[daip] Re: aips question

[Eric Greisen]

T. Nordgren writes:

 > 	Leonia Kogan suggested I contact you regarding
 > an aips problem I have been having. First, I should
 > say that I am running the 15APR97 aips distribution.

      That is so old that no one can say what it does.

 > 
 > My problem is that I am trying to combine uv-data sets
 > from two separate observing runs (using two different
 > arrays) where one run was done using epoch B1950
 > while the other was made using. Everything
 > else is the same.
 > 
 > DBCON rightly dies claiming the two sets are of different
 > epochs. When I use EPOSW to change the epoch
 > B1950 file to J2000, the header shows a rotation in the
 > declination axis. If I try to use DBCON to combine this 
 > new file with the original J2000 file, it dies claiming
 > the dec axis has unequal attributes.

     Try:
     KEYWORD='CROTAn'; GETHEAD      where n is axis of DEC with
                                    rotation
     ROTATE = - KEYVAL(1)
     GO UVSRT                       make sure SORT= whatever you want
     This should undo the rotation and correct the u,v to J2000.

 > 
 > Leonia suggested using UVFIX on the EPOSW'd B1950
 > file. This has the effect of removing the rotation from
 > the dec axis but DBCON still dies claiming unequal dec
 > axis attributes. Unfortunately now, I can't see that there
 > is any difference in the headers of the two files. The
 > dec axes look identical (as far as the header will allow
 > be to tell).

     The rotation may not be pure 0 and that old version cared way too
much about accuracy.

 > 
 > Do you have any suggestions? Leonia seemed to indicate
 > that you might know of some other series of tasks that
 > would transform the B1950 data into J2000 that
 > would allow me to combine it with the original J2000 file.
 > 
 > Simply put: how do I combine u-v spectral line data
 > files observed using different epochs?

Run a modern aips - what you have is not supported and full of
problems that have been fixed.  Modern versions offer so much more as
well.

ERic Greisen