highlyreliablemarkers.cpp

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/*****************************
Copyright 2011 Rafael Muñoz Salinas. All rights reserved.

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********************************/

#include <aruco/highlyreliablemarkers.h>

namespace aruco {

  // static variables from HighlyReliableMarkers. Need to be here to avoid linking errors
  Dictionary HighlyReliableMarkers::_D;
  HighlyReliableMarkers::BalancedBinaryTree HighlyReliableMarkers::_binaryTree;
  unsigned int HighlyReliableMarkers::_n, HighlyReliableMarkers::_ncellsBorder, HighlyReliableMarkers::_correctionDistance;
  int HighlyReliableMarkers::_swidth;


  MarkerCode::MarkerCode(unsigned int n) {
    // resize bits vectors and initialize to 0
    for(unsigned int i=0; i<4; i++) {
      _bits[i].resize(n*n); 
      for(unsigned int j=0; j<_bits[i].size(); j++) _bits[i][j]=0;
      _ids[i] = 0; // ids are also 0
    }
    _n = n;
  };
  
  
  MarkerCode::MarkerCode(const MarkerCode& MC)
  {
    for(unsigned int i=0; i<4; i++) {
      _bits[i] = MC._bits[i];
      _ids[i] = MC._ids[i];
    }
    _n = MC._n;
  }

  
  
  void MarkerCode::set(unsigned int pos, bool val) {
    // if not the same value
    if( get(pos) != val ) {
      for(unsigned int i=0; i<4; i++) { // calculate bit coordinates for each rotation
    unsigned int y=pos/n(), x=pos%n(); // if rotation 0, dont do anything
        // else calculate bit position in that rotation
    if(i==1) { unsigned int aux=y; y=x; x=n()-aux-1; }
        else if(i==2) { y=n()-y-1; x=n()-x-1; }
    else if(i==3) { unsigned int aux=y; y=n()-x-1; x=aux; }
    unsigned int rotPos = y*n()+x; // calculate position in the unidimensional string
        _bits[i][rotPos] = val; // modify value
        // update identifier in that rotation
    if(val==true) _ids[i] += (unsigned int)pow(float(2),float(rotPos)); // if 1, add 2^pos
    else _ids[i] -= (unsigned int)pow(float(2),float(rotPos)); // if 0, substract 2^pos
      }   
    }
  }
  
  
  unsigned int MarkerCode::selfDistance(unsigned int &minRot) {
    unsigned int res = _bits[0].size(); // init to n*n (max value)
    for(unsigned int i=1; i<4; i++) { // self distance is not calculated for rotation 0
      unsigned int hammdist = hammingDistance(_bits[0], _bits[i]);
      if(hammdist<res) {
        minRot = i;
        res = hammdist;
      }
    }
    return res;
  }
  
  
  unsigned int MarkerCode::distance(MarkerCode m, unsigned int &minRot) {
    unsigned int res = _bits[0].size(); // init to n*n (max value)
    for(unsigned int i=0; i<4; i++) {
      unsigned int hammdist = hammingDistance(_bits[0], m.getRotation(i));
      if(hammdist<res) {
        minRot = i;
        res = hammdist;
      }      
    }
    return res;    
  };
  

  void MarkerCode::fromString(std::string s)
  {
    for(unsigned int i=0; i<s.length(); i++) {
      if(s[i]=='0') set(i, false);
      else set(i, true);
    }
  }

  std::string MarkerCode::toString()
  {
    std::string s;
    s.resize(size());
    for(unsigned int i=0; i<size(); i++) {
      if(get(i)) s[i]='1';
      else s[i]='0';
    }
    return s;
  }  
  
  
  cv::Mat MarkerCode::getImg(unsigned int pixSize) {
    const unsigned int borderSize=1;
    unsigned int nrows = n()+2*borderSize;
    if(pixSize%nrows != 0) pixSize = pixSize + nrows - pixSize%nrows;
    unsigned int cellSize = pixSize / nrows;
    cv::Mat img(pixSize, pixSize, CV_8U, cv::Scalar::all(0)); // create black image (init image to 0s)
    // double for to go over all the cells
    for(unsigned int i=0; i<n(); i++) {
      for(unsigned int j=0; j<n(); j++) {
        if(_bits[0][i*n()+j]!=0) { // just draw if it is 1, since the image has been init to 0
          // double for to go over all the pixels in the cell
      for(unsigned int k=0; k<cellSize; k++) {
        for(unsigned int l=0; l<cellSize; l++) {
              img.at<uchar>((i+borderSize)*cellSize+k, (j+borderSize)*cellSize+l) = 255;
            }
          }
        }
      }
    }
    return img;    
  }  
  
  
  unsigned int MarkerCode::hammingDistance(std::vector<bool> m1, std::vector<bool> m2) {
    unsigned int res=0;
    for(unsigned int i=0; i<m1.size(); i++)
      if(m1[i]!=m2[i]) res++;
    return res;
  };  
  
  
  
  
  
  
  bool Dictionary::fromFile(std::string filename) {
    cv::FileStorage fs(filename, cv::FileStorage::READ);
    int nmarkers, markersize;
    
    // read number of markers
    fs["nmarkers"] >> nmarkers; // cardinal of D
    fs["markersize"] >> markersize; // n
       
    // read each marker info
    for (int i=0; i<nmarkers; i++) {  
        std::string s;
        fs["marker_" + toStr(i)] >> s;
        MarkerCode m(markersize);
        m.fromString(s);
        push_back(m);
    }
    fs.release();   
    return true;
  };
  
  bool Dictionary::toFile(std::string filename) {
    cv::FileStorage fs(filename, cv::FileStorage::WRITE);
    // save number of markers
    fs << "nmarkers" << (int)size(); // cardinal of D 
    fs << "markersize" << (int)( (*this)[0].n() ); // n
    // save each marker code
    for (unsigned int i=0; i<size(); i++) {
        std::string s =  ((*this)[i]).toString();
        fs << "marker_" + toStr(i) << s;
    }
    fs.release();  
    return true;
  };
  
  unsigned int Dictionary::distance(MarkerCode m, unsigned int &minMarker, unsigned int &minRot) {
    unsigned int res = m.size();
    for(unsigned int i=0; i<size(); i++) {
      unsigned int minRotAux;
      unsigned int distance = (*this)[i].distance(m, minRotAux);
      if(distance<res) {
        minMarker = i;
        minRot = minRotAux;
        res=distance;
      }
    }
    return res;
  }
  
  
  unsigned int Dictionary::minimunDistance()
  {
    if(size()==0) return 0;
    unsigned int minDist = (*this)[0].size();
    // for each marker in D
    for(unsigned int i=0; i<size(); i++) {
      // calculate self distance of the marker
      minDist = std::min( minDist, (*this)[i].selfDistance() );
      
      // calculate distance to all the following markers
      for(unsigned int j=i+1; j<size(); j++) {
        minDist = std::min( minDist, (*this)[i].distance((*this)[j]) );
      }
    }
    return minDist;
  }
  
  
  
  
  
  
  
  
  
  
  bool HighlyReliableMarkers::loadDictionary(Dictionary D){  
    if(D.size()==0) return false;
    _D = D;
    _n = _D[0].n();
    _ncellsBorder = (_D[0].n()+2);
    _correctionDistance = (unsigned int)floor( (_D.minimunDistance()-1)/2. ); //maximun correction distance
    
    _binaryTree.loadDictionary(&D);   
    
    return true;
    
  };
  
  bool HighlyReliableMarkers::loadDictionary(std::string filename){ 
    Dictionary D;
    D.fromFile(filename); 
    return loadDictionary(D);
  };  
    
  
  int HighlyReliableMarkers::detect(const cv::Mat& in, int& nRotations)
  {  

    assert(in.rows==in.cols);
    cv::Mat grey;
    if ( in.type()==CV_8UC1) grey=in;
    else cv::cvtColor(in,grey,CV_BGR2GRAY);
    //threshold image
    cv::threshold(grey, grey,125, 255, cv::THRESH_BINARY|cv::THRESH_OTSU);
    _swidth=grey.rows/_ncellsBorder;    
    
    // check borders, even not necesary for the highly reliable markers
    //if(!checkBorders(grey)) return -1; 
    
    // obtain inner code
    MarkerCode candidate = getMarkerCode(grey);

    // search each marker id in the balanced binary tree
    unsigned int orgPos;
    for(unsigned int i=0; i<4; i++) {
      if(_binaryTree.findId( candidate.getId(i), orgPos )) {
          nRotations = i;
          return candidate.getId(i);
          //return orgPos;
      }
    }
    
    // alternative version without using the balanced binary tree (less eficient)
    //     for(uint i=0; i<_D.size(); i++) {
    //       for(uint j=0; j<4; j++) {
    //  if(_D[i].getId() == candidate.getId(j)) {
    //    nRotations = j;
    //    return candidate.getId(j);
    //  }
    //       }
    //     }
    
    // correct errors
    unsigned int minMarker, minRot;
    if(_D.distance(candidate, minMarker, minRot) <= _correctionDistance) {
      nRotations = minRot;
      //return minMarker;
     return _D[minMarker].getId();
    }
        
    return -1;

  }  
  
  
  bool HighlyReliableMarkers::checkBorders(cv::Mat grey) {
    for (int y=0;y<_ncellsBorder;y++)
    {
        int inc=_ncellsBorder-1;
        if (y==0 || y==_ncellsBorder-1) inc=1;//for first and last row, check the whole border
        for (int x=0;x<_ncellsBorder;x+=inc)
        {
            int Xstart=(x)*(_swidth);
            int Ystart=(y)*(_swidth);
            cv::Mat square=grey(cv::Rect(Xstart,Ystart,_swidth,_swidth));
            int nZ=cv::countNonZero(square);
            if (nZ> (_swidth*_swidth) /2) {
                return false;//can not be a marker because the border element is not black!
            }
        }
    }    
    return true;
  }
  
  MarkerCode HighlyReliableMarkers::getMarkerCode(cv::Mat grey) {
    MarkerCode candidate( _n );
    for (int y=0;y<_n;y++)
    {
        for (int x=0;x<_n;x++)
        {
            int Xstart=(x+1)*(_swidth);
            int Ystart=(y+1)*(_swidth);
            cv::Mat square=grey(cv::Rect(Xstart,Ystart,_swidth,_swidth));
            int nZ=countNonZero(square);
            if (nZ> (_swidth*_swidth) /2)  candidate.set(y*_n+x, 1);
        }
     } 
     return candidate;
   };
   
   
  
  void HighlyReliableMarkers::BalancedBinaryTree::loadDictionary(Dictionary *D) {
    // create _orderD wich is a sorted version of D
    _orderD.clear();
    for(unsigned int i=0; i<D->size(); i++) {
      _orderD.push_back( std::pair<unsigned int,unsigned int>( (*D)[i].getId() ,i) );
    }
    std::sort(_orderD.begin(), _orderD.end());
    
    // calculate the number of levels of the tree 
    unsigned int levels=0;
    while( pow(float(2),float(levels)) <= _orderD.size() ) levels++;
    //       levels-=1; // only count full levels
    
    // auxiliar vector to know which elements are already in the tree
    std::vector<bool> visited;
    visited.resize(_orderD.size());
    for(unsigned int i=0; i<_orderD.size(); i++) visited[i]=false;
    
    // calculate position of the root element
    unsigned int rootIdx = _orderD.size()/2;
    visited[rootIdx] = true; // mark it as visited
    
    // auxiliar vector to store the ids intervals (max and min) during the creation of the tree
    std::vector< std::pair<unsigned int, unsigned int> > intervals;
    // first, add the two intervals at each side of root element
    intervals.push_back( std::pair<unsigned int, unsigned int>(0,rootIdx) );
    intervals.push_back( std::pair<unsigned int, unsigned int>(rootIdx,_orderD.size()) );

    // init the tree
    _binaryTree.clear();
    _binaryTree.resize(_orderD.size());
    
    // add root information to the tree (make sure child do not coincide with self root for small sizes of D)
    if(!visited[(0+rootIdx)/2]) _binaryTree[rootIdx].first = (0+rootIdx)/2;
    else _binaryTree[rootIdx].first = -1;
    if(!visited[(rootIdx+_orderD.size())/2]) _binaryTree[rootIdx].second = (rootIdx+_orderD.size())/2;
    else _binaryTree[rootIdx].second = -1;
            
    // for each tree level
    for(unsigned int i=1; i<levels; i++) {
      unsigned int nintervals = intervals.size(); // count number of intervals and process them
      for(unsigned int j=0; j<nintervals; j++) {
        // store interval information and delete it
    unsigned int lowerBound, higherBound;
        lowerBound = intervals.back().first;
        higherBound = intervals.back().second;
        intervals.pop_back();
        
        // center of the interval
    unsigned int center = (higherBound + lowerBound)/2;
        
        // if center not visited, continue
        if(!visited[center])    visited[center]=true;
        else continue;
        
        // calculate centers of the child intervals
    unsigned int lowerChild = (lowerBound + center)/2;
    unsigned int higherChild = (center + higherBound)/2;
        
        // if not visited (lower child)
        if(!visited[lowerChild]) {
      intervals.insert( intervals.begin(), std::pair<unsigned int, unsigned int>(lowerBound, center) ); // add the interval to analyze later
          _binaryTree[center].first = lowerChild; // add as a child in the tree
        }
        else _binaryTree[center].first = -1; // if not, mark as no child

        // (higher child, same as lower child)
        if(!visited[higherChild]) {
      intervals.insert( intervals.begin(), std::pair<unsigned int, unsigned int>(center, higherBound) );
          _binaryTree[center].second = higherChild;
        }
        else _binaryTree[center].second = -1;
        
      }
    }      
    
    // print tree
    // for(uint i=0; i<_binaryTree.size(); i++) std::cout << _binaryTree[i].first << " " << _binaryTree[i].second << std::endl;
    // std::cout << std::endl;
    
  };   
  
  
  bool HighlyReliableMarkers::BalancedBinaryTree::findId(unsigned int id, unsigned int &orgPos) {
    unsigned int pos = _root; // first position is root
    while(pos!=-1) { // while having a valid position
      unsigned int posId = _orderD[pos].first; // calculate id of the node
      if(posId == id ) {
        orgPos = _orderD[pos].second;
        return true; // if is the desire id, return true
      }
      else if(posId < id) pos = _binaryTree[pos].second; // if desired id is higher, look in higher child
      else pos = _binaryTree[pos].first; // if it is lower, look in lower child
    }
    return false; // if nothing found, return false
  }
  
  
};