Hello Varga Csaba,
sorry for this very late reply...but it is a busy period for me :-S
I wrote this code in jython, essentially it permits to the user to draw the five points in clockwise
and the with some check of the user like adjust lines, adjust points and so
it finds the diagonals and calculates the Xi point!
This is a very naive implementation, to be more like you want we have to add some listener to draw points perpinduclar and so on.
If you like it (I've attached you as .py file you can launch it by script editor selecting Python Language) we can try to improve a little and ok by the way export some parameters of your interest.. like distances angles between points and lines.
Have a nice day,
cephalometric_analyzer.zip (2.3 KB)