From jhibbard@nrao.edu Fri Apr  2 16:08:36 2004
Date: Fri, 02 Apr 2004 17:43:00 -0500
From: John Hibbard <jhibbard@nrao.edu>
To: aips2-naug@zia.aoc.nrao.edu
Subject: Re: [Aips2-naug] Comments on Data Selection

I'll add my $0.02 to the GM data selection document.

I'd advise getting input from people who are used to
different reduction packages, esp. myriad & gipsy;
probably single dish stuff too.

Principal:
==========
The pricipal is your pal.

time:
=====
Should scan be a separate param? I agree with
Steve that yes it should be. If not, then perhaps
instead of "time", make it "timeslot" so "timeslot=1-3"
makes more sense.

field:
======
In GM's example, field=0-3 gives the first four fields.
But if you do a ms.summary(), the first field is labelled
as 1, not 0.

antenna:
========
I seems more natural to me that antenna='5' means '5 & *'
and "antenna='5,6,7'" means '(5,6,7) & *' rather than
'5 & 5' and '(5,6,7) & (5,6,7)'. But I could learn otherwise.

spw:
====
You can stride many things (e.g. uvrange for diff. fields or
sources), so I think channel averaging would make more sense
as a separate parameter. But I always process files with
multiple IF setups separately. Perhaps its best that
people who are used to processing multiple spw give their
opinions.

I am not thrilled about Steve's proposed unique striding
notation, but I'm sure its one of those things I'd get used
to. While I prefer 2:16/5/2/2 to 2:16_5+2^2, I do see
that it would be easier to recognize errors with a unique
syntax than a sequential one.

As for negative velocities, using () makes the most sense to
me, e.g. (-50)-(-76) km/s

literal strings:
================
I agree with Steve that these are probably needed. field="1-2"
makes the most sense to me.

uvdist:
=======
Yes, should be able to separately specify u,v,w


Overall, very good and a very worthwhile effort.

-john

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