AIPS HELP file for REWEIGHT in 31DEC26

As of Mon Jun 8 20:58:47 2026

HELP SECTION

REWEIGHT
Type: Adverb (Real(2))

Use: All uv data have associated weights which express the
     relative value of the data.  Internally, these weights are
     treated as statistical weights (i.e. 1 / variance
     (amplitude)).  These weights are used in making images but
     are modified by uniform weighting and tapering.  In
     practice, the weights coming into AIPS from non-AIPS
     calibration systems are in arbitrary units so a
     renormalization of the weights may be necessary when data
     sets are combined.

     The adverb REWEIGHT can be used to modify the relative
     weights of the two input data sets.  The simplest way to
     determine the appropriate relative weighting is to image each
     set of data independently in the same fashion as the desired
     final image (i.e. using the same IMSIZE, CELLSIZE, UVWTFN,
     UVBOX, and UVTAPER but not necessarily doing a deconvolution).
     All AIPS imaging tasks report the "sum of the gridding weights"
     in the message file.  This is the sum of the weights after all
     corrections are applied (this value has been written into the
     history file since 15JUL89).  REWEIGHT is a pair of values to be
     multiplied by the input weights for the first (1) and second (2)
     input uv data file.  These values should be set such that the
     two data sets will have the desired relative sum of weights.

     For example, if the two data sets before DBCON give a sum
     of gridding weights of 1.0E5 and 2.0E2 when imaged by IMAGR AND
     you wish to make them contribute equally to the final image then
     use: REWEIGHT = 1.0,1.0e5/2.0e2 (or 1, 500).

     REWEIGHT is also used by a variety of tasks for various
     re-weighting purposes.

Null value: 0 will be interpreted as 1.0

Tasks:
   BSGEO.........Beam-switched Az-El image to RA-Dec image translation
                 REWEIGHT(2) minimum convolved weight.
   BSGRD.........Task to image beam-switched single-dish data
                 REWEIGHT type output, min convolved weight
   DBCON.........Used to concatenate 2 uv data sets.  REWEIGHT described
                 above in detail.
   DSKEW.........Geometric interpolation correction for skew. REWEIGHT
                 interpolation halfwidth, min fraction good pixels
   FLATN.........Re-grid multiple fields into one image incl sensitivity
                 REWEIGHT interpolation halfwidth, min fraction good
                 pixels
   OGEOM.........Simple image rotation, scaling, and translation
                 REWEIGHT interpolation halfwidth, min fraction good
                 pixels
   OHGEO.........Geometric interpolation with correction for 3-D effects
                 REWEIGHT interpolation halfwidth, min fraction good
                 pixels
   SDGRD.........Task to select and image random-position single-dish
                 data.  REWEIGHT type output, min convolved weight
   SDIMG.........Task to select and image random-position single-dish
                 data.  REWEIGHT type output, min convolved weight
   SYSOL.........Undoes and re-does nominal sensitivity application for
                 Solar data   REWEIGHT does additional scaling of
                 visibilities, weights.
   TVIEW.........Display image cube in all 3 transpositions with
                 rotation & reference.  REWEIGHT interpolation
                 halfwidth, min fraction good pixels
   TYAPL.........Undoes and re-does nominal sensitivity application
                 REWEIGHT does additional scaling of visibilities,
                 weights.

EXPLAIN SECTION