Basic Information on wsrtfits

Task: wsrtfits
Purpose: Conversion between MIRIAD and UVFITS format from WSRT
Categories: data transfer

WSRTFITS is a task for reading in WSRT UVFITS files into Miriad.
It is a modified version of the task FITS. Earlier versions
were also known as IVCFITS.

FITS is a MIRIAD task, which converts image and uv files both from
FITS to Miriad format, and from Miriad to FITS format. Note that
because there is not a perfect correspondence between all information
in a FITS and Miriad file, some information may be lost in the
conversion step. This is particularly true for uv files.

WARNING: When writing uv FITS files, fits can only handle single
source, single frequency band, single array configuration. Minimal
checks are made to see that these restrictions are observed!

Key: in
Name of the input file (either a FITS or MIRIAD file name, depending
on OP). No default.

Key: op
This determines the operation to perform. Possible values are:
  "uvin"    Convert FITS uv file to Miriad uv file.
  "uvout"   Convert Miriad uv file to FITS uv file.
  "xyin"    Convert FITS image file to Miriad image file.
  "xyout"   Convert Miriad image file to FITS image file.
  "print"   Print out a FITS header.
There is no default.

Key: out
Name of the output file (either a MIRIAD or FITS file name, depending
on OP). If op=print, then this parameter is not required. Otherwise
there is no default.

Key: line
Line type of the output, when op=uvout. This is of the form:

  linetype,nchan,start,width,step

"Linetype" is either "channel", "wide" or "velocity". "Nchan" is
the number of channels in the output.

Key: select
Normal uv selection, used when op=uvout.

Key: stokes
Normal Stokes selection, used when op=uvout

Key: options
These options applies for op=uvin only.
  compress Store the data in compressed uv format.
  nochi    Assume that the parallactic angle of the telescope is
           a constant 0 (or that the data are from circularly polarised
           feeds and have already been corrected for parallactic angle).
  nolefty  Assume that the FITS antenna table uses a right-handed
           coordinate system (rather than the WSRT left-handed
           system). 

These options for op=uvout only.
  nocal    Do not apply the gains table to the data.
  nopol    Do not apply the polarization leakage table to the data.
  nopass   Do not apply the bandpass table correctsions to the data.

This option applies for op=xyin only.
  dss      Use the conventions of Digital Sky Survey FITS files,
           and convert (partially!) its header.
  nod2     Use the conventions of NOD2 FITS files.

Key: velocity
Velocity information. This is only used for op=uvin,
and is only relevant for line observations. The default is
to use the information present in the FITS header. The
"velocity" parameter allows this information to be overriden or
the velocity system to be changed.

Within each line visibility data-set, Miriad stores the velocity
of the observatory wrt a rest frame. This allows account to be taken
of this when determining channel velocities.

The fits task will determine the observatory velocity either by being
given a velocity at a given channel (wrt a rest frame) or by using
a model of Earth and solar system motion (accurate to 0.005km/s).

The "velocity" parameter can be used to specify the velocity of
a particular channel. The parameter consists of three values:
the velocity system of the reference value, the reference value
and the reference channel, viz:
   velocity=velsys,refval,refchan
Possible values for the velocity system are:
  lsr     Velocity is the radio definition wrt the LSR frame.
  bary    Velocity is the radio definition wrt the barycenter.
  optlsr  Velocity is the optical definition wrt the LSR frame.
  optbary Velocity is the optical definition wrt the barycenter.
  obs     Velocity wrt the observatory.
  
The reference value gives the velocity, at the reference channel,
in km/s. If the reference value and reference channel are
omitted, a model of Earth and solar system motion is used to
determine the appropriate information.

For example:
  velocity=lsr,30,1
indicates that the first channel has radio LSR velocity of 30 km/s.
The observatory velocity, relative to LSR, can then be computed.

Alternately:
  velocity=lsr
indicates that fits is to determine the observatory velocity
wrt the LSR frame using an appropriate model.

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