SED Data Model: Questions and Comments

[David Berry]

On Tuesday 15 February 2005 12:42 pm, Gilles DUVERT wrote:
> If 'Quantity' is, or will be, able to deal with such things as flux
> conversions from/to air wavelength vs. humidity and frequency,etc..  and
> Janskys from/to Cousins/Johnson magnitudes, at least to a large extent
> and great accuracy, all the best. In that case all units or combinaisons
> thereof supported by Quantity should be authorized in, e.g., the SED DM.
> But at the same time one could use the Quantity DM to convert the data
> beforehand to specific quantities that would be the only  ones referred
> to in the SED DM, such as basic  MKSA units. And make the DM simpler.

The issue is ensuring that the model includes all the necessary meta-data
needed to convert *from* MKSA units to other more esoteric systems. For
instance, if all flux density-like data is required to be stored in
W/m^2/Hz (or do I mean W/m^2/Angstrom?) within the DM but the end user
wants to see antenna temperature, then the DM needs to include all the
necessary efficiency factors, etc, needed to do this conversion. Likewise,
converting to/from magnitudes.

Then what if the meta data needed to convert from your estoteric system to
the standard DM system are only poorly known? It is surely possible that
useful science could be done in the esoteric system, without ever
converting to the standard system. But if the DM *insists* that all data
is converted to a standard system, then you are immediately introducing
errors which need not be there.

So what system should the DM use for flux density-like data?


David