AIPS HELP file for COMB in 31DEC24
As of Sat Apr 20 0:39:35 2024
COMB: Task to combine in many ways two overlapping images
INPUTS
INNAME First image name
INCLASS First image class
INSEQ 0.0 9999.0 First image seq. #
INDISK 0.0 9.0 First image disk drive #
IN2NAME Second image name
IN2CLASS Second image class
IN2SEQ 0.0 9999.0 Second image seq. #
IN2DISK 0.0 9.0 Second image disk drive #
IN3NAME First noise image name
IN3CLASS First noise image class
IN3SEQ 0.0 9999.0 First noise image seq. #
IN3DISK 0.0 9.0 First noise image disk #
IN4NAME Second noise image name
IN4CLASS Second noise image class
IN4SEQ 0.0 9999.0 Second noise image seq. #
IN4DISK 0.0 9.0 Second noiseimage disk #
DOALIGN -2.0 1.0 Should images be coincident?
(See HELP.)
OUTNAME Output image name
OUTCLASS Output image class
OUTSEQ -1.0 9999.0 Output image seq. #
OUTDISK 0.0 9.0 Output image disk drive #
BLC 0.0 4096.0 Bottom left corner
TRC 0.0 4096.0 Top right corner
OPCODE Algorithm type:
'SUM ','DIV ','SPIX','POLI',
'POLA','MULT','OPTD','CLIP'
'REAL','IMAG','MEAN','RM '
'POLC','SUMM'
APARM Parameters for algorithm:
(1) - (4) scale and offset
(8) > 0 => blank with 0.0
(9) Map1 clip level
(10) Map2 clip level
see HELP COMB
BPARM Noise/control parameters:
(1) Map1 noise level
-1 use 3rd image
0 ignore noise
(2) Map2 noise level
-1 use 4th image
0 ignore noise
(3) > 0 => output noise
in addition
(4) < 0.5 => clip w inputs
> 1.5 => clip w S/N
else => clip w noise
(5) minimum ok abs(S/N) or
maximum ok noise
(6) max output noise
0 -> any
see HELP COMB
DOHIST -3.0 1.0 -2 => copy 1st HI only
-3 => copy no HI files
HELP SECTION
COMB
Type: Task
COMB is a generalized task which combines two input images and,
optionally two input noise images, pixel by pixel to produce a new
cataloged image and, optionally, an image of the uncertainty in
the main output image. Numerous mathematical methods for
combining the images are provided. COMB has the ability to blank
the output values of the derived map on the basis of either its
error, its signal/noise ratio, or various cutoff levels.
The two input maps should be coincident. One may combine only
subimages if desired. COMB will combine two fully overlapping
n-dimensional images and it can combine each n-m dimension "plane"
of the first n-dimensional image with the single n-m dimension
"plane" of an n-m dimensional second image.
If the images are in JY/BEAM, COMB will scale images 2, 3, and 4
to be in the same beam as that of image 1 before doing the
combination.
Adverbs:
INNAME......First image name. Standard defaults.
INCLASS.....First image class. Standard defaults.
INSEQ.......First image seq. #. 0 => highest.
INDISK......Disk drive # for the first image. 0 => any.
IN2NAME.....Second image name. Standard defaults.
IN2CLASS....Second image class. Standard defaults.
IN2SEQ......Second image seq. #. 0 => highest.
IN2DISK.....Disk drive # for the second image. 0 => any.
IN3NAME.....First noise image name. Standard defaults.
IN3CLASS....First noise image class. Standard defaults.
IN3SEQ......First noise image seq. #. 0 => highest.
IN3DISK.....Disk # for first noise image. 0 => any.
IN4NAME.....Second noise image name. Standard defaults.
IN4CLASS....Second noise image class. Standard defaults.
IN4SEQ......Second noise image seq. #. 0 => highest.
IN4DISK.....Disk # for second noise image. 0 => any.
DOALIGN.....Controls how the four images are to be aligned (see HELP
DOALIGN). True (>.1) means that the images must agree in
their coordinates, though not necessarily in the reference
pixel position. Alignment is by coordinate values (if
DOALIGN > -0.1) or by offsets from the reference pixel
positions (if DOALIGN <= -0.1). NOTE: all real axes (>1
point) are aligned. If DOALIGN = -2, the headers are
ignored and the images are aligned at pixel (1,1,...).
OUTNAME.....Output image name. Standard defaults.
OUTCLASS....Output image class. Standard behavior with default =
either the output STOKES in string form or the OPCODE if
the output STOKES is the same as the first input image.
The noise image has the 6th character of class set to N.
OUTSEQ......Output image seq. #. 0 => highest unique.
OUTDISK.....Output disk number. 0 => highest with space.
BLC.........Bottom left corner of the 1st input image. The other
images are aligned by coordinates (see DOALIGN) on all
axes having > 1 point. The other images may have fewer
real axes than the 1st. The 4 windows must have the same
dimension on the first 2 axes, but the task will select a
smaller window than was specified if needed to overlap the
4 images.
TRC.........Top right corner of input images. (See BLC.)
OPCODE......The combination algorithm specification: (A=APARM)
='SUM ': Linear sum A(1)*MAP(1) + A(2)*MAP(2) + A(3)
If MAP(1) or MAP(2) is blank then
the output is blank
='DIV ': Division A(1)*MAP(1) / MAP(2) + A(2)
='SPIX': Sp. Index A(1)*SP.IND(MAP(1),MAP(2)) + A(2)
where MAP(1)>A(3)>=0 and MAP(2)>A(4)>=0
='POLI': Pol. Inten. A(1)*SQRT(MAP(1)**2 + MAP(2)**2))
+ A(2)
='POLC': Pol. Inten. A(1)*SQRT(MAP(1)**2 + MAP(2)**2))*C
+ A(2) where C = noise correction
='POLA': Pol. Angle A(1)*ATAN2(MAP(2),MAP(1)) + A(2)
where A(3) < SQRT (MAP(1)**2 + MAP(2)**2)
MAP(1)=QPOL, MAP(2)=UPOL usually.
='MULT': Multiplic. A(1)*MAP(1)*MAP(2) + A(2)
='OPTD': Opacity A(1) * LN (A(3)*MAP(1)/MAP(2)+A(4))
+ A(2)
where MAP(1) > A(5) and MAP(2) > A(6)
='CLIP': Clipping MAP(1) except where A(1) > MAP(2)
> A(2) or A(1) < A(2) and
either MAP(2) < A(1) or > A(2)
='REAL': Rect. conv. A(1)*(MAP(1)*COS(A(2)*MAP(2)) + A(3)
='IMAG': Rect. conv. A(1)*(MAP(1)*SIN(A(2)*MAP(2)) + A(3)
(MAP(2) assumed in degrees)
='MEAN': weighted mean AA(1)*MAP(1) + AA(2)*MAP(2)
AA(1) = A(1)/(A(1)+A(2))
AA(2) = A(2)/(A(1)+A(2))
IF (both MAP(1) and MAP(2) are blank) THEN
OUTPUT is blank
ELSE
IF (MAP(1) is blank) then OUTPUT = MAP(2)
IF (MAP(2) is blank) then OUTPUT = MAP(1)
='RM ': Rot. Meas. A(1)*(MAP(1)-MAP(2))/(Lam1^2-Lam2^2)/57.29578
+ A(2)
COMB tests angle diff +- 180,360 to bring
closer to A(3) (in degrees). Output RM is
in RADians/M/M when A(1)=1 (A(2) in
RAD/M/M). A(2) used also to bring angle
diff closer to A(3).
='SUMM': Linear sum A(1)*MAP(1) + A(2)*MAP(2) + A(3).
Almost identical to SUM, but different
treatment of blank points:
IF (both MAP(1) and MAP(2) are blank) THEN
OUTPUT is blank
ELSE
IF (MAP(1) is blank) then MAP(1) = 0
IF (MAP(2) is blank) then MAP(2) = 0
OUTPUT = A(1)*MAP(1) + A(2)*MAP(2) + A(3)
APARM.......Parameters needed for algorithm:
APARM(1), APARM(2), APARM(3), APARM(4) used as above.
APARM(1) = 0 => APARM(1) = 1.0 (except 'POLA','CLIP')
APARM(1) = 0 => APARM(1) = 28.648 (for 'POLA')
APARM(2) = 0 => APARM(2) = 1.0 (FOR 'SUM ')
APARM(3) = 0 => APARM(3) = 1.0 (for 'OPTD')
APARM(8) > 0 => Use 0.0 for clipped & illegal values
<= 0 => Use blanking for clipped & illegal values
APARM(9) = Clip if Abs (MAP(1)) < APARM(9) - image units.
APARM(10) = Clip if Abs(MAP(2)) < APARM(10) - image units.
There are no defaults for APARM(9) and (10) and a zero
value means no clipping. Used only if BPARM(4) <= 0.5
BPARM.......Parameters needed noise calculation and control:
BPARM(1) = 1-sigma level on 1st input map. < 0 => use third image
Zero is not allowed for 'POLC' and whenever BPARM(3) > 0
or BPARM(4) > 0.5.
BPARM(2) = 1-sigma level on 2nd input map. < 0 => use fourth image
Zero is not allowed for 'POLC' and whenever BPARM(3) > 0
or BPARM(4) > 0.5.
BPARM(3) = false (<= 0) => output normal image
= true (> 0) => output normal and sigma image
Blanking is the same for both settings of B(3).
BPARM(4) <= 0.5 => Blank output map using input map values
else => Blank output map using output map sigma
>= 1.5 => Blank output map using output map abs(S/N).
BPARM(5) = Error on output map value above which output
pixel is blanked (if BPARM(4) = 1) 0 -> ignore
= abs(S/N) ratio of output map value below which output
pixel is blanked (if BPARM(4) = 2) 0 -> ignore
BPARM(6) = Maximum value of sigma to be output (used if > 0 and
BPARM(3) > 0 only).
NOTE: certain combinations of BPARM(3), BPARM(4) and OPCODE do not
make much sense but all are allowed. S/N blanking may not be
desirable for POLI, SPIX and OPTD, for example. Output images
which are constant will be written and a warning message will
appear. The noise on RM images is determinable from the inputs
of COMB only when BPARM(1) = BPARM(2) = -1. Consider using task RM
for rotation measures since a 2-frequency RM computation is very,
very unreliable anyway.
In the descriptions above, the term FMAXn means
MAX( ABS(DATAMAX), ABS(DATAMIN) ) over the n'th map.
Task MATHS is used to do mathematical operations on single images.
The task POLCO performs the same operation as OPCODE 'POLC' with
a somewhat different algorithm for the correction.
DOHIST.......Normally the HI file of input 1 is copied to the output
history file and the HI file of the second input is
appended. If you are doing many COMBs this can lead to
immense history files of little use to anyone. Thus,
DOHIST=-2 => copy the first HI file only.
DOHIST=-3 => copy no HI file, write COMB HI only.
EXPLAIN SECTION