Computing the Hough Transform

Listing 2: An accumulation function for line search.

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;
}