AIPS HELP file for GUARD in 31DEC18
As of Tue Sep 25 13:36:38 2018
Type: Adverb (Real array, 2 elements)
Use: Specifies the width of the outer portion of the UV plane
which is to receive no data during the gridding process.
Subscript 1 refers to the U axis and 2 to the V axis and
the units are in fractions of the maximum U and V on the
plane being gridded.
Null Value: -1 => use only a few cells to avoid mathematical
0 => use 0.3 * sqrt(taper weight 0.3 from edge)
UVMAP....Make images and beam from calibrated single-source
UV data files.
HORUS....Make images and beam from multi-source UV data
files, applying calibration.
MX.......Make and deconvolve images from calibrated single-
source UV data files.
AIPS imaging allows the user to make a UV-plane grid with
data samples up to and off the edge of the plane. This is a
dangerous thing to do, however, since it introduces high-
frequencies into the image plane that cannot be deconvolved
properly. In those cases in which the user cannot include
all the data in the gridded plane (because a larger CELLSIZE
or smaller IMSIZE is desired), the user may discard data
automatically simply by allowing it to fall off the uv plane.
The resulting images will not deconvolve well. The user may
limit the data more severely, using either a circular limit
from adverb UVRANGE or a rectangular limit from GUARD. The
default value for GUARD is NOT enough to prevent high-
frequency effects in the deconvolution. Values more like 0.4
are needed for that in many cases.