code: public long getId(double x, double y) {
  		double down = (extentMax - y) / binSize;
  		double over = (x - extentMin) / binSize;
  		
  		return ((long)down * numCols) + (long)over;
  	}
docs: Gets bin ID from a point.
  
  @param x
  @param y
  @return