UCD for SIAP

[Roy Williams]

One of my actions as part of the UCD steering committee is to work with the
"VOX" new UCDs that were created for the SIAP protocol.

Below, I have listed all of the VOX UCDs that could find in the SIAP
definition, with a little bit of the description. I have tried to find an
equivalent in the standard UCD set, and in many cases was successful. For
example is there a reason for VOX:Image_AccessReference as a new UCD, why
can't we simply use DATA_LINK from the existing set? This is why it says
"**existing: DATA_LINK" for that entry.

Of course, there will a revision when we steel on the "base+modifier" scheme
for UCD that we decided in Cambridge.

Please can some of you look at the suggested equivalents fron the exisiting
set, and the suggested new UCDs in the listing below? We gain
interoperability from reusing and following the existing tree -- but do we
lose anything?

Thenk You
Roy

--------
Caltech Center for Advanced Computing Research
roy at cacr.caltech.edu
626 395 3670

VOX:Image_Title
** existing: ID_IMAGE
containing a short (usually one line) description of the image.

VOX:Image_MJDateObs
** existing: TIME_DATE
with datatype="double", representing the mean modified Julian date of the
observation.

VOX:Image_Naxes
** new: POS_TRANSF_WCS_NAXES
specifying the number of image axes.

VOX:Image_Naxis
** new: POS_TRANSF_WCS_NAXIS
NOTE: Can a UCD refer to an array like this?
with the array value giving the length in pixels of each image axis.

VOX:Image_Scale
** new: POS_TRANSF_WCS_CDELT
NOTE: Can a UCD refer to an array like this?
with the array value giving the scale in degrees per pixel of each image
axis.

VOX:Image_Format
** new: DATA_TYPE_MIME
specifying the MIME-type of the object associated with the image acref,
e.g.,  image/fits", "text/html", and so forth.

VOX:STC_CoordRefFrame
** existing: ID_FRAME
representing the coordinate system reference frame, selected from "ICRS",
"FK5", "FK4", "ECL", "GAL", and "SGAL".

VOX:STC_CoordEquinox
** existing: TIME_EQUINOX
representing the Equinox (not required for ICRS) of the coordinate system
used for the image world coordinate system (WCS).

VOX:WCS_CoordProjection
** new: POS_TRANSF_WCS_CTYPE
with the array value being the three-character code ("TAN", "ARC", "SIN",
etc.)

VOX:WCS_CoordRefPixel
** new: POS_TRANSF_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
** new: POS_TRANSF_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
** new: POS_TRANSF_WCS_CD
with the array (matrix) value specifying the WCS CD matrix.

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

VOX:BandPass_Unit
** existing: UNITS -- but should be GROUPED with Bandpass
identifying the units used to represent spectral values, selected from
"meters", "hertz", and "keV".

VOX:BandPass_RefValue
** new: INST_FILTER_REF
specifying the characteristic (reference) frequency, wavelength, or energy
for the bandpass model.

VOX:BandPass_HiLimit
** new: INST_FILTER_MAX
specifying the upper limit of the bandpass.

VOX:BandPass_LoLimit
** new: INST_FILTER_MIN
specifying the lower limit of the bandpass.

VOX:Image_PixFlags
** existing: CODE_MISC
specifying the type of processing done by the image service to produce an
output image pixel. The string value should be formed from some

combination of the following character codes: C, F, X, Z, V

VOX:Image_AccessReference
** existing: DATA_LINK
specifying the URL to be used to access or retrieve the image.

VOX:Image_AccessRefTTL
** existing: TIME_DELAY
specifying the minimum time to live in seconds of the access reference.

VOX:Image_FileSize
** new: DATA_SIZE
representing the actual or estimated size of the encoded image in bytes (not
pixels!).