; SHIFT
;---------------------------------------------------------------
;! specifies a position shift
;# ADVERB IMAGING COORDINATES
;-----------------------------------------------------------------------
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;-----------------------------------------------------------------------
SHIFT     LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC
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SHIFT
Type:  Adverb (Real array, 2 elements)
Use:   Specifies a change or shift of an image location.  The first
       element specifies a shift Eastward (lower X-pixel value).  The
       second element specifies a shift Northward (larger Y-pixel
       value).  Thus if both are > 0, the resulting map center is to the
       Northeast of the input (or the source appears to move down and to
       the right).

       The shift is no longer in SIN projected coordinates, so the SHIFT
       distances measured from an image are NOT exaxctly the number of
       pixels of offset multiplied by the pixel scale.

Null Value:  NONE  ( 0 => no shift)

The shifts are now (15OCT99) simpler to specify since they are in arc
seconds at the reference point.  They are simply the apparent
difference in position on the image ( (Xpix - Xpix_0) * Cell_X,
(Ypix - Ypix_0) * Cell_Y ) at least for small differences.  For large
shifts, use IMXY to give you RA and Dec and then compute the shifts
as:
        SHIFT(1) = cos (Dec_0) * (RA - RA_0)
        SHIFT(2) = Dec - Dec_0
in arc seconds.  The _0 refers to the reference coordinate.

Tasks:
   BSGRD.........Task to image beam-switched single-dish data.
   DFTIM.........Makes image of DFT at arbitrary point showing time vs
                 frequency.  SHIFT sets the location to which the data
                 are shifted.
   DFTPL.........Plots DFT of a UV data set at arbitrary point versus
                 time.  SHIFT sets the arbitrary point.
   FACES.........Makes images of catalog sources for initial calibration.
   FRPLT.........Task to plot fringe rate spectra.
   GSCAT.........Reads Fits Guide star catalog file.  SHIFT gives the
                 RA and Dec of field.
   HAFIX.........Recomputes u,v,w when time is hour angle (UVdata is
                 output of TI2HA).
   IM2UV.........Converts an image to a visibility data set.
   POSSM.........Task to plot total and cross-power spectra.
   SCMAP.........Imaging plus self-calibration loop with editing.
   SDGRD.........Task to select and image random-position single-dish
                 data.
   SDIMG.........Task to select and image random-position single-dish
                 data.
   SETFC.........Makes a BOXFILE for input to IMAGR.
   TBAVG.........Time averages data combining all baselines.
   UVFIX.........Recomputes u,v,w for a uv database.
   UVLIN.........Fits and removes continuum visibility spectrum, also can
                 flag.  Data are SHIFTed before the fit, fitted, and
                 then shifted back.
   UVLSD.........Least squares fit to channels and divides the uv data.
                 Data are SHIFTed before the fit, fitted, and then
                 shifted back.
   UVLSF.........Least squares fit to channels and subtracts from uv data.
                 Data are SHIFTed before the fit, fitted, and then
                 shifted back.
   UVMAP.........Makes images from calibrated UV data.
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