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#                                                                             #
# The Friendly Virtual Radio Interferometer                                   #
# by Cormac Purcell and Roy Truelove, Macquarie University, Sydney.           #
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INTRODUCTION:

The Friendly Virtual Radio Interferometer (VRI) is designed to simulate
astronomical observations using linked arrays of radio antennas in a technique
called earth rotation aperture synthesis. As the successor to the original
VRI by Nuria McKay, Derek McKay and Mark Wieringa, it focuses on simulating
the effect of combining different antenna layouts. This is necessary to achieve
good uv-coverage using radio interferometers with only a few antennas like the
Australia Telescope Compact Array.


INTERFACE:

The interface is (hopefully) very intuitive and is split into a control window
and a plotting window. The plotting window can be maximised and buttons at the
lower-right enable jumping quickly between the two windows. The control window
allows you to:

* Plot the layout of the antennas in an array configuration for a particular
  telescope.
* Create a list of observations to be simulated using different array
  configurations, over different time ranges (hour angles) and with different
  sampling cadence.
* Load in a model image and set its angular scale on the sky.
* Apply the uv-coverage of the observations to the model to simulate an
  observation. 

The plotting window shows inputs, outputs and intermediate steps in the
process: model image, fast Fourier transform (FFT) of the model, plot
of uv-coverage, filtered model FFT, synthesised beam and final
observed image.

See the help menu in the for a list of step-by-step instructions.


DEFINING CUSTOM ARRAYS:

The location and layout of antennas in each array configuration is defined in
ASCII files under the 'arrays/' directory. You can define your own arrays by
copying the existing templates and supplying a list of coordinate offset
in the East and North directions, in units of meters. The software will read
these on start-up and they will appear in the list of available arrays. Note
that the combination of 'telescope' + 'array' name must be unique.


CAVEATS:

This software is designed to be a simple 'quick-look' tool and ignores lots of
effects such as non-co-planar arrays, time averaging, multi-frequency synthesis
etc. It also sets the sampling grid in the Fourier domain from the extent and
pixel spacing of the input image, which can result in under-sampled synthesised
beams and artefacts. At the moment, the observing simulations are assumed to be
noise-free and no attempt is made at calculating sensitivities. Tasks to
perform robust simulations of an interfometric observation exist in CASA,
MIRIAD and AIPS, but are more difficult to use.


CREDITS:

The Friendly Virtual Radio Interferometer tool was written by Cormac Purcell
and Roy Truelove at Macquarie University, Sydney. Questions, comments, feature
requests and bug reports should be directed to 'cormac.purcell (at) mq.edu.au'.


LICENCE:

Copyright (c) 2017 Cormac R. Purcell and Roy Truelove.
Released under the MIT licence.