[fitswcs] Paper 1 comment

[William Pence]

After reading the 15 Jan 2002 version of the the first WCS Paper, I have a
couple questions:

1.  The paragraph describing the 'bracket' convention for specifying the
units of a keyword value in the comment field of the keyword (e.g., FREQ =
1.42E+09 / [Hz]) seems to have been removed.  I don't object to this, but
just wanted to make sure this was intentional.  I'm assuming that this was
removed from the WCS paper because a separate proposal to modify the FITS
Standard to recognize this units convention is now pending before the North
American FITS committee.

2.  At the end of section 3.3 "Keyword naming convention", a new paragraph
has been added which describes how the Coordinate Parameters, PVj_ms, could
be written to a table column instead of storing them as keyword values (and
hence limited to at most only 9 parameters).   How does this work?  In the
Pixel List case, does this mean the table would contain columns named
'TPV1', 'TPV2', etc. to hold the parameter values (up to 99 of them)?  What
if the pixel list table contains millions of rows?  How does one tell how
many Parameter Values are in the column, and what value is written to the
column in all the higher numbered rows.  Note that these new columns could
significantly increase the size of the pixel list table.

In the BINTABLE vector case, the table may only contain a few rows, or even
just a single row, where each row contains an image in a vector column.   Is
it assumed that all the images (rows) in the table use the same non-linear
projection algorithm, and all have the same values for the coordinate
parameters.  If that table only has a single row, how can up to 99
parameters be written to the table?

Bill Pence
-- 
____________________________________________________________________
Dr. William Pence                          pence at tetra.gsfc.nasa.gov
NASA/GSFC Code 662         HEASARC         +1-301-286-4599 (voice)     
Greenbelt MD 20771                         +1-301-286-1684 (fax)