Lou Deeter is quite correct in his suggestion that the angles can be measured by trigonometry. Certainly the seat angle is the simpler of the two, but the head angle can be measured with a bit more fifling about.
Most French and possibly manufacturers never used to give the seat angle, but refer to it by a measurement of the set-back, in millimeters from a vertical line through the bottom bracket to the centre-line of the top-tube to an imaginary line running along the centre of the seat tube.
When I used to import Vitus Duralinox and TVT frames..that was all the information that I could get from the manufacturer. Obviously when the set-back angle is given in the catalogue or spec sheet its much easier than measuring it yourself.
Many jigs used by these manufacturers actually had their jigs callibrated in millimeters to enable the angles to be set very accurately.
Norris Lockley
Settle (where it has rained continuously all day. UK