[daip] CVEL suggestion

[Lincoln Greenhill]

Dear Leonia,

I think that my attempt to suggest a half-measure has caused some
confusion and it is not worth straightening out. Instead, I'll restate my 
thoughts.  I note  that I agree with the jist of Ketan's recent email.

I recommend that CVEL use the observing frequency, the date
of observation, and the rest frequency (supplied by the user) to compute
the velocity that belongs in the reference pixel.  This velocity would be
the same one that the user specifies in SCHED.  Afterwards, CVEL
shifts the spectra to achieve this velocity in the appropriate pixel. 

In this way CVEL would give the aips user exactly what he/she requested in
planning observation with a minimum of effort on the part of the user.

Right now, the user must go through more steps than is necessary to
achieve the right velocity in the right pixel. I would not suggest this
improvement since I know NRAO is shorthanded BUT every aips
user/spectral-line observer with whom I have worked has at least a few
times botched the processing that is currently required by aips. 


Regards,

Lincoln

P.S.  I note that I suggest creation of a separate mode for CVEL so that
the user is still free to shift spectra arbitrarily.  As well, I have
deliberately ignored VELDEF and VELTYP in my text, though these must also
be specified in my suggested processing scheme.

  
Lincoln J. Greenhill      Harvard-Smithsonian Center for Astrophysics 
Radio & Geoastronomy Division, 60 Garden St, Cambridge, MA 02138, USA
Telephone:  1 617-495-7194             FAX:  1 617-495-7345
Internet:  greenhill at cfa.harvard.edu   http://cfa-www.harvard.edu/~lincoln