<KeyFrame*>(lKFs.begin(),lKFs.end());
        mvOrderedWeights = vector<int>(lWs.begin(), lWs.end());

        if(mbFirstConnection && mnId!=0)
        {
            ///和当前关键帧共视程度最高的帧作为spanning tree的父节点
            mpParent = mvpOrderedConnectedKeyFrames.front();
            mpParent->AddChild(this);
            mbFirstConnection = false;
        }

    }
}

void KeyFrame::AddChild(KeyFrame *pKF)
{
    unique_lock<mutex> lockCon(mMutexConnections);
    mspChildrens.insert(pKF);
}

void KeyFrame::EraseChild(KeyFrame *pKF)
{
    unique_lock<mutex> lockCon(mMutexConnections);
    mspChildrens.erase(pKF);
}

///换一个爸爸节点
void KeyFrame::ChangeParent(KeyFrame *pKF)
{
    unique_lock<mutex> lockCon(mMutexConnections);
    mpParent = pKF;
    pKF->AddChild(this);
}

///获取子节点
set<KeyFrame*> KeyFrame::GetChilds()
{
    unique_lock<mutex> lockCon(mMutexConnections);
    return mspChildrens;
}

KeyFrame* KeyFrame::GetParent()
{
    unique_lock<mutex> lockCon(mMutexConnections);
    return mpParent;
}

bool KeyFrame::hasChild(KeyFrame *pKF)
{
    unique_lock<mutex> lockCon(mMutexConnections);
    return mspChildrens.count(pKF);
}


///在当前帧和pKF帧之间添加一条回环的边
void KeyFrame::AddLoopEdge(KeyFrame *pKF)
{
    unique_lock<mutex> lockCon(mMutexConnections);
    mbNotErase = true;
    mspLoopEdges.insert(pKF);
}

set<KeyFrame*> KeyFrame::GetLoopEdges()
{
    unique_lock<mutex> lockCon(mMutexConnections);
    return mspLoopEdges;
}

void KeyFrame::SetNotErase()
{
    unique_lock<mutex> lock(mMutexConnections);
    mbNotErase = true;
}

void KeyFrame::SetErase()
{
    {
        unique_lock<mutex> lock(mMutexConnections);
        if(mspLoopEdges.empty())
        {
            mbNotErase = false;
        }
    }

    if(mbToBeErased)
    {
        SetBadFlag();
    }
}

/**
 * 设置当前关键帧badflag,这个函数主要处理当需要剔除某些关键帧的时候,
 * 如何更新这个关键帧和其它关键帧的共视关系.
 * 
 */
void KeyFrame::SetBadFlag()
{   
    {
        unique_lock<mutex> lock(mMutexConnections);
        if(mnId==0)
            return;
        else if(mbNotErase)
        {
            mbToBeErased = true;
            return;
        }
    }

    ///1.遍历和该帧有共视关系的所有帧,删除和它们和该帧的共视关系
    for(map<KeyFrame*,int>::iterator mit = mConnectedKeyFrameWeights.begin(), mend=mConnectedKeyFrameWeights.end(); mit!=mend; mit++)
        mit->first->EraseConnection(this);

    ///2.遍历该关键帧的所有MapPoint,该帧的不再作为相应MapPoint的观测帧
    for(size_t i=0; i<mvpMapPoints.size(); i++)
        if(mvpMapPoints[i])
            mvpMapPoints[i]->EraseObservation(this);
    
    {
        unique_lock<mutex> lock(mMutexConnections);
        unique_lock<mutex> lock1(mMutexFeatures);

        ///清除其共视图和权重
        mConnectedKeyFrameWeights.clear();
        mvpOrderedConnectedKeyFrames.clear();

        // Update Spanning Tree
        ///候选父节点
        set<KeyFrame*> sParentCandidates;
        ///将当前帧的父节点加入候选父节点
        sParentCandidates.insert(mpParent);

        // Assign at each iteration one children with a parent (the pair with highest covisibility weight)
        // Include that children as new parent candidate for the rest
        ///3.每次处理一个child节点,给这个child节点寻找一个与其共视程度最高的新父节点
        while(!mspChildrens.empty())
        {
            bool bContinue = false;

            int max = -1;
            KeyFrame* pC;///pointer to Child Key Frame
            KeyFrame* pP; /// pointer to Parent Key Frame

            ///4.遍历这个关键帧的所有子节点,给每个子节点重新找一个共视程度最高的父节点
            for(set<KeyFrame*>::iterator sit=mspChildrens.begin(), send=mspChildrens.end(); sit!=send; sit++)
            {
                ///取出一个子节点
                KeyFrame* pKF = *sit;
                if(pKF->isBad())
                    continue;

                // Check if a parent candidate is connected to the keyframe
                ///找出该子节点的所有共视帧
                vector<KeyFrame*> vpConnected = pKF->GetVectorCovisibleKeyFrames();
                ///5.遍历共视帧
                for(size_t i=0, iend=vpConnected.size(); i<iend; i++)
                {
                    ///6.遍历候选父节点
                    for(set<KeyFrame*>::iterator spcit=sParentCandidates.begin(), spcend=sParentCandidates.end(); spcit!=spcend; spcit++)
                    {
                        ///7.如果子节点的共视帧恰好是候选父节点帧
                        if(vpConnected[i]->mnId == (*spcit)->mnId)
                        {
                            int w = pKF->GetWeight(vpConnected[i]);
                            if(w>max)
                            {
                                pC = pKF;
                                pP = vpConnected[i];
                                max = w;
                                bContinue = true;
                            }
                        }
                    }
                }
            } ///for loop every child

            if(bContinue)
            {
                ///8.子节点找到新的父节点,就换成新的父节点
                pC->ChangeParent(pP);
                ///9.将新的子节点作为候选的父节点
                sParentCandidates.insert(pC);
                ///10.当前子节点不再作为当前帧的子节点
                mspChildrens.erase(pC);
            }
            else
                break;
        }//while

        // 11.If a children has no covisibility links with any parent candidate, assign to the original parent of this KF
        if(!mspChildrens.empty())
            for(set<KeyFrame*>::iterator sit=mspChildrens.begin(); sit!=mspChildrens.end(); sit++)
            {
                (*sit)->ChangeParent(mpParent);
            }

        mpParent->EraseChild(this);
        mTcp = Tcw*mpParent->GetPoseInverse();
        mbBad = true;
    }


    ///在地图中删除该关键帧
    mpMap->EraseKeyFrame(this);
    ///在关键帧数据库中删除该关键帧
    mpKeyFrameDB->erase(this);
}

bool KeyFrame::isBad()
{
    unique_lock<mutex> lock(mMutexConnections);
    return mbBad;
}

///删除当前帧和pKF帧的共视关系
void KeyFrame::EraseConnection(KeyFrame* pKF)
{
    bool bUpdate = false;
    {
        unique_lock<mutex> lock(mMutexConnections);
        if(mConnectedKeyFrameWeights.count(pKF))
        {
            mConnectedKeyFrameWeights.erase(pKF);
            bUpdate=true;
        }
    }

    if(bUpdate)
        UpdateBestCovisibles();
}

///获取以x,y为矩形中心,r为矩形边长范围内的特征点
vector<size_t> KeyFrame::GetFeaturesInArea(const float &x, const float &y, const float &r) const
{
    vector<size_t> vIndices;
    vIndices.reserve(N);

    const int nMinCellX = max(0,(int)floor((x-mnMinX-r)*mfGridElementWidthInv));
    if(nMinCellX>=mnGridCols)
        return vIndices;

    const int nMaxCellX = min((int)mnGridCols-1,(int)ceil((x-mnMinX+r)*mfGridElementWidthInv));
    if(nMaxCellX<0)
        return vIndices;

    const int nMinCellY = max(0,(int)floor((y-mnMinY-r)*mfGridElementHeightInv));
    if(nMinCellY>=mnGridRows)
        return vIndices;

    const int nMaxCellY = min((int)mnGridRows-1,(int)ceil((y-mnMinY+r)*mfGridElementHeightInv));
    if(nMaxCellY<0)
        return vIndices;

    for(int ix = nMinCellX; ix<=nMaxCellX; ix++)
    {
        for(int iy = nMinCellY; iy<=nMaxCellY; iy++)
        {
            const vector<size_t> vCell = mGrid[ix][iy];
            for(size_t j=0, jend=vCell.size(); j<jend; j++)
            {
                const cv::KeyPoint &kpUn = mvKeysUn[vCell[j]];
                const float distx = kpUn.pt.x-x;
                const float disty = kpUn.pt.y-y;

                if(fabs(distx)<r && fabs(disty)<r)
                    vIndices.push_back(vCell[j]);
            }
        }
    }

    return vIndices;
}

bool KeyFrame::IsInImage(const float &x, const float &y) const
{
    return (x>=mnMinX && x<mnMaxX && y>=mnMinY && y<mnMaxY);
}

cv::Mat KeyFrame::UnprojectStereo(int i)
{
    const float z = mvDepth[i];
    if(z>0)
    {
        const float u = mvKeys[i].pt.x;
        const float v = mvKeys[i].pt.y;
        const float x = (u-cx)*z*invfx;
        const float y = (v-cy)*z*invfy;
        cv::Mat x3Dc = (cv::Mat_<float>(3,1) << x, y, z);

        unique_lock<mutex> lock(mMutexPose);
        return Twc.rowRange(0,3).colRange(0,3)*x3Dc+Twc.rowRange(0,3).col(3);
    }
    else
        return cv::Mat();
}

float KeyFrame::ComputeSceneMedianDepth(const int q)
{
    ///获取当前关键帧的所有MapPoint
    vector<MapPoint*> vpMapPoints;
    cv::Mat Tcw_;
    {
        unique_lock<mutex> lock(mMutexFeatures);
        unique_lock<mutex> lock2(mMutexPose);
        vpMapPoints = mvpMapPoints;
        Tcw_ = Tcw.clone();
    }

    ///将所有的MapPoint转换到相机坐标系,并将深度信息储存到vDepths中
    vector<float> vDepths;
    vDepths.reserve(N);
    cv::Mat Rcw2 = Tcw_.row(2).colRange(0,3);
    Rcw2 = Rcw2.t();
    float zcw = Tcw_.at<float>(2,3);
    for(int i=0; i<N; i++)
    {
        if(mvpMapPoints[i])
        {
            MapPoint* pMP = mvpMapPoints[i];
            /// map point's 3D pose
            cv::Mat x3Dw = pMP->GetWorldPos();
            /// translate to camera frame
            float z = Rcw2.dot(x3Dw)+zcw;
            vDepths.push_back(z);
        }
    }

    ///按照大小排列
    sort(vDepths.begin(),vDepths.end());

    ///q=2,则意味着取中值
    return vDepths[(vDepths.size()-1)/q];
}

} //namespace ORB_SLAM