AIPS HELP file for IMMOD in 31DEC21
As of Sat May 15 15:45:33 2021
IMMOD: Task to alter map images.
INNAME Input image name (name).
INCLASS Input image name (class).
INSEQ 0.0 9999.0 Input image name (seq. #).
INDISK 0.0 9.0 Input image disk unit #.
OUTNAME Output image name (name).
OUTCLASS Output image name (class).
OUTSEQ -1.0 9999.0 Output image name (seq. #).
OUTDISK 0.0 9.0 Output image disk unit #.
BLC Bottom left corner of input.
TRC Top right corner of input.
OPCODE Model types are:
'GAUS', 'DISK', 'RECT',
'SPHE', 'EXPD', 'POIN'
NGAUS 1.0 4.0 Number components to add
FMAX Peak of component (Jy/beam)
FPOS -50.0 16434.0 (X,Y) position (pixels)
FWIDTH (BMAJ, BMIN, PA) of comp.
0->Use clean beam
FLUX Noise level
FACTOR Multiplication factor.
INLIST List of sources up to 9999
Use: Modification of existing map images by addition of models.
INNAME.....Input image name (name). Standard defaults.
INCLASS....Input image name (class). Standard defaults.
INSEQ......Input image name (seq. #). 0 => highest.
INDISK.....Disk drive # of input image. 0 => any.
OUTNAME....Output image name (name). Standard defaults.
OUTCLASS...Output image name (class). Standard defaults.
OUTSEQ.....Output image name (seq. #). 0 => highest unique.
OUTDISK....Disk drive # of output image. 0 => highest
number with sufficient space.
BLC........Bottom right corner in input image of desired
subimage. Default is entire image.
TRC........Top right corner in input image of desired
subimage. Default is entire image.
OPCODE.....Operation code to determine the type of model. Any
undefined OPCODE => Point. The available opcodes are
'POIN' => Point, 'GAUS' => Gaussian, 'DISK' => Solid Disk,
'RECT' => Solid Rectangle, 'SPHE' optically thin sphere,
'EXPD' => Exponential
NGAUSS.....The number of components in the model (1 - 4).
FMAX.......The peak value for each component. NO default.
FPOS.......The position (X,Y) for components. The values are in
pixels in the order (X1,Y1,X2,Y2,X3,Y3,X4,Y4).
FWIDTH.....The major axis, minor axis and position of major axis
for components. The values are pixels with degrees for
position angle and the order is
If the major or the minor are <= 0, then the Clean beam
FLUX.......Noise level to be added (in the units of the image)
FACTOR.....Factor by which the original data is multiplied
before it is added to the model. 0 => drop original
INLIST.....Set this blank unless you want an input components list.
Text file containing one line per source, giving
I, DX, DY, Maj, Min, PA
blank separated free format and trailing zeros may be
omitted. Used if INLIST not blank. The resulting NGAUS
will be #lines in INLIST neglecting comments (start with
# in col 1) and lines with format errors. Units are
Jy/beam, pixels, pixels, pixels, pixels, degrees. The
Clean beam is substituted if May and/or Min are 0 or
missing. Limit 9999. The model type specified by
OPCODE is used.
IMMOD: Task which modifies map images by scaling the existing
map and adding a specific model (See also UVMOD).
DOCUMENTOR: Eric R. Nelson NRAO/VLA/UNM
DATE OF DOCUMENTATION: 14 JUNE 1983
RELATED PROGRAMS: UVMOD, APCLN, UVMAP, COMB
IMMOD modifes an already existing map image by the addition of one
of four model types. The original map points may be scaled by a
multiplicative factor, including negative values and zero, before they
are added to the model. Random noise may also be added to the map. The
four available models to choose from are 1) point source, 2) Gaussian,
3) solid disk, 4) solid rectangle, 5) optically thin sphere, 6)
exponential disk.. The dimensions, offset and position angle are input
by the user.
The type model to be used can be selected by OPCODE. The
allowed models, and their corresponding OPCODEs are listed below.
1) Point -> 'POIN'
Only the specified point is altered. The position is
determined by FPOS. The criterion for the point selection is
Sqr(X^2 + Y^2) = 0
where (X,Y) is the current pixel location after correction for
any offset. Parameters BMAJ, BMIN and BPA have no affect on
this model. The value added is
ZEROSP(1) * CBarea / Cellx / Celly
where CBarea is the Clean beam area and Cellx and Celly are the
x and y cell sizes.
2) Gaussian -> 'GAUS'
ZEROSP(1) * (CBarea/NBarea) * EXP (-4Ln(2) * R**2)
is added to the map where
R = Sqrt(XX^2 + YY^2) with
XX = (Y*Cos(BPA) + X*Sin(BPA))/BMAJ
YY = (X*Cos(BPA) - Y*Sin(BPA))/BMIN
where X and Y are the same as above, but in units of arcsec.
NBarea is the new area defined by (1.1331 * BMAJ * BMIN)
3) Disk -> 'DISK'
A solid disk is added to the map. The amplitude is
ZEROSP(1) * BMarea / (Pi * BMAJ * BMIN / 4)
4) Rectangle -> 'RECT'
A solid rectangle is added to the map. The amplitude is
ZEROSP(1) * BMarea / (BMAJ * BMIN)
5) Sphere -> 'SPHE'
A circular function is added to the map:
ZEROSP(1) * BMarea / NBarea * sqrt (1-R*R)
R = sqrt (X*X + Y*Y) / BMAJ
NBarea = 2.094 *BMAJ * BMAJ
ZEROSP(1) * (CBarea/NBarea) * EXP (-2ln(2) * R)
is added to the map where R is defined above (in 2) and
NBarea = 3.2699 * BMAJ * BMAJ
BMAJ, BMIN, BPA (actually FWIDTH(1 through 3, i) for i'th component
The dimensions of the resulting functions are determined by BMAJ,
BMIN and BPA (position angle). For the Gaussian and exponential, the
first two numbers are the FWHM of the two axes. For the disk and
rectangle, the first two values are the absolute dimensions of the two
available axes. For the sphere, only BMAJ is used and it is the
diameter of the sphere.
If either BMAJ or BMIN is zero, then all the models reduce to the
The FACTOR term allows one to add a scaled version of original data
to the model. FACTOR is simply multiplied by the original data which is
then added to the model. If FACTOR = 0 then only a map of the model