code: public Point2D queryCorner(int index) {
  		switch (index) {
  		case 0:
  			return Point2D.construct(xmin, ymin);
  		case 1:
  			return Point2D.construct(xmin, ymax);
  		case 2:
  			return Point2D.construct(xmax, ymax);
  		case 3:
  			return Point2D.construct(xmax, ymin);
  		default:
  			throw new IndexOutOfBoundsException();
  
  		}
  	}
docs: Queries a corner of the envelope.
  
  @param index
  Indicates a corner of the envelope.
  <p>
  0 means lower left or (xmin, ymin)
  <p>
  1 means upper left or (xmin, ymax)
  <p>
  2 means upper right or (xmax, ymax)
  <p>
  3 means lower right or (xmax, ymin)
  @return Point at a corner of the envelope.