Dear Ferret users and developers,
I was wondering how the modulo=0 setting is interpreted by Ferret and how common this convention is.
I tried to look up how modulo is defined in the CF convention and was a bit surprised that it's not included in it. (Please correct me if I'm wrong.) It seems to have been discussed for a long time without reaching a consensus:
In this context, I'm interested that when modulo is specified without a value, like so
define axis/t0=1-JAN-0001/calendar=noleap/edges/t=0:365/npoints=73\
/units=days/MODULO pntd
Ferret saves this axis into a netCDF file with
PNTD:modulo = 0.f ;
The above time axis has gridpoints at t = 2.5, 7.5, . . . , 362.5 . Does this mean that
1) the span + Δt is taken as the modulo value? If so,
modulo = 362.5 - 2.5 + 5 = 365.
2) the calendar year is taken as the modulo value? In this case also modulo = 365.
Which is the case? For the above particular case, the result is the same, but for other axes, the results will be different.
Also, is modulo=0 a widely used convention? or is it only Ferret?
Best regards,
Ryo