Keywords: imager

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### UV table data format

A uv table is a specific 2-D Gildas table, with a few additional informations in the header, and a special interpretation of the data organisation.

In a standard uv table, each line describes a visibility. Here a line designate either the first or second axis of the table, and a column the other one. uv tables may appear in both orders. The default one is line on 1st axis (`.uvt` ordering, used by most application). The `.tuv` ordering obtained by a 21 transposition is used essentially for display, as in this case the column has the same meaning as for the magenta`COLUMN` of red GREG.

The number of lines of a uv table is thus the number of visibilities described in the table. Each column of the table stores a particular property of the visibilities, namely:

Column 1
  U in meters;
Column 2
  V in meters;
Column 3
  W in meters or Scan number;
Column 4
  Observation date (integer red CLASS/red CLIC Day Number2);
Column 5
  Time in seconds since 0:00 UT of above date;
Column 6
  Number of the first antenna used to measure the visibility;
Column 7
  Number of the second antenna used to measure the visibility;
Column 8
  Real part for the first frequency channel;
Column 9
  Imaginary part for the first frequency channel;
Column 10
  Weight for the first frequency channel;
Columns 11-13
  Same as column 8-10 but for the second frequency channel, or for the second Stokes parameter of this channel.
...
  etc...for all channels
Columns N-ntrail+1 ... N
  Trailing columns after the channel visibilities.

If a uv table describes `nvis` visibility spectra composed of `nchan` frequency channels, each with `nstokes` Stokes parameters, the size of the table will thus be: `nvis` lines of `7+3*nchan*nstokes+ntrail` columns, where `ntrail` is the number of trailing columns.

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