PFL's
Mike Cross is exactly right, the method is called the "constant aspect " and you keep your landing point in the same place in the window (be it the side window in a gentle spiral or the windscreen during a straight in.
You dont need to know aircraft glide performance (with the exception of the correct speed/pitch) or have to worry about a height to be at at any given point.
It works a dream and I've taught it at PPL level for 3 yrs now ever since I was converted to it on my instructors course.
LP