Subject: Re: wcs.ps

From: Arnold Rots <arots at head-cfa.harvard.edu>
Date: Thu, 1 Apr 1999 10:10:09 -0500 (EST)

Eric,

A few more comments on the WCS paper.

Units:
When we introduced the ADU for Chandra/AXAF files, last year, it was
decided to use the string "adu", in lower case.  Since that has been
written into a lot of software already, it would be helpful - to us,
at least - if you could also define that string as lower case.

I noticed that your list was missing the unit that is dear to many HEA
types' hearts: the "Crab".  Even though it's listed in the Chandra
FITS guide, I'm not sure I'd really want to argue for its inclusion in
your list. ;-)

Coordinates in binary tables:
I think it would be good to split the BINARY vector column in Table 7
also into new and old, where old is the convention that HEASARC
adopted a number of years ago and that got incorporated into the RXTE
archive: jCTYPn, jCUNIn, jCRVLn, jCRPXn, jCDLTn.  I know, that makes
it hard to fit into one text column, but ...
My recollection was that the old Pixel List increment was TCDLTn, not
TCDELn.
I would suggest changing the Vector increment keyword, in view of
these older forms, to jCDLns, rather than jCDEns.
In general, I would argue for accepting CDELTjs, jCDLns, and TCDLns as
plain synonyms for, respectively, CDj_js, jjCDns, and TCn_ns (rather
than deprecating some of them), just to have uniform rules for all of
them (I hope I'm not opening a can of worms here); with the
restriction that one cannot mix increments with a matrix: increments
are ignored when any CD matrix element is present.

I was trying not to get confused by the indices in Tables 1 and 7; but
shouldn't, in the latter, TCRPns be TCRPks?  It took me a while, but I
can see the rationale for the trio PVj_ms, jPm_ns, and TPm_ns.  It is
unfortunate that, in an effort to keep the column number at the end,
this clashes internally.  Maybe one should consider jPn_ms and TPn_ms;
I have my doubts whether these will ever become popular.

  - Arnold

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Arnold H. Rots                                         AXAF Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 81                              fax:  +1 617 495 7356
Cambridge, MA 02138                             arots at head-cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
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