[fitsbits] FITS standard for spatial planetary data

[William Thompson]

On 08/27/15 13:57, Steve Allen wrote:
> On Thu 2015-08-27T19:33:15 +0200, Chiara Marmo hath writ:
>> I am a Research Engineer in a French lab involved in Planetary Sciences (surface imagery and spectro-imagery, in particular).
>>
>> As part of the Europlanet H2020 project we want to propose standard FITS keywords for planetary surface observations.
>
>> 1) A working group on Planetary Data already exists?
>
> My immediate impression is that the WCS needs of this project should
> share some of the conventions that have been needed by the solar
> astronomy community for describing the observations of features on the
> solar surface.

I guess I should chime in at this point, since I'm the one who worked on the 
adoption of WCS to solar coordinates.  This is outlined in the paper

http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006SPD....37.0307T&db_key=AST&link_type=ABSTRACT&high=48bdb5fcba04631

and there are a couple of follow-up papers:

http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010SoPh..261..215T&db_key=AST&link_type=ABSTRACT&high=48bdb5fcba04631

http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010A%26A...515A..59T&db_key=AST&link_type=ABSTRACT&high=48bdb5fcba04631

There's always been a well-defined coordinate system for describing the 
locations of features on the solar photospheric surface, known as Carrington 
longitude and latitude.  Related to that are Stonyhurst coordinates that are 
typically used for describing the instantaneous positions of flares and other 
transient phenomena.  The only innovation that I added to these was to 
explicitly define Stonyhurst coordinates as being based on the view from Earth. 
  I know that the IAU defines similar planetocentric/planetographic coordinate 
systems for all the major planets in the solar system, even those like Jupiter 
which don't have a hard surface (like the Sun).

Less well defined were coordinate systems for images of the Sun.  It was common 
practice to use a cartesian-like system with the origin at the apparent center 
of the Sun in the image, with the "y" axis aligned with the projection of the 
solar north axis onto the image plane, and with the "x" axis pointed to the 
right, usually expressed in arcseconds.  My contribution was to firm this up so 
that the "x" axis was treated as a longitude, and the "y" axis was treated as a 
latitude.  This allowed the image coordinates to be extended out to any distance 
from the Sun.

I can't comment on what common practice is for planetary images.

>> 2) If not, is someone in this list interested in following or contributing to this discussion?
>
> Announcements always belong in fitsbits, and I think the initial
> coordination can also occur on fitsbits.
>
> To the extent that the planetary discussion delves into world
> coordinates that would fit well into the FITS WCS list
> fitswcs at listmgr.nrao.edu
>
>> 3) Once a draft of a document is ready, to whom do I submit it?
>> What is the procedure for the IAU evaluates and accepts the new
>> definitions?

For the solar coordinate system that I put together, it was decided that this 
constitutes a convention rather than a standard, so the IAU FITS committee did 
not vote on it as part of the standard.  However, before submitting it to the 
journal, I widely distributed drafts of the convention as it was being developed 
both to fitsbits and to the solarnews mailing list to solicit comments and 
community approval.

> The IAU reorganization that is currently in progress means that the
> answer that has been true may not be true by the time that a new
> document is ready, so (not to be too facetious) the Magic 8-Ball says
> "Ask again later".
>
> --
> Steve Allen                 <sla at ucolick.org>               WGS-84 (GPS)
> UCO/Lick Observatory--ISB   Natural Sciences II, Room 165   Lat  +36.99855
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-- 
William Thompson
NASA Goddard Space Flight Center
Code 671
Greenbelt, MD  20771
USA

301-286-2040
William.T.Thompson at nasa.gov