Date: Tue, 30 Nov 2004 21:58:03 -0400
From: Mikael Lerner 
To: astronomy, Arun Venkataraman, Phil Perillat
Cc: robert.minchin, Robbie Auld,
     Riccardo Giovanelli,
     Martha P. Haynes,
     Mary Putman
Subject: Correction of WAPP FITS-file software

Hej!

The software writing the WAPP FITS-files was changed on 30 November to correct 
a bug affecting the positional information (and all the keywords listed in 
earlier emails regarding problems with the interpolations of telescope 
positions).

Phil has discovered a bug consisting of an error in the sign of the tracking 
error offset used. The FITS-writer has up until now calculated the actual 
telescope position by taking the commanded position and adding the tracking 
error. Unfortunately, the tracking error is defined in the opposite sense - 
the correct way to get the actual position is thus to SUBTRACT the tracking 
error from the commanded position.

This problem has now been corrected.

All spectral-line FITS-files taken up until 30 November are affected by this 
bug. However, since tracking errors typically are <1-2", the effects are 
rather small.

The only time you will see large errors in the positional information is if 
you were taking data while the telescope still were slewing towards your 
source.

Regards,

Mikael