Processing Pointing Data using POINT_PROCESS

Summary

To process pointing data, one has to:

• Load the data for an antenna into the program,
• Assess which are the main components of the pointing error, and 'set' those to calculate the size of the pointing error,
• Calculate what this error is,
• Interate through steps 1-3 for each antenna,
• Write the errors to a file (done by quitting from the program) and
• Installing the calculated errors in the antennas.

Procedure

• Starting the program and Loading Data

  To run the program, you have to be on NOEL (where PNTCOM is installed), and you have to know the start record and end record.

  $ set def OBS$1:[CATAG.WORK]
  $ run point_process
      /xs                (PGplot device)
      8                  (example start record - use the CATAG value)
      23                 (ditto)
      16                 (put in the bad CATAG records - shadowing etc.)
                     (no more bad records)
  

  You should now have a "point>" prompt.
  Load the data for each antenna with the load command, e.g.

  point> load
           3            (select the antenna)
                    (select the IF's you want to use)
  

  Note if you have a bad scan, you have to make sure that it is skipped when you are loading the data in. We can now select which IF's get used - great for when some IF is dead e.g. 5C or similar. Note that because I use antenna gain solving in CATAG to determine the offsets, if you discard an IF on a single antenna, you should do it for them all.
  

• Assessing the main components of an Antenna Pointing Error

  There are 10 (semi) independent parameters which can be 'set' or 'unset' and the calculation is then done.
  In general:
  • EA (az encoder error)
  • FX (el encoder error)
  • AX (squint)
  • AY (the other squint)
  are will be all that is needed to calculate pointing errors. Set or Fix parameters, then caculate the pointing errors. After you calculate the pointing errors, the RMS error on this calculation should be less than 10 arc sec - in general it will be better than 5 arc sec.
  Be very careful about modifying the CA06 parameters - they have been constant for quite some time, and in general, we find that trying to 'fix' them actually puts you back.
  

• Writing PARAMS file

  Now for the trick... When you quit from POINT_PROCESS, a file is written (params.dat) which has the pointing parameters that should be applied, derived from the last calculation that you did. Thus, if for some reason you don't do any calculations for one antenna (e.g. antenna 6, or if the program crashed part way through) you will have a file with NO pointing parameters for a given antenna - not a good thing. The way to handle this is to do it all again!!! (You get quicker) With an antenna that you are not changing, unset all the parameters, and calculate the errors - it will add 0 to the current pointing parameters.
  

• Installing the PARAMS into the ACCs

  (This is also described in the pointing documentation)

  $ copy params.dat at$acc:pparams.dat
  $ run ppload
      e             (make it a global solution)
      at$acc:pparams.dat   (again, this is the default)
  
  $ cain
      e         (expert mode)
      y         (confirm)
      p         (load pointing parameters)
      y         (default - use the new global values)
      *         (all antennas)
      y         (do the initialisation)
  

Now check how things have gone.

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Original: Robin Wark (16-Oct-1998)
Modified: Robin Wark (16-Oct-1998)