BASIC SPIRAL This is a way to make a pure geometric spiral in which r = a + bTheta. (Known as concentric or Archimedean).
There are easier ways to make an 'apparent' spiral such as using linked half-circles; this method is used in most crop circle 'spiral' formations, but they are not true spirals.
This shows the effect of using 4, 3 or 2 sticks to make the "virtual wheel". In all cases the 'spiral' is actually a series of linked part-circles. The more sticks used, the closer to a pure spiral such as would be obtained using a real wheel. But even 3 sticks gives a good curve which would be hard or impossible to distinguish from aerial photos.