README.rst

uvplot

A simple package to make nice plots of deprojected interferometric visibilities, often called uvplots. It can be installed inside the NRAO CASA package (see instructions below) and has functionalities to export visibilities from the MS Table format to ASCII. Available on the Python Package Index.

The current version implements the basic plotting functionality.

Features on the road map:

• handle MS tables with spectral windows with different number of channels;
• choose specific channels to export;
• import visibilities from ASCII to MS Table.

If you are interested, have feature requests, or encounter issues, consider creating an Issue or writing me an email. I am happy to have your feedback!

Installation

uvplot works on Python >=2.7 and >=3.6 and can be installed with:

pip install uvplot

To make uvplot available in CASA, run from the shell:

casa-pip install uvplot

where casa-pip is a tool that can be downloaded at https://github.com/radio-astro-tools/casa-python.

To upgrade uvplot to a newer version on your system, just run:

pip install --upgrade uvplot

To upgrade uvplot inside CASA use the --no-deps option to prevent casa-pip from automatically upgrading numpy and matplotlib (which is not allowed inside CASA and will lead to errors):

casa-pip install --upgrade --no-deps uvplot

uvplot has been tested on CASA versions >= 4.7.0.

Features

1) Plotting visibilities

This is an example plot:

created with uvplot:

import numpy as np
from uvplot import UVTable, arcsec
from uvplot import COLUMNS_V0       # use uvplot >= 0.2.6

wle = 0.88e-3         # Observing wavelength         [m]

dRA = 0.3 * arcsec    # Delta Right Ascension offset [rad]
dDec = 0.07 * arcsec  # Delta Declination     offset [rad]
inc = np.radians(73.) # Inclination    [rad]
PA = np.radians(59)   # Position Angle [rad]

uvbin_size = 30e3     # uv-distance bin [wle]

uv = UVTable(filename='uvtable.txt', wle=wle, columns=COLUMNS_V0)
uv.apply_phase(dRA, dDec)
uv.deproject(inc, PA)

uv_mod = UVTable(filename='uvtable_mod.txt', wle=wle, COLUMNS_V0)
uv_mod.apply_phase(dRA=dRA, dDec=dDec)
uv_mod.deproject(inc=inc, PA=PA)

axes = uv.plot(label='Data', uvbin_size=uvbin_size)
uv_mod.plot(label='Model', uvbin_size=uvbin_size, axes=axes, yerr=False, linestyle='-', color='r')

axes[0].figure.savefig("uvplot.png")

From version v0.2.6 it is necessary to provide the columns parameter when reading an ASCII uvtable. The columns parameter can be specified either as a parameter to the UVTable() command, or as the 2nd line in the ASCII file. The available columns formats are:

FORMAT          COLUMNS                                                 COLUMNS_LINE (copy-paste as 2nd line in the ASCII file)
COLUMNS_V0      ['u', 'v', 'Re', 'Im', 'weights']                       '# Columns      u v Re Im weights'
COLUMNS_V1      ['u', 'v', 'Re', 'Im', 'weights', 'freqs', 'spws']      '# Columns      u v Re Im weights freqs spws'
COLUMNS_V2      ['u', 'v', 'V', 'weights', 'freqs', 'spws']             '# Columns      u v V weights freqs spws'

To import an ASCII uvtable with 5 columns with uvplot < 0.2.6:

from uvplot import UVTable
uvt = UVTable(filename='uvtable.txt', format='ascii', columns=COLUMNS_V0)

and with uvplot >= 0.2.6:

from uvplot import UVTable
from uvplot import COLUMNS_V0  # ['u', 'v', 'Re', 'Im', 'weights']
uvt = UVTable(filename='uvtable.txt', format='ascii', columns=COLUMNS_V0)

2) Exporting visibilities from MS table to uvtable (ASCII)

Once installed uvplot inside CASA (see instructions above), it is possible to export the visibilities in mstable.ms to an ASCII table by executing these lines from a CASA shell:

CASA <1>: from uvplot import export_uvtable
CASA <2>: export_uvtable("uvtable.txt", tb, vis='mstable.ms')

Note: it is strongly recommended to perform a CASA split command with keepflags=False before exporting the uvtable. This ensures that only valid visibilities are exported.

The resulting uvtable.txt will contain u, v coordinates (in meters), Re(V), Im(V) visibility measurements (in Jansky), and weights. The table will also report the average wavelength (averaged among all selected spectral windows):

# Extracted from mstable.ms.
# wavelength[m] = 0.00132940778422
# Columns:  u[m]    v[m]    Re(V)[Jy]       Im(V)[Jy]       weight
-2.063619e+02       2.927104e+02    -1.453431e-02   -1.590934e-02   2.326950e+04
3.607948e+02        6.620900e+01    -1.680727e-02   1.124862e-02    3.624442e+04
5.752178e+02        -6.299933e+02   5.710317e-03    6.592049e-03    4.719500e+04
-9.198434e+02       -1.374651e+03   1.313417e-03    4.299262e-03    4.259890e+04
9.623210e+01        -4.631573e+02   7.731462e-03    -8.803369e-03   4.801395e+04
9.348914e+01        -5.191096e+02   3.759772e-03    4.754967e-04    4.748304e+04
1.108410e+03        -1.396906e+03   3.222965e-03    -5.164917e-03   4.690977e+04
[...]

By default export_uvtable exports all channels in all spectral windows. However, it is also possible to specify which spectral windows and channels to export. More details are given in the documentation of the export_uvtable() function.

Note: currently, export_uvtable only works for MS tables where all the spectral windows have the same number of channels (which, individually, can be larger than 1).

License and Attribution

If you use uvplot for your publication, please cite the Zenodo reference

@misc{uvplot_mtazzari,
  author       = {Marco Tazzari},
  title        = {mtazzari/uvplot: v0.1.1},
  month        = oct,
  year         = 2017,
  doi          = {10.5281/zenodo.1003113},
  url          = {https://doi.org/10.5281/zenodo.1003113}
}

uvplot is free software licensed under the LGPLv3 License. For more details see the LICENSE.

© Copyright 2018-2019 Marco Tazzari and contributors.

Contributors

Author:

• Marco Tazzari (University of Cambridge)

Contributions to the code base:

• Patrick Cronin-Coltsmann
• Grant Kennedy

Documentation

Check out the documentation.

Changelog

See the list of changes in all releases here.