I am programming this in Procesing see my current code on Github

See the article in the Gardian which is inspiring me to draw this.

I have placed the code for this online at https://github.com/rupertrussell/Islamic_002

When I first started to program this I thought I need to be able to locate the x,y point of a projected line.

I am making progress I have finished drawing the centeral cross.

Finished it !

As it turnend out I decided to locate the intercetion points by hand which has workd out OK.

It turns out that I did not need to use The dot product metod to project the guidelines

I just used a larger outer circle that intersects with the boundary square and I then calculated

the 8 points on the circle where it intersects with the boundary

http://www.sunshine2k.de/coding/java/PointOnLine/PointOnLine.html#step5

5. What are the coordinates of the projected point on a line segment using the perp dot product ?

Vector Projections - Example 1