wow, it seems you have turned FlightGear into a plotting application meanwhile
Regarding the docs, I would suggest not to write any unless you have done some benchmarking and are satisfied with the performance ?
The point being that during the development of the fgplot tool, there were some performance issues that needed to be ironed out first.
Thus, I would not write/update any docs unless you are sure that the code will remain "as is" ?
For benchmarking purposes, it might be best to do some aggressive plotting - either using a handful of different graphs, or different functions plotted to the same graph.
As a matter of fact, most of the original fgplot topic was really all about potential performance improvements.
By the way, your plotProperty helper would be easy to reuse for a UI-driven mode where the property can be made user-configurable using a Canvas LineInput: http://wiki.flightgear.org/Canvas_Snipp ... put_Dialog
That would mean that you could more easily change/reconfigure the property to be used for the x/y axis (e.g. by clickign the axis/label)
I still have to look at your other changes to make any helpful comments - other than that, it seems that you have meanwhile definitely outgrown the original atc/gca purpose - so you may just as well ask one of the fgdata committers to commit your modules and/or move your helpers to a separate "plotting" addon, because none of this is specific to the atc/gca use-case anymore (if that is something you'd like to do, it might be a good idea to look at some of the original fgplot discussions/features to see what this was originally all about, I think it was primarily used for plotting fdm/autopilot properties...)
Again, I still have to look at your other changes to really understand what else you have changed there - but I think it's pretty safe to say that you have literally created a new API that could be used for developing all sorts of new features.