We join round timbers quite often and it usually involves scribing with one piece set over another, then working off snap lines to level the pieces. A bubble scriber or laser level is used for round to round pieces or round to flat. For a description of the process. see issue #78 of Timber Framing or see the Timber Framing Fundamentals for the three-part scribing series I wrote. Both publications can be bought through the Guild store.
The Burlington process shown in photos indeed used a template and ground plane drawing. This was a radically new process developed by Rob Chambers because it allows you to join timbers of the same diameter (there's a mortise and tenon inside that joint). Previously one timber had to be at least two inches smaller in diameter to the other in order for the joint to look fluid.
