Documentation on fits

Task: fits
Purpose: Conversion between MIRIAD and FITS image and uv formats
Categories: data transfer

        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.

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 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     Expect an image produced by the Digital Sky Survey,
                  and convert (partially!) its header.

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.