OGF and negative values

[ricolab]

HI
First , i really like this project and i would like to use it on standard CNC not for PCBs.
Generate PFG works well , import RPF also (need to use the fixer but why not...).
My question is why you don't manage OGF with only positive values????
I use freecad to create 3D objects and to generate Gcode following Mach3 pattern.
Maybe i don't know how to have Z0 on top surface and negative value to cut
BUT it looks more simple to understand when 0 is the martyr surface and Positive Z are the piece points. If you go to Z0 , you want to totally cut. logical. No?
I am developper and i don't understand where the problem is (probably i don't have all the elements). You "just" have to apply correction from RPF matrix without changing sign.
Maybe a simple cursor to define orientation of the project before loading or beside Autoleveler button ???
Thanks