Visibility

class Visibility(data=None, frequency=None, channel_bandwidth=None, phasecentre=None, configuration=None, uvw=None, time=None, antenna1=None, antenna2=None, vis=None, weight=None, imaging_weight=None, integration_time=None, polarisation_frame=<data_models.polarisation.PolarisationFrame object>, cindex=None, blockvis=None, source='anonymous', meta=None)

Bases: object

Visibility table class

Visibility with uvw, time, integration_time, frequency, channel_bandwidth, a1, a2, vis, weight as separate columns in a numpy structured array, The fundemental unit is a complex vector of polarisation.

Visibility is defined to hold an observation with one direction. Polarisation frame is the same for the entire data set and can be stokes, circular, linear The configuration is also an attribute

The phasecentre is the direct of delay tracking i.e. n=0. If uvw are rotated then this should be updated with the new delay tracking centre. This is important for wstack and wproject algorithms.

If a visibility is created by coalescence then the cindex column is filled with a pointer to the row in the original block visibility that this row has a value for. The original blockvisibility is also preserves as n attribute so that decoalescence is expedited. If you don’t need that then the storage can be released by setting self.blockvis to None

There are two visibility formats:

BlockVisibility is conceived as an ingest and calibration format. The visibility data are kept in a block of shape (number antennas, number antennas, number channels, number polarisation). One block is kept per integration. The other columns are time and uvw. The sampling in time is therefore the same for all baselines.

Visibility is designed to hold coalesced data where the integration time and channel width can vary with baseline length. The visibility data are kept in a visibility vector of length equal to the number of polarisations. Everything else is a separate column: time, frequency, uvw, channel_bandwidth, integration time.

Attributes Summary

antenna1
antenna2
channel_bandwidth
frequency
imaging_weight
index
integration_time
npol
nvis
time
u
uvdist
uvw
uvwdist
v
vis
w
weight

Methods Summary

size()

Return size in GB

Attributes Documentation

antenna1

antenna2

channel_bandwidth

frequency

imaging_weight

index

integration_time

npol

nvis

time

u

uvdist

uvw

uvwdist

v

vis

w

weight

Methods Documentation

size()

Return size in GB