The module itself is basically just a helper module that sets up flightplan parameters during a polygon survey. Rather than manually figuring out the optimal solution for survey line spacing and altitude, it will calculate that for you based on some basic camera parameters. Some basic docs are here:
http://paparazzi.github.io/docs/v5.0/photogrammetry__calculator_8h.html (or in sw/airborne/modules/cartography/photogrammetry_calculator.c)
You can try it out in simulation pretty easily I think. Hope that helps.