New UCD1+ for SIA protocol

[Roy Williams]

Dear UCD and DAL folks

Three of us (Sebastian Derriere, Andrea Preite-Martinez, myself) have been
working on an update for the SIA protocol that uses the standard UCD set,
now called UCD1+, rather than the ad hoc namespace VOX that SIA 1.0 has been
using.

In the following, all UCD from the original SIA specification are listed
below. The old SIA UCD is written first, then the suggested new UCD1+ is
written in the line beginning "-->"

The UCD1+ is not fully documented yet, but you can find a dictionary from
UCD1 to UCD1+ at
http://vizier.u-strasbg.fr/UCD/lists/ucd1-ucd1p.txt
and
http://vizier.u-strasbg.fr/UCD/lists/ucd1p-composed.txt

The SIA protocol is defined at
http://us-vo.org/pubs/files/ACF8DE.pdf

The new SIA will be version 1.1, and we are hoping to draft and approve this
at the IVOA meeting at the end of May.

Thank you for your comments and suggestions on these new assignments
Andrea, Roy, Sebastian

--------------------------------------------------------

VOX:Image_Title
--> meta.title
containing a short (usually one line) description of the image. This should
concisely describe the image to a user, typically identifying the image
source (e.g., survey name), object name or field coordinates,
bandpass/filter, and so forth.

INST_ID
--> meta.id;instr
identifying the instrument or instruments used to make the observation,

VOX:Image_MJDateObs
--> time.epoch
representing the mean modified Julian date of the observation.

POS_EQ_RA_MAIN
--> pos.eq.ra
representing the ICRS right-ascension of the center of the image.

POS_EQ_DEC_MAIN
--> pos.eq.dec
representing the ICRS declination of the center of the image.

VOX:Image_Naxes
--> pos.wcs.naxes
specifying the number of image axes.

VOX:Image_Naxis
--> pos.wcs.naxis
with the array value giving the length in pixels of each image axis.

VOX:Image_Scale
--> instr.scale
with the array value giving the scale in degrees per pixel of each image
axis.

VOX:Image_Format
--> meta.code.mime
specifying the MIME-type of the object associated with the image acref,

VOX:STC_CoordRefFrame
--> pos.frame
representing the coordinate system reference frame, selected from "ICRS",
"FK5", "FK4", "ECL", "GAL", and "SGAL".

VOX:STC_CoordEquinox
--> time.equinox
representing the Equinox (not required for ICRS) of the coordinate system

VOX:WCS_CoordProjection
--> pos.wcs.ctype
the array value being the three-character code ("TAN", "ARC", "SIN", and so
forth) specifying the celestial projection

VOX:WCS_CoordRefPixel
--> pos.wcs.crpix
with the array value specifying the image pixel coordinates of the WCS
reference pixel. This is identical to "CRPIX" in FITS WCS.

VOX:WCS_CoordRefValue
--> pos.wcs.crval
with the array value specifying the world coordinates of the WCS reference
pixel. This is identical to "CRVAL" in FITS WCS.

VOX:WCS_CDMatrix
--> pos.wcs.cdmatrix
with the array (matrix) value specifying the WCS CD matrix. This is
identical to the "CD" term in FITS WCS, and defines the scale and rotation
(among other things) of the image.

VOX:BandPass_ID
--> instr.bandpass
identifying the bandpass by name (e.g., "V", "SDSS_U", "K", "K-Band", etc.).

VOX:BandPass_Unit
--> meta.unit
identifying the units used to represent spectral values, selected from
"meters", "hertz", and "keV".

VOX:BandPass_RefValue
--> em.wl OR em.freq OR em.energy
specifying the characteristic (reference) frequency, wavelength, or energy
for the bandpass model.

VOX:BandPass_HiLimit
--> em.wl;stat.max OR em.freq;stat.max OR em.energy;stat.max
specifying the upper limit of the bandpass.

VOX:BandPass_LoLimit
--> em.wl;stat.min OR em.freq;stat.min OR em.energy;stat.min
specifying the lower limit of the bandpass.

VOX:Image_PixFlags
 --> meta.code
specifying the type of processing done by the image service to produce an
output image pixel.

VOX:Image_AccessReference
--> meta.ref.url
specifying the URL to be used to access or retrieve the image.

VOX:Image_AccessRefTTL
--> time.interval;stat.min
specifying the minimum time to live in seconds of the access reference.

VOX:Image_FileSize
--> phys.size;meta.file
representing the actual or estimated size of the encoded image in bytes (not
pixels!).