/*****************************************************************************
 *   Marker.cpp
 *   Example_MarkerBasedAR
 ******************************************************************************
 *   by Khvedchenia Ievgen, 5th Dec 2012
 *   http://computer-vision-talks.com
 ******************************************************************************
 *   Ch2 of the book "Mastering OpenCV with Practical Computer Vision Projects"
 *   Copyright Packt Publishing 2012.
 *   http://www.packtpub.com/cool-projects-with-opencv/book
 *****************************************************************************/

#include "Marker.hpp"
#include "DebugHelpers.hpp"

Marker::Marker()
: id(-1)// id初始化為-1
{
}

// 過載了‘<’運算子
bool operator<(const Marker &M1,const Marker&M2)
{
    return M1.id<M2.id;
}

// 順時針旋轉標記矩陣
cv::Mat Marker::rotate(cv::Mat in)
{
    cv::Mat out;
    in.copyTo(out);
    for (int i=0;i<in.rows;i++)
    {
        for (int j=0;j<in.cols;j++)
        {
            out.at<uchar>(i,j)=in.at<uchar>(in.cols-j-1,i);
        }
    }
    return out;
}

// 計算標記矩陣的海明距離
int Marker::hammDistMarker(cv::Mat bits)
{
    // bits中的每一行，都要與ids中的所有行進行比較
    int ids[4][5]=
    {
        // id的順序無所謂
        {1,0,0,0,0},
        {1,0,1,1,1},
        {0,1,0,0,1},
        {0,1,1,1,0}
    };
    
    int dist=0;
    
    // rows
    for (int y=0;y<5;y++)
    {
        int minSum=1e5; // hamming distance to each possible word
        
        for (int p=0;p<4;p++)
        {
            int sum=0;
            // 統計海明距離
            // cols
            for (int x=0;x<5;x++)
            {
                sum += (bits.at<uchar>(y,x) == ids[p][x]) ? 0 : 1;
            }
            // 求bits中第y行與ids中第p行的最小距離
            if (minSum>sum)
                minSum=sum;
        }
        
        // 計算bits中所有行的總距離
        dist += minSum;
    }
    
    return dist;
}

// mat轉id
int Marker::mat2id(const cv::Mat &bits)
{
    int val=0;
    for (int y=0;y<5;y++)
    {
        val<<=1;// val=val<<1
        // 只有1和3位是有用的，其他3位（0 2 4）是校驗位
        if ( bits.at<uchar>(y,1)) val|=1;
        val<<=1;
        if ( bits.at<uchar>(y,3)) val|=1;
    }
    return val;
}

int Marker::getMarkerId(cv::Mat &markerImage,int &nRotations)
{
    assert(markerImage.rows == markerImage.cols);
    assert(markerImage.type() == CV_8UC1);
    
    cv::Mat grey = markerImage;
    
    // Threshold image
    cv::threshold(grey, grey, 125, 255, cv::THRESH_BINARY | cv::THRESH_OTSU);
    
#ifdef SHOW_DEBUG_IMAGES
    cv::showAndSave("Binary marker", grey);
#endif
    
    //Markers  are divided in 7x7 regions, of which the inner 5x5 belongs to marker info
    //the external border should be entirely black
    // 檢測是否是標記的邊界
    int cellSize = markerImage.rows / 7;
    
    for (int y=0;y<7;y++)
    {
        int inc=6;
        
        if (y==0 || y==6) inc=1; //for first and last row, check the whole border
        
        for (int x=0;x<7;x+=inc)
        {
            int cellX = x * cellSize;
            int cellY = y * cellSize;
            // 在grey矩陣中取ROI矩陣
            cv::Mat cell = grey(cv::Rect(cellX,cellY,cellSize,cellSize));
            
            int nZ = cv::countNonZero(cell);
            
            if (nZ > (cellSize*cellSize) / 2)
            {
                return -1;//can not be a marker because the border element is not black!
            }
        }
    }
    
    cv::Mat bitMatrix = cv::Mat::zeros(5,5,CV_8UC1);
    
    //get information(for each inner square, determine if it is  black or white)
    // 根據5*5的黑白格子元素來設定bitMatrix矩陣：白色=1 黑色=0
    for (int y=0;y<5;y++)
    {
        for (int x=0;x<5;x++)
        {   // 從5*5的第一個格子開始
            int cellX = (x+1)*cellSize;
            int cellY = (y+1)*cellSize;
            // 在grey矩陣中取ROI矩陣
            cv::Mat cell = grey(cv::Rect(cellX,cellY,cellSize,cellSize));
            
            int nZ = cv::countNonZero(cell);
            if (nZ> (cellSize*cellSize) /2)
                bitMatrix.at<uchar>(y,x) = 1;
        }
    }
    
    //check all possible rotations
    cv::Mat rotations[4];
    int distances[4];
    
    rotations[0] = bitMatrix;
    distances[0] = hammDistMarker(rotations[0]);
    // 將第一個標記的海明距離作為最小距離
    // 鍵值對裡存的時 1.最小距離 2.對應標記的索引
    std::pair<int,int> minDist(distances[0],0);
    
    for (int i=1; i<4; i++)
    {
        //get the hamming distance to the nearest possible word
        // 將其餘的三種旋轉可能標記的海明距離與最小距離進行比較ß
        rotations[i] = rotate(rotations[i-1]);
        distances[i] = hammDistMarker(rotations[i]);

        if (distances[i] < minDist.first)
        {
            minDist.first  = distances[i];
            minDist.second = i;
        }
    }
    // 儲存識別出的標記的索引
    nRotations = minDist.second;
    if (minDist.first == 0)
    {
        return mat2id(rotations[minDist.second]);
    }
    
    return -1;
}

void Marker::drawContour(cv::Mat& image, cv::Scalar color) const
{
    float thickness = 2;
    
    cv::line(image, points[0], points[1], color, thickness, CV_AA);
    cv::line(image, points[1], points[2], color, thickness, CV_AA);
    cv::line(image, points[2], points[3], color, thickness, CV_AA);
    cv::line(image, points[3], points[0], color, thickness, CV_AA);
}
 

另附上TinyLA.cpp中的相關注釋：

bool isInto(cv::Mat &contour, std::vector<cv::Point2f> &b)
{
  for (size_t i=0;i<b.size();i++)
  {
      // 檢查指定的點和指定的多邊形的相對位置關係（在多邊形內、外、邊上或頂點上）
      // 返回值：該點和多邊形上最近的一條邊有符號的距離（>0表示在內部，<0表示在外部，=0表示在邊上）
      // 當最後一個引數值為0的時候，返回的距離只會是100或-100.
      if (cv::pointPolygonTest( contour,b[i],false)>0) return true;
  }
  return false;
}