MS statistics (visstat)

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2.2.9 MS statistics (visstat)

ALERT: This is still a prototype task.

The visstat task is provided to obtain simple statistics for a Measurement Set, useful in regression tests.

The inputs are:

#  visstat :: Displays statistical information from a measurement set
vis              =      ’’   #  Name of input visibility file
axis             =   ’amp’   #  Which values to use
   datacolumn    =  ’data’   #  Which data column to use (data, corrected, model)

useflags         =    True   #  Take flagging into account?
spw              =      ’’   #  spectral-window/frequency/channel
field            =      ’’   #  Field names or field index numbers: ’’==>all, field=’0~2,3C286’
selectdata       =    True   #  More data selection parameters (antenna, timerange etc)
   antenna       =      ’’   #  antenna/baselines: ’’==>all, antenna = ’3,VA04’
   timerange     =      ’’   #  time range: ’’==>all, timerange=’09:14:0~09:54:0’
   correlation   =      ’’   #  Select data based on correlation
   scan          =      ’’   #  scan numbers: ’’==>all
   array         =      ’’   #  (sub)array numbers: ’’==>all
   uvrange       =      ’’   #  uv range: ’’==>all; uvrange = ’0~100klambda’, default units=meters

async            =   False   #  If true the taskname must be started using visstat(...)

Running this task returns a record (Python dictionary) with the statistics, which can be captured in a Python variable. For example,

CASA <42>: mystat = visstat(’ngc5921.demo.ms’,axis=’amp’,datacolumn=’corrected’,field=’0’)

CASA <43>: mystat
  Out[43]:
{’CORRECTED’: {’max’: 51.938671112060547,
               ’mean’: 14.796444141750133,
               ’medabsdevmed’: 0.28020858764648438,
               ’median’: 14.764373779296875,
               ’min’: 0.81362706422805786,
               ’npts’: 514916.0,
               ’quartile’: 0.56053066253662109,
               ’rms’: 14.829294204711914,
               ’stddev’: 0.98650836609147285,
               ’sum’: 7618925.8316934109,
               ’sumsq’: 113234125.12642419,
               ’var’: 0.97319875636846753}}

CASA <44>: print mystat[’CORRECTED’][’stddev’]
0.986508366091

The options for axis are:

    axis=’amplitude’      #    or (’amp’)
    axis=’phase’
    axis=’imag’
    axis=’scan_number’
    axis=’flag’

The phase of a complex number is in radians with range (-π,π).

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