[Fwd: Re: Fwd: solar coordinate systems, VOEvent and the IVOA]
William Thompson
William.T.Thompson.1 at gsfc.nasa.gov
Thu May 18 09:31:25 PDT 2006
I'm told that the following message has already been posted for me on this
newsgroup, but since I don't see it in the archives, I'm posting it again.
-------- Original Message --------
Subject: Re: Fwd: solar coordinate systems, VOEvent and the IVOA
Date: Tue, 16 May 2006 16:05:00 -0400
From: William Thompson <William.T.Thompson.1 at gsfc.nasa.gov>
To: Joseph B. Gurman <gurman at gsfc.nasa.gov>, voevent at ivoa.net
CC: thompson at lssp-mail.gsfc.nasa.gov, Sam Freeland <freeland at sxt1.lmsal.com>,
Elizabeth Auden <eca at mssl.ucl.ac.uk>, hill at noao.edu, hurlburt at lmsal.comm,
Arnold Rots <arots at head.cfa.harvard.edu>, Rob Seaman <seaman at noao.edu>,
edeluca at cfa.harvard.edu
References: <p06230908c089e91b204d@[192.168.1.197]>
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
--
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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