So I found an excellent youtube channel - Mohamad Aljanabi - that gives exact construction methods for many of the patterns I have been drawing. He is very dismissive of the ‘grid’ (or ‘Western’) method that some (apparently) use, as it results in distortions of the geometry. Thankfully I’ve mostly avoided this terrible mistake! … Although I have used the book by Keith Critchlow (‘Islamic Patterns’) that he specifically calls out. Oops.
Anyway, the constructions methods are … very thorough. Some of the patterns require more than 20-30 construction elements (lines and circles) before you can draw the pattern.
So I decided to make a ‘study’ of the construction lines for a simple four-fold pattern in a rectangle. Then draw the same but with the pattern on top, then finally just the pattern:
Fairly simple, but came out quite nice, I think. One minor detail is that the gap between rectangles is 12 mm; the same as the circle radius in the lower right and upper left. Not sure that matters, but still.
Here is the link to the finished item on Etsy