Thread: The geometry of Gothic tracery

I have no idea if this is the best place to put this, but, I am trying to find a source that will allow me to understand the maths/geometry behind the tracery seen in Gothic church furniture. I have a book containing the plates from the Brandons' treatise on Gothic architecture.

Attachment 392376

As you can see from the sketch the centres of the arcs are shown. The problem is without knowing how those centres were constructed it is dificult to do anything other than copy the ornamentation. Similarly there is no indication on the construction of the various trefoil details within the created shapes I would like to be able to create all these details from scratch.
Any ideas?
Philip.