Computing the Hough Transform
by Andrew Queisser


Listing 1
for (double theta=0.0, thetaIndex=0; 
      theta<PI; 
      thetaIndex++, theta+=PI/numAngleCells)
{
  rho = rhoMax + x*cos(theta) + y*sin(theta);
  accum[thetaIndex][(int)rho]++;
}


Listing 2
bool LineHoughAccum::DoAddPoint(int x, int y)
{
  int a;
  int distCenter = m_rowLength/2;
  // calculate rho for angle 0
  int lastDist = distCenter + ((m_cosTable[0]*x + m_sinTable[0]*y) >> 10);
  // loop through angles 1 through 180
  for (a=1; a<m_cosTable.size(); a++)
  {
    int dist = distCenter + ((m_cosTable[a]*x + m_sinTable[a]*y) >> 10);
    if (dist >= 0 && dist<m_rowLength)
    {
      // accumulate cells filling in multiple values for one angle
      int stepDir = dist>lastDist ? 1 : -1;
      for (int cell=lastDist; cell!=dist; cell+=stepDir)
        m_accum[a*m_rowLength + cell] += 1;
    }
    lastDist = dist;
  }
  m_numAccumulated += 1;
  return true;
}


Listing 3
x -= dx/2;   y -= dy/2;
for (thetaIndex=0; thetaIndex<cosTable.size(); thetaIndex++)  
{
  rho = rhoMax + x*cosTable[thetaIndex] + y*sinTable[thetaIndex];
  rho >>= 1; // represents a rhoDivisor of 2
  accum[thetaIndex][(int)rho]++;
}


Listing 4
class HoughAccum
{
protected:
  int m_dx, m_dy;
  vector<int> m_accum;
  int m_rowLength;
  int m_numAccumulated;
  virtual bool DoAddPoint(int x, int y)=0;
public:
  HoughAccum();
  virtual ~HoughAccum();
  virtual void Init(int dx, int dy)=0;
  virtual void Clear();

  bool AddPoint(int x, int y);

  int GetCell(int row, int col) { return m_accum[row*m_rowLength + col]; }
  void SetCell(int row, int col, int value) { 
                                 m_accum[row*m_rowLength + col] = value; }
  void GetAccumSize(int *numRows, int *numCols) 
  { 
    *numRows = m_accum.size()/m_rowLength;
    *numCols  = m_rowLength;
  }
  int NumAccumulated() { return m_numAccumulated; }
};
class LineHoughAccum 
  : public HoughAccum
{
protected:
  vector<int> m_cosTable;
  vector<int> m_sinTable;
  virtual bool DoAddPoint(int x, int y);
public:
  LineHoughAccum(int numAngleCells);
  virtual ~LineHoughAccum();
  virtual void Init(int dx, int dy);
};






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