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Index table         NXdssvv
 
 
 
A. Overview
 
   This extension table for a uv data set contains an index of the data
file.  There is an entry for each scan which gives the source, time
range, range of visibility numbers and other necessary information.
A scan is defined here to consist of a sequence of data from a given
subarray which terminates when the source, observing band or observing
mode changes or there is a gap in the data much longer than the
integration time of the data.
 
Names: The file name is NXdsssvv where d is disk number, sss=catalog
number and vv = version number.
 
B.  File structure.

     Logical records consist of the information for a single scan on a
single subarray.
 
    The file header record contains no KEYWORDs.
 
   Table entries:

       Title          Units   code      Description
  ----------------- --------- ---- -------------------------------------------
    TIME              Days    1E   Time of center of interval since 0h on
                                   reference day.
    TIME INTERVAL     Days    1E   Interval over which solution was obtained.
    SOURCE ID                 1I   Identification number of the source used.
    SUBARRAY                  1I   Subarray number
    START VIS                 1J   First visibility number (0 relative) of
                                   data in this scan.
    END VIS                   1J   Last visibility number (0 relative) of
                                   data in this scan.
    FREQ ID                   1I   Freq id number of the scan, only one
                                   number per scan at the moment.

C. User notes.

  The "code" column is element_count + basic type code.
basic type codes: D=Double precision, E=single precision,
   A=character, J=long integer, L=logical, I=short integer, X=bit.



     This table will in practice be used only by standard interface
routines.
 
D.  Routines to write NX files:
     The AIPS routines NDXINI and TABNDX will create/read/write NX tables.
Chapter 14 of "Going AIPS" given a detailed description of routines to
access tables files.
 
E.  Routines to access NX files:
     Chapter 14 of "Going AIPS" given a detailed description of routines to
access tables files.
