AIPS HELP file for APGS in 31DEC22
As of Tue Nov 28 23:23:37 2023
APGS: Task which deconvolves the Gerchberg-Saxton way.
INNAME Image name (name)
INCLASS Image name (class)
INSEQ 0.0 9999.0 Image name (seq. #)
INDISK 0.0 4.0 Image disk drive #
IN2NAME Image name (name)
IN2CLASS Image name (class)
IN2SEQ 0.0 9999.0 Image name (seq. #)
IN2DISK 0.0 4.0 Image disk drive #
OUTNAME Image name (name)
OUTCLASS Image name (class)
OUTSEQ -1.0 9999.0 Image name (seq. #)
OUTDISK 0.0 4.0 Image disk drive #
GAIN -1.0 1.0 GS loop gain
NITER 0.0 32767.0 Maximum # of GS components
DOTV -1.0 1.0 TV display of residuals?
NBOXES 0.0 10.0 Number of boxes for CLEAN
BOX 0.0 4096.0 Four coordinates for each box
BADDISK -1.0 1000.0 Disks to avoid for scratch.
OFFSET -1.0 1000.0 Beam offset for stabilisation
Use: APGS deconvolves the dirty beam from the dirty map thus
producing a map with the units of brightness (Jy/pixel).
Conversion to other units e.g. KELVIN can be done with AXDEFINE.
APGS may be restarted if further improvement is desired. This
program is slow but should be comparable to APCLN if the map
contains many picture elements. The task CONVL may be used to
convolve the map to the resolution produced by a CLEAN program.
The algorithm used in the program is due to Gerchberg and
Saxton. The GS map is constrained to be non-zero, and positive,
only in the regions defined by the BOXes. Data and image plane
constraints are imposed alternately while transforming to and
from the image plane. If the BOXes are chosen to surround the
source snugly then the algorithm will converge faster and will
have more chance of finding a unique image. To obtain smoother
images a non-zero value of OFFSET may be chosen. This adds a
delta function to the beam as is done in PHCLN. Try values of
0.01 - 0.2 for OFFSET.
This is an experimental program; please relay any
complaints etc. to Tim Cornwell at the VLA
INNAME......The dirty image name. Standard defaults.
INCLASS.....The dirty image class. Standard defaults.
INSEQ.......The dirty image seq. #. 0 => highest.
INDISK......The dirty image disk drive #. 0 => any
IN2NAME.....The beam image name. blank => actual
INNAME, otherwise standard defaults.
IN2CLASS....The beam image class. Standard defaults
except blank => 'RBEM' if INCLASS = 'RMAP'
'LBEM' if INCLASS = 'LMAP'
'IBEM' if INCLASS = anything else
Only positive images can be made so that Q,U,V
GS images are impossible. ( One day....)
IN2SEQ......The beam image seq . #. 0 => actual INSEQ
IN2DISK.....The beam image disk drive #. 0 => any
OUTNAME.....The GS image name. blank => Standard defaults
based on INNAME.
OUTCLASS....The GS image class. Standard behavior with
default = 'RGS ' if INCLASS = 'RMAP'
'LGS ' if INCLASS = 'LMAP'
'IGS ' if INCLASS = anything else
OUTSEQ......The GS image seq. #. 0 => highest unique
If >0; image will be created if new,
overwritten if image name exists.
OUTDISK.....The GS disk drive no. 0 => highest with space
GAIN........The GS loop gain. 0 => 0.01, for most cases
0.02 will work well. NOTE that this only
affects the route taken to the final GS
image NOT the image itself.
NITER.......GS iteration limit. 0 => 20
DOTV........Display GS map on TV channel 1. > 0 => yes.
If true, you may stop the GS ing with TV button
D after each GS map is displayed.
NBOXES......The number of rectangular boxes. The GS image is
non-zero only within these boxes. 0=>1
BOX.........A 4x10 array with the BLC and TRC of each box.
0 => use inner quarter of input map (first box)
0 => ignore box (boxes 2 - 10)
BADDISK.....This array contains the numbers of disks on which
it is desired that scratch files not be located.
BADDISK has no effect on input and output maps.
OFFSET......Add a blip of size offset to the beam before
deconvolving. If the blip is positive then a
smoother image will result at the cost of a
slightly poorer fit to the data. Try values in the
range 0.01 to 0.2.