That's the idea SteveJG!. Perfect. I was thinking in this kind of grid, also, we COULD use (my old idea of StereoNET) like a Wulff Net, equi angular or... MAYBE is more suitable for this kind of project --> the schmidt net (equi AREAL)!, because is EQUI AREAL, you can measure AREAS.
Anyway. I was thinking for this project an overlapping transparent png in the camera section and take only what is in the circular shape. So the area inside the circle could be easily measure.