solar coordinate systems, VOEvent and the IVOA
Frank Hill
hill at noao.edu
Thu May 18 14:24:17 PDT 2006
Bill's comments are all good, but there is one more detail
-- depth below the photosphere, or height above it. For
me, and for the helioseismology crowd, that is Z. So,
Longitude, Latitude, and Depth might be an alternative
coordinate system.
F Hill
On Tue, 16 May 2006 16:05:00 -0400
William Thompson <William.T.Thompson.1 at gsfc.nasa.gov>
wrote:
> Dear VO community:
>
> When I wrote my paper, "Coordinate systems for solar
>image data", I tried to tie together existing usage
>within various members of the solar community, which
>don't always come from the same traditions. The question
>is raised whether there's a bifurcation between the solar
>and planetary communities. In my view, it's really of a
>bifurcation between imaging and non-imaging uses of
>coordinate systems.
>
> When one examines a 2D photograph of the Sun, it's
>common practice within the solar community to label the
>East-West axis as "X", and the North-South axis as "Y".
> These are really angles rather than distances, but
>they're often treated interchangeably. In my paper, I
>use the notation X and Y as an intermediate step, to
>connect my discussion to current practice within FITS
>files, but the ultimate axis labels refer to longitude
>and latitude rather than X, Y, or Z.
>
> I also reference F&H in my paper, and outline a
>methodology for specifying the viewing position within
>FITS headers. Those keywords use the standard coordinate
>systems used within the planetary community, all of which
>have Z along the axis of rotation. I also describe how
>the intermediate heliocentric-cartesian coordinates of my
>paper are related to the standard
>Radial-Tangential-Normal (RTN) coordinates used within
>the planetary community, which is just a notational
>difference.
>
> I think the proper course to take is quite clear.
> Positional information should always be given in
>standard coordinates as described in F&H, such as HEE,
>HEEQ, etc. Directional vectors (e.g. solar wind
>velocity) would also be given in these coordinate
>systems, or in a spacecraft-centered coordinate system
>such as RTN (also described in F&H). All of these have Z
>along the axis of rotation.
>
> Angular directional information, such as in images,
>should be given as longitude and latitude. My paper
>defines two different angular coordinate systems,
>helioprojective-cartesian (HPLN/HPLT) and
>helioprojective-radial (HRLN/HRLT), as well as
>heliographic coordinates (HGLN/HGLT, CRLN/CRLT). This is
>the purpose of my paper--I never intended that the
>intermediate heliocentric coordinates I describe supplant
>the standard heliospheric coordinate systems such as RTN.
>
> Within the STEREO project, we're using
>helioprojective-cartesian coordinates for the solar
>images, and the F&H coordinate systems (including RTN)
>for orbital position and solar wind measurements.
>
> Bill Thompson
>
>
> Joseph B. Gurman wrote:
>> Bill -
>>
>> Comments?
>>
>> Thanks,
>>
>> Joe
>>
>>> X-Sieve: CMU Sieve 2.2
>>> Date: Thu, 11 May 2006 17:32:59 +0100 (BST)
>>> From: Elizabeth Auden <eca at mssl.ucl.ac.uk>
>>> To: hill at noao.edu, gurman at gsfc.nasa.gov,
>>>hurlburt at lmsal.comm
>>> Subject: solar coordinate systems, VOEvent and the IVOA
>>>
>>> Hi guys,
>>>
>>> I received this message from the IVOA VOEvent mailing
>>>list. Arnold
>>> Rots is asking about the solar community's preference
>>>for coordinate
>>> systems - do you have any comments to the message below?
>>>You can reply
>>> directly to the VOEvent mailing list (voevent at ivoa.net)
>>>or to me if
>>> you like. I believe there will be at least one session
>>>discussing the
>>> VOEvent schema at the IVOA interoperability meeting in
>>>Canada next
>>> week (unfortunately, I'm not going, but Silvia Dalla
>>>will be
>>> championing the solar cause).
>>>
>>> Thanks for your comments, and I hope you're having a
>>>great time in
>>> Sicily if you're at SOHO-17 this week.
>>>
>>> cheers,
>>> Elizabeth
>>>
>>> --
>>> Elizabeth Auden, MSSL
>>> Holmbury St. Mary, Dorking RH5 6NT
>>> Tel: +44 (0)1483 204 276
>>> eSDO Technical Lead, AstroGrid Developer
>>>
>>> ---------- Forwarded message ----------
>>> Date: Thu, 11 May 2006 12:03:47 -0400 (EDT)
>>> From: Arnold Rots <arots at head.cfa.harvard.edu>
>>> To: Elizabeth Auden <eca at mssl.ucl.ac.uk>
>>> Cc: Rob Seaman <seaman at noao.edu>, IVOA List VOEvent
>>><voevent at ivoa.net>
>>> Subject: Re: VOEvent 1.1 new draft with STC elaboration
>>>
>>> I have been talking with Ed DeLuca here, who is working
>>>on Solar-B,
>>> and this has exposed some problems that should be
>>>addressed soon.
>>> The solar coordinate systems in STC were largely based
>>>on Fraenz &
>>> Harper, including some of the Hapgood systems: HEE,
>>>HEEQ, HCI, and
>>> HCD, in addition to a generic Heliographic.
>>> But then there is Bill Thompson's FITS WCS paper on
>>>solar coordinate
>>> systems which, in general, tends to put the z axis along
>>>the
>>> observer-sun line (as opposed to the x axis in F&H). It
>>>also became
>>> clear that helioprojective coordinates may need to be
>>>represented.
>>>
>>> I'd like the solar community to tell us whether there is
>>>a consensus:
>>> should I go with the Thompson systems? are these the
>>>ones that are
>>> most commonly used?
>>> Or are we seeing here a bifurcation between solar and
>>>planetary types,
>>> with the former's customs represented by Thompson, the
>>>latter's by F&H?
>>> What coordinate frames would solar and planetary people
>>>really like to
>>> see?
>>>
>>>
>>> Thanks,
>>>
>>> - Arnold
>>>
>>>
>>> Elizabeth Auden wrote:
>>>
>>>>>> Elizabeth Auden (MSSL/AstroGrid) and myself have an
>>>>>>interest in
>>>>>> VOEvent
>>>>>> applied to solar events. I will be at the IVOA interop
>>>>>>meeting next
>>>>>> week.
>>>>>
>>>>>
>>>>> And Frank Hill spoke on solar transients at VOEvent II
>>>>>(http://
>>>>> www.ivoa.net/twiki/bin/view/IVOA/VoeventWorkshop2).
>>>>
>>>>
>>>> I followed up with Frank Hill and Neal Hurlburt about
>>>>solar VOEvents
>>>> this
>>>> past February at an SDO workshop. They're both
>>>>interested in developing
>>>> solar VOEvents as well, and Neal in particular is
>>>>working on a VOEvent
>>>> packet for Solar-B data.
>>>>
>>>> Elizabeth
>>>>
>>>> --
>>>> Elizabeth Auden, MSSL
>>>> Holmbury St. Mary, Dorking RH5 6NT
>>>> Tel: +44 (0)1483 204 276
>>>> eSDO Technical Lead, AstroGrid Developer
>>>>
>>> --------------------------------------------------------------------------
>>>
>>> Arnold H. Rots Chandra
>>>X-ray Science
>>> Center
>>> Smithsonian Astrophysical Observatory
>>> tel: +1 617 496
>>> 7701
>>> 60 Garden Street, MS 67
>>> fax: +1 617 495
>>> 7356
>>> Cambridge, MA 02138
>>> arots at head.cfa.harvard.edu
>>> USA
>>> http://hea-www.harvard.edu/~arots/
>>> --------------------------------------------------------------------------
>>>
>>
>>
>>
>
> --
> William Thompson
> NASA Goddard Space Flight Center
> Code 612.1
> Greenbelt, MD 20771
> USA
>
> 301-286-2040
> William.T.Thompson.1 at gsfc.nasa.gov
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