[fitswcs] [Fwd: Re: WCS Paper III comments]

[Eric Greisen]

Dr. Osuna's suggestions seem to be a very clever and scientifically
useful approach to automate the handling of units.  However, I think
there are several essential objections to including them in Paper III.

1. The suggestions are incomplete since there are fundamental units
not described and since the suggestion is not fleshed out with an
adequate description.

2. The suggestions cover the matter of units which are described by a
section in Paper I not III and Paper I has already been adopted by the
IAU.  The units description in Paper I is a minor deviation from the
description traditionally used by the IAU, but, even so, I was amazed
to get agreement on it between the major data centers.  This is a very
difficult area with a long tradition.

3. I do not think that we should delay Paper III for the time
(it could, and perhaps should, take years) that it will require to get
full agreement on Dr. Osuna's suggestions.  Instead, I would encourage
the VO people to pursue a complete description of their proposal,
including FITS keywords, and then pursue agreement on them in both the
VO and FITS communities.  The FITS keywords should probably consist of
two words per axis rather than combining the two strings in one in
order to avoid parsing/interpretation difficulties.  Note that there
also needs to be similar keywords to cover the tradition BUNIT keyword
as well.

Eric Greisen