It is a little curious when the vanishing points end up within the image area, the grid lines form solid gray blobs as the line width is constant. It makes sense if you look at the full size image as the grid lines then are more clearly visible. On another note, now I have totally caught up with myself, so from now on figures will be posted even more spaciously. Either one each month, or if I get overly creative (have time!), every other week.
If you travel with your mind clockwise around the center rectangle you will notice that you always go forward, out of the picture. If you split the figure vertically at the center you will always go backwards, into the image, if you follow any of the sides in a clockwise direction.