[h5md-user] units module

[Peter Colberg]

Hi,

Before adding a units module to the repository that defines an
optional unit system for the "unit" attributes, I would like to
solicit feedback from the H5MD community.

The idea is to have a module named "units" that carries a module
attribute "system" that defines the unit system. Rather than having
a separate module for each unit system, this way a program can query
the unit system by reading the attribute "/h5md/modules/address@hidden".

The module would initially support the unit system "si". Here the
question is whether and how to define the format of the unit strings.
Konrad suggested the udunits2 package earlier. It seems a good basis:

http://www.unidata.ucar.edu/software/udunits/udunits-2/udunits2lib.html#Syntax

The udunits2 grammar is very flexible. It would probably be sensible
to define a smaller grammar, so programs wishing to interpret units do
not have to use the udunits2 library due to the complexity of parsing.

Debian ships with a udunits-bin package if you wish to try the syntax.

Peter