Visibility Header¶

class oskar.VisHeader¶

This class provides a Python interface to an OSKAR visibility header.

The oskar.VisHeader class encapsulates the small amount of metadata used to describe a visibility data set generated by OSKAR, and it will be saved as part of any visibility data files written by the oskar.Interferometer class.

To load the header data from an OSKAR visibility binary file (note this is not a CASA Measurement Set, although it can be converted into one), use the read() class method. This will return a tuple containing both the header data and also a handle to the binary file, which can be used to read subsequent oskar.VisBlock data structures from the same file.

The visibility data header for the current simulation can be returned using the method oskar.Interferometer.vis_header() if required.

Examples

To load the header from a file example.vis and print some values from it:

>>> (header, handle) = oskar.VisHeader.read('example.vis')
>>> print(header.num_blocks)
3
>>> print(header.num_times_total)
24
>>> print(header.num_channels_total)
3
>>> print(header.freq_start_hz)
100000000.0
>>> print(header.freq_inc_hz)
20000000.0
>>> print(header.phase_centre_ra_deg)
20.0
>>> print(header.phase_centre_dec_deg)
-29.999999999999996

amp_type¶: Returns the OSKAR data type of the visibility amplitude array.

channel_bandwidth_hz¶: Returns the width of each frequency channel, in Hz.

coord_precision¶: Returns the OSKAR data type of the baseline coordinate arrays.

freq_inc_hz¶: Returns the frequency channel increment, in Hz.

freq_start_hz¶: Returns the frequency of the first channel, in Hz.

max_channels_per_block¶: Returns the maximum number of channels per visibility block.

max_times_per_block¶: Returns the maximum number of time samples per visibility block.

num_blocks¶: Returns the expected number of visibility blocks for a run.

num_channels_total¶: Returns the total number of frequency channels.

num_stations¶: Returns the number of stations.

num_tags_per_block¶: Returns the number of binary data tags per visibility block.

num_times_total¶: Returns the total number of time samples.

phase_centre_ra_deg¶: Returns the phase centre Right Ascension, in degrees.

phase_centre_dec_deg¶: Returns the phase centre Declination, in degrees.

time_start_mjd_utc¶: Returns the start time, as MJD(UTC).

time_inc_sec¶: Returns the time increment, in seconds.

time_average_sec¶: Returns the time averaging period, in seconds.

classmethod read(binary_file)¶

Reads a visibility header from an OSKAR binary file and returns it.

Parameters:	binary_file (str or oskar.Binary) – Path or handle to an OSKAR binary file.
Returns:	A two-element tuple containing the visibility header and a handle to the OSKAR binary file, opened for reading.
Return type:	tuple