AIPS HELP file for OVRSWTCH in 31DEC18
As of Tue Oct 23 11:00:06 2018
Type: Adverb (scalar)
Use: To specify when OVERLAP >= 2 mode is changed to OVERLAP = 1 mode
while Cleaning single-Gaussian, multi-facet images in IMAGR.
The mode is switched when the peak residual reaches
abs(OVRSWTCH) Jy/beam. If OVRSWTCH < 0, ONEBEAM is changed to
TRUE for the OVERLAP = 1 portion of the Clean.
Null value: 0.0
Do not switch modes
IMAGR......Fourier transforms and Cleans uv data with wide-field,
interactive TV, and data weighting options.
In OVERLAP=2 mode, AIPS images all facets to begin with
and then Cleans only one. It subtracts the components
from the residual uv data, chooses another facet,
images it with the new residual data, Cleans it, and so
forth. This has the desirable attribute of avoiding
the sidelobes of the strong sources as they might
appear in other facets because they are subtracted
before those facets are imaged and Cleaned. OVERLAP=1
mode images all facets at once, Cleans them all, then
subtracts any components found in all factes from the
residual uv data, and then re-images and Cleans all
facets again. It may be appropriate to start in
OVERLAP=2 mode until the highest dynamic range
structures are removed and then, when the Cleaning gets
down near the noise levels, switch to OVERLAP=1 mode
for the last portion of the Clean. OVRSWTCH is used to
define the residual brightness level at which this
switch will occur.