18.31 UV_FIELDS

[CLEAN\]UV_FIELDS RaVar DecVar [Unit] [/CENTER Ra Dec] /FILE File

***** Experts Only **** Not intended for general use ******

Replace fields ID by Fields offsets in a Mosaic UV Table. This can only work for a Mosaic UV table with Fields offsets, or Phase center offsets. It cannot operate on a UV table with Pointing center offsets.

For files imported from UVFITS, the Fields offsets are found in the AIPS SU Table which is not decoded by the FITS command, but only through the DEFINE FITS command.

The UV_FIELDS command allows to convert the Field IDs column of the UV table into Phase Offsets columns, and insert the proper coordinates. Unit specifies the unit of the RaVar and DecVar variables. It can be DEGREE, MINUTE, SECONDS, RADIAN or ABSOLUTE.

If ABSOLUTE, RaVar and DecVar are assumed to character variable arrays handling the Right Ascension and Declinations of the fields expressed in sexagesimal format.

The typical use is after a DEFINE FITS A File.uvfits command, which gives the (Ra,Dec) positions of the field centers in Degrees in A%aips_su%col%raepo and A%aips_su%col%decepo variables:

     fits File.uvfits to File.uvt
     define fits A File.uvfits HEADER
     compute ra mean a%aips_su%col%raepo
     compute dec mean a%aips_su%col%decepo
     define double ra dec
     define char*16 cra cdec
     let cra ra /sexag d H
     let cdec dec /sexag d d
     !
     uv_fields a%aips_su%col%raepo a%aips_su%col%decepo DEGREE -
       /FILE File.uvt /CENTER 'CRa' 'CDec'
     !

This command is used in the fits_to_uvt.ima script. Note that a proper use also requires to set the reference coordinate to Ra and Dec consistently in the UV Table.