Raccord Roof Surface Miter Line

I was hoping for a lot more geometric development from the book L'art du Trait de Charpenterie, by Frères Billon. However, he does show an easy way to develop the miter line for the jack rafters and purlin rafters on the roof surface. Most of his drawings are Raccord drawings of the roof surface. Origami representation of the timbers fully developed on the roof surface joined together at the hip rafter, valley rafter or ridge line. It's more of an art technique by the French, then a practical way of developing the rafters on the roof surface. 

Anyway, here's the French technique of developing the line on the roof surface parallel to the hip rafter on the roof surface drawing  for the miter line of the jack rafters and purlin rafters. You would lay the jack rafter or purlin rafter on the Raccord drawing of the roof surface and transfer the miter lines to the rafter. The one thing that's missing from this technique are the lines on the roof surface for the claws/barbe's on the jack rafter or purlin rafter.