Yup, I was at Robert's talk and demonstration. Very cool stuff.
Ferd, it's really a very specific joint for pretty specific situations. It's technically a mitered joint, but only for logs with the same diameter (as Robert pointed out). You can miter logs with different diameters, but you end up having to fair them out at the joint, because they will never meet perfectly. What Robert realized by looking at some obscure geometry is that they do perfectly meet when the diameters are the same. The result is a really clean joint, that also can include some internal joinery.
He presented a few methods of executing the joint. The standard way would be with lofting, but there are some disadvantages to that. The method he is showing is basically using a template. I'd have to review my notes to try to explain it, and it's not something that is very explainable in words alone. I don't think that he's measuring in those photos, but rather bringing a point up from the template.
I can try to answer more specific questions, but most of this sort of thing is hard to explain. I would definitely check out Will's articles that he mentioned. And the ILBA has a book on cutting with jigs that goes over a bunch of different approaches.
