[daip] convert ra-dec to az-el

[Eric Greisen]

Niruj Mohan Ramanujam wrote:
> Hello,
> 
> I was wondering if there is a task in AIPS or in some other public 
> software which can convert an (all sky) image in RA-Dec to an 
> azimuth-elevation image for a given place and time ?
> 

Actually there is not in AIPS.  It is not a useful coordinate for 
ordinary images for reasons given below.  I could see how it might be 
useful for very low frequency imaging but we do not have it.

For one - the image probably took some time to observe as so the azimuth 
and elevation change while observing.  This is quite amazing in 
single-dish observing where constant elevation tracks are done.  The 
resulting image in sky coordinates is distinctly non rectangular. 
Therefore we have not made a verb to mess with headers in that way.  It 
could be done I suppose but it would be a can of worms if users actually 
started believing it.

Eric Greisen