[daip] Re: CLCOR

[Leonia Kogan]

Chris,

I have checked the recalculation of the apparent to the epoch
coordinates in CLCOR many times including comparison with SCHED
calculation of the coordinates. I am very confident that CLCOR carries
out the right calculations.

You wrote:

>but more importantly I run a
>modified version of CLCOR and it is calling JPREC with an epoch of
>2451983.5000000 (this is in subroutine SOUMOD following the comment "Loop
>through SU rows modifying the selected source position".

>Surely this is wrong?

I do not understand what does "modified version of CLCOR" mean.
I guess you added the print of JD.

If it is right then you need to print 'OBSDAT' also and compare it with ...
OBSDAT is the only parameter which control calculation of JD

            CALL JULDAY(OBSDAT, JD)

Leonia


----- Begin Included Message -----

>From Chris.Phillips at csiro.au Wed Nov 27 15:49 MST 2002
X-Authentication-Warning: lupus.atnf.CSIRO.AU: cphillip owned process doing -bs
Date: Thu, 28 Nov 2002 09:49:18 +1100 (EST)
From: Chris Phillips <Chris.Phillips at csiro.au>
X-X-Sender:  <cphillip at lupus.atnf.CSIRO.AU>
To: Eric Greisen <egreisen at cv3.cv.nrao.edu>,
        Leonia Kogan <lkogan at zia.aoc.NRAO.EDU>
Subject: Re: CLCOR
In-Reply-To: <200211261518.IAA28386 at bonito.aoc.nrao.edu>
MIME-Version: 1.0
X-Lines: 30
Status: RO

Gentlemen,

I started sending you another email yesterday, but I believe I somehow
lost it (I was writing it in stages checking stuff as I wrote it).

Anyhow, after my confusion on the mean/apparent difference in the SU table
I still think there is a minor problem.

With the original data (pre CLCOR), if I compare the mean and apparent
positions in the SU table, the coordinates agree to better than a mas with
what the SLALIB coco program computes if I use the epoch when the
calibrator first was observed (16 March 2001 -2:26:56). This is on the
second day (day 1) in the aips time convention (ie 15 March is 0 days).

When I run CLCOR it correctly changes the apparent position in the SU
table. However, it seems to update the mean position based on the epoch of
aips time 0, ie 15 March 0 UT. Using this epoch with coco the mean and
apparent are relatively close (a few mas) but more importantly I run a
modified version of CLCOR and it is calling JPREC with an epoch of
2451983.5000000 (this is in subroutine SOUMOD following the comment "Loop
through SU rows modifying the selected source position".

Surely this is wrong? I would have though it should use the same epoch as
originally used (ie the time the source first appears in the data set).

I can send you numbers to back up this claim if you like.

Cheers
Chris



----- End Included Message -----