Visibility Statistics
MS statistics (visstat)
The visstat task is provided to obtain simple statistics for a MeasurementSet, useful in regression tests.
The inputs are:
vis = '' # Name of Measurement Set or Multi-MS
axis = 'real' # Which values to use
datacolumn = 'data' # Which data column to use (data, corrected, model, float_data)
useflags = False # Take flagging into account?
spw = '' # spectral-window/frequency/channel
field = '1' # 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 = 'RR' # Select data based on correlation
scan = '' # scan numbers: ''==>all
array = '' # (sub)array numbers: ''==>all
observation = '' # observation ID number(s): '' = all
uvrange = '' # uv range: ''==>all; uvrange = '0~100klambda', default units=meters
timeaverage = False # Average data in time.
intent = '' # Select data by scan intent.
reportingaxes = 'ddid' # Which reporting axis to use (ddid, field, integration)
Running this task returns a record (Python dictionary) with the statistics, which can be captured in a Python variable. For example,
CASA <54>: mystat=visstat(vis='data/regression/unittest/setjy/ngc5921.ms', axis='amp', datacolumn='data', useflags=False, spw='', field='', selectdata=True, correlation='RR', timeaverage=False, intent='', reportingaxes='ddid')
CASA <55>: mystat
Out[55]:
{'DATA_DESC_ID=0': {'firstquartile': 0.023732144385576248,
'isMasked': False,
'isWeighted': False,
'max': 73.75,
'maxDatasetIndex': 12,
'maxIndex': 1204,
'mean': 4.511831488357214,
'medabsdevmed': 0.0432449858635664,
'median': 0.051963627338409424,
'min': 2.2130521756480448e-05,
'minDatasetIndex': 54,
'minIndex': 4346,
'npts': 1427139.0,
'rms': 16.42971891790897,
'stddev': 15.798076313999745,
'sum': 6439010.678462409,
'sumOfWeights': 1427139.0,
'sumsq': 385235713.187832,
'thirdquartile': 0.3004012107849121,
'variance': 249.57921522295976}}
CASA <56>: mystat['DATA_DESC_ID=0']['stddev']
Out[56]: 15.798076313999745
The options for axis are:
axis='amplitude' # or ('amp') axis='phase' axis='imag' (or 'imaginary') axis='real'
The phase of a complex number is in radians with range (−π, π).