code: public void queryCorners(Point2D[] corners) {
  		if ((corners == null) || (corners.length < 4))
  			throw new IllegalArgumentException();
  		if (corners[0] != null)
  			corners[0].setCoords(xmin, ymin);
  		else
  			corners[0] = new Point2D(xmin, ymin);
  
  		if (corners[1] != null)
  			corners[1].setCoords(xmin, ymax);
  		else
  			corners[1] = new Point2D(xmin, ymax);
  
  		if (corners[2] != null)
  			corners[2].setCoords(xmax, ymax);
  		else
  			corners[2] = new Point2D(xmax, ymax);
  
  		if (corners[3] != null)
  			corners[3].setCoords(xmax, ymin);
  		else
  			corners[3] = new Point2D(xmax, ymin);
  	}
docs: Queries corners into a given array. The array length must be at least
  4. Starts from the lower left corner and goes clockwise.
  @param corners The array of four points.