It's similar to the techniques in Eleanor Burns' Double Pinwheels and also Debbie Caffreys "Open a Can of Worms" and her other books. (Those are pretty old books - I don't know if they are in print anymore)
I took a class from Debbie Caffrey at a Quilt Market several years ago, and she provided the Ominigrid 96 and 96L and the 98 and 98L rulers that make those triangular cuts. They are REALLY good for that. I have used those rulers for several different projects since then, including the setting triangles for many "on point" things.
The rulers are a little hard to find, but they are worth the effort!