Heuristic editing

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Heuristic editing

Several simple heuristic editing methods are available in the flagger tool. These methods act on the data selected as described above, but add an additional heuristic constraint.

For example, it is usually desirable to flag the auto-correlation data from the VLA (otherwise, the imager tool may attempt to use it in image formation as if it were single dish data). To do this:

fg.reset();                   # Reset the data selection
fg.flagac();                  # Flag the auto-correlations

It is often the case that the VLA data near the beginning of scans (e.g. after field or frequency band changes is bad. To flag such data, use the flagger.quack function. For example, to remove 20 seconds of data at the beginning of scans (defined by gaps larger than 30 seconds) on field 3:

fg.reset();                   # Reset the data selection
fg.setids(fieldid=3);         # Limit quack to fieldid=3 only

fg.quack(scaninterval='30s',  # Trial run of quack
         delta='20s',
         trial=T);

fg.quack(scaninterval='30s',  # Quack it
         delta='20s');

Automated editing methods are available in the flagger and autoflag tools. These include clipping, median flagging and related methods.

For example, to clip data outside of a specified amplitude range with the flagger tool:

fg.setids(fieldid=2, spwid=[1,2]);    # Select field, spw
fg.setpol(pol=[1,4]);                 # Select polarizations 1,4
                                      #  (e.g., RR and LL)
fg.filter(column='DATA',              # Flag data if, DATA column
          operation='range',          #   Amplitudes are outside
          comparison='Amplitude',     #   1.12-1.34
          range=['1.12Jy','1.34Jy'],
          fullpol=T,                  # Extend flags to pols and
          fullchan=T);                #  and chans that weren't 
                                      #  tested

The autoflag tool has more sophisticated algorithms. Examples of its use will be included here in the near future.

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