TG: That was a stock photo of a drawing I did for one of my workshop frames.
When I print a 2d drawing of a joint I like to add a 3d view to show the student what the whole thing will look like.
NH: I understand your point. But this frame has several "general frame rules", and one rule is that the layout of tenons and their mortises are 2" off the reference face and then 2" thick/wide. So with this cross sill (the one with the tenon) connecting to the long sill (the one with the mortise and floor joist drop in pockets) joint, this rule has been met.
Another rule for this frame is that all joints are reduced to the next 1/2" smaller in size (of the actual timber). This is shown by the reduction of the tenon on the inside of the frame.
These two rules are just some of the rules we use when doing square rule joinery, on non planed timbers.
(I'm just posting this as some general info for others not familiar with square rule joinery).

Jim Rogers