That's all very well, but I need the design on the front, in order to stitch it. Now what?
To get the design from the back of the fabric onto the front, I stitched over the transferred design on the back with small running stitches:
Here, I've done the section on the right, to one side of the 'trilithon'. I've used a fairly dark blue sewing thread, so that later on it won't be seen.
This has the rather unfortunate side effect that it can't really be seen in my photographs, either.
I'm afraid photography isn't my strongest suit (I expect you've realised that!) and I've done my best, but it's not marvellous and it makes the green fabric look a nasty muddy colour that is not how it looks in real life at all. Anyway, if you peer at it as best you can, you should be able to see the design in a dotted line formed by the running stitches on the front fabric.
There's a brief overview of different methods of transferring a design to fabric here, but despite being by far the most time-consuming, this is definitely my favourite. It's great for getting a design onto dark fabric where other methods are hard to see, and, most importantly, it doesn't mark the top fabric at all. If I decide a line is in the wrong place I can just unpick the stitches and it's as though it was never there, while all other methods that mark up the top fabric can leave traces that can be very difficult to get rid of. It might take a while to do, but it's worth it.
Back to the design. I'm going to be building it up in stages, which should make sense as I go along. The first stage is the spirals in the top, blue, half outside of the trilithon. Once all the running stitches have been done over the design on the back, I have all the design for the part I'll be working on first transferred to the front:
Time to start proper stitching!