code: public void queryEnvelope(long binId, Envelope envelope) {
  		long down = binId / numCols;
  		long over = binId % numCols;
  		
  		double xmin = extentMin + (over * binSize);
  		double xmax = xmin + binSize;
  		double ymax = extentMax - (down * binSize);
  		double ymin = ymax - binSize;
  		
  		envelope.setCoords(xmin, ymin, xmax, ymax);
  	}
docs: Gets the envelope for the bin ID.
  
  @param binId
  @param envelope