Ron, the AOA is defined as the angle between the wing chord line and the airflow at that point. So you have to be actually flying to measure it. What you are referring to is the old 'Riggers angle of
Incidence' or 'Wing to body angle'. This is simply the rigged angle of the wing to the fuselage and will dictate what angle the fuselage will ride at during straight and level flight. All these angles use the chord line of whatever section you use as the reference line. You can forget the bottom of the airfoil for any meaningful measurements. As you know the Chord line joins the centre of the leading edge radius to the centre of the trailing edge, and will be the longest straight line you can fit through the section.
Evan, WB#12.