[fitsbits] Coordinate systems for solar image data (fwd)

PS:
This issue reminded me that there is still something lacking in WCS.
For geocentric equatorial coordinates we have RADESYS to tell us what
our coordinate reference frame is, but for all others we have to infer
it from the name of the individual coordinates.
It would have been convenient to have a single keyword that specifies
the spatial reference frame in use, and that could say 'FK4', 'ICRS',
'HCI', 'MAG', 'HCD', etc.
Then it would also be easy to add planetocentric coordinates, and we
could allow generic CTYPEs like X, Y, Z, LONG, LAT, etc.
What I'm saying is that extending the current standard is laborious
and could have been made easier.

- Arnold

----- Forwarded message from Arnold Rots -----


There are two other coordinate systems that have been suggested in the
context of the VO: HGC and HCD. I can't judge whether they are useful.

But I would suggest dropping GEI and HAE since, if I understand it
correctly, they are synonyms for ICRS and Ecliptic, respectively.

Cheers,

- Arnold

William Thompson wrote:
There's a new update of the paper Coordinate Systems for Solar Image Data
available at

http://orpheus.nascom.nasa.gov/~thom...oordinates.pdf

I've tried to take all of your user comments into account. Let me know if I
missed anything.

The major changes from the May 13th version a

1. Corrected the usage of i and j to match the final WCS paper usage.

2. Corrected Table 1, in particular the keyword "iVn_m"

3. Added a section on the use of cylindrical projections for synoptic maps.

4. Added heliocentric inertial (HCI) from Franz and Harper to Table 4.

Thank you to the people who've reviewed it so far for all your help.

William Thompson

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fitsbits mailing list

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--------------------------------------------------------------------------
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
USA http://hea-www.harvard.edu/~arots/
--------------------------------------------------------------------------

_______________________________________________
fitsbits mailing list

http://listmgr.cv.nrao.edu/mailman/listinfo/fitsbits

----- End of forwarded message from Arnold Rots -----
--------------------------------------------------------------------------
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
USA http://hea-www.harvard.edu/~arots/
--------------------------------------------------------------------------

PS:
This issue reminded me that there is still something lacking in WCS.
For geocentric equatorial coordinates we have RADESYS to tell us what
our coordinate reference frame is, but for all others we have to infer
it from the name of the individual coordinates.
It would have been convenient to have a single keyword that specifies
the spatial reference frame in use, and that could say 'FK4', 'ICRS',
'HCI', 'MAG', 'HCD', etc.
Then it would also be easy to add planetocentric coordinates, and we
could allow generic CTYPEs like X, Y, Z, LONG, LAT, etc.
What I'm saying is that extending the current standard is laborious
and could have been made easier.

- Arnold

----- Forwarded message from Arnold Rots -----


There are two other coordinate systems that have been suggested in the
context of the VO: HGC and HCD. I can't judge whether they are useful.

But I would suggest dropping GEI and HAE since, if I understand it
correctly, they are synonyms for ICRS and Ecliptic, respectively.

Cheers,

- Arnold

William Thompson wrote:
There's a new update of the paper Coordinate Systems for Solar Image Data
available at

http://orpheus.nascom.nasa.gov/~thom...oordinates.pdf

I've tried to take all of your user comments into account. Let me know if I
missed anything.

The major changes from the May 13th version a

1. Corrected the usage of i and j to match the final WCS paper usage.

2. Corrected Table 1, in particular the keyword "iVn_m"

3. Added a section on the use of cylindrical projections for synoptic maps.

4. Added heliocentric inertial (HCI) from Franz and Harper to Table 4.

Thank you to the people who've reviewed it so far for all your help.

William Thompson

_______________________________________________
fitsbits mailing list

http://listmgr.cv.nrao.edu/mailman/listinfo/fitsbits

--------------------------------------------------------------------------
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
USA http://hea-www.harvard.edu/~arots/
--------------------------------------------------------------------------

_______________________________________________
fitsbits mailing list

http://listmgr.cv.nrao.edu/mailman/listinfo/fitsbits

----- End of forwarded message from Arnold Rots -----
--------------------------------------------------------------------------
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
USA http://hea-www.harvard.edu/~arots/
--------------------------------------------------------------------------

On Fri 2004-07-09T09:50:23 -0400, Arnold Rots hath writ:
It would have been convenient to have a single keyword that specifies
the spatial reference frame in use, and that could say 'FK4', 'ICRS',
'HCI', 'MAG', 'HCD', etc.

Then it would also be easy to add planetocentric coordinates, and we
could allow generic CTYPEs like X, Y, Z, LONG, LAT, etc.

Until such time as a fully machine-readable instance of such coordinates
is developed WCS currently provides enough string-valued keywords to
permit rather complete text-based documentation of the axes.

WCSNAMEa serves to name the overall coordinate system, and it might
be adapted to permit conventional values as above.

CTYPEia is being constrained to a 4-3 form for non-linear coordinates,
but with WCS III this is loosened by adding the CNAMEia keywords.

--
Steve Allen UCO/Lick Observatory Santa Cruz, CA 95064
Voice: +1 831 459 3046 http://www.ucolick.org/~sla
PGP: 1024/E46978C5 F6 78 D1 10 62 94 8F 2E 49 89 0E FE 26 B4 14 93

On Fri 2004-07-09T09:50:23 -0400, Arnold Rots hath writ:
It would have been convenient to have a single keyword that specifies
the spatial reference frame in use, and that could say 'FK4', 'ICRS',
'HCI', 'MAG', 'HCD', etc.

Then it would also be easy to add planetocentric coordinates, and we
could allow generic CTYPEs like X, Y, Z, LONG, LAT, etc.

Until such time as a fully machine-readable instance of such coordinates
is developed WCS currently provides enough string-valued keywords to
permit rather complete text-based documentation of the axes.

WCSNAMEa serves to name the overall coordinate system, and it might
be adapted to permit conventional values as above.

CTYPEia is being constrained to a 4-3 form for non-linear coordinates,
but with WCS III this is loosened by adding the CNAMEia keywords.

--
Steve Allen UCO/Lick Observatory Santa Cruz, CA 95064
Voice: +1 831 459 3046 http://www.ucolick.org/~sla
PGP: 1024/E46978C5 F6 78 D1 10 62 94 8F 2E 49 89 0E FE 26 B4 14 93