[daip] forwarded message from Eric Greisen

[Eric Greisen]

------- start of forwarded message (RFC 934 encapsulation) -------
Received: from primate.aoc.nrao.edu (primate [146.88.1.117])
	by zia.aoc.NRAO.EDU (8.9.3/8.9.3) with ESMTP id QAA02291;
	Tue, 9 Jul 2002 16:00:37 -0600 (MDT)
Received: (from egreisen at localhost)
	by primate.aoc.nrao.edu (8.11.6/8.11.6) id g69M0bl30209;
	Tue, 9 Jul 2002 16:00:37 -0600
Message-Id: <200207092200.g69M0bl30209 at primate.aoc.nrao.edu>
X-Authentication-Warning: primate.aoc.nrao.edu: egreisen set sender to egreisen at nrao.edu using -f
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
In-Reply-To: <Pine.GSO.4.05.10207091100090.26328-100000 at polaris.phys.yorku.ca>
References: <Pine.GSO.4.05.10207091100090.26328-100000 at polaris.phys.yorku.ca>
X-Mailer: VM 6.35 under Emacs 20.7.1
Content-Type: text/plain; charset=us-ascii
From: Eric Greisen <egreisen at cv3.cv.nrao.edu>
To: Michael Bietenholz <michael at polaris.phys.yorku.ca>
Subject: Re: [daip] FITS /astrometry question
Date: Tue, 9 Jul 2002 16:00:37 -0600

Michael Bietenholz writes:
 >   I have noticed that AIPS (at least TVLAB, CELGAL and EPOSW) seems to
 > ignore the rotation on the first axis, and rotate both axes according
 > to the listed rotation of the 2nd (decl) axis.  Am I correct in assuming
 > that AIPS (and FITS?) requires the axes to be perpendicular, so that
 > only 1 rotation angle is required, and that it uses the CROTA2 or
 > the AIPS-header rotation of the 2nd axis for this rotation?

     There can be only one rotation of celestial axes and by
convention we put it on the latitude axis.  Skew is not a rotation.
You should be aware of the WCS effort which you can find on my home
page:
             http://www.aoc.nrao.edu/~egreisen
The first two papers are about to be an IAU Standard.

Eric

 > 
 >               thanks,             michael
 > 
 > _______________________________________________
 > Daip mailing list
 > Daip at listmgr.cv.nrao.edu
 > http://listmgr.cv.nrao.edu/mailman/listinfo/daip
 > 

------- end -------