AIPS HELP file for MODIM in 31DEC21
As of Fri Sep 17 13:01:34 2021
MODIM: Task to alter I, Q, U images adding models
INNAME Input I image name (name).
INCLASS Input I image name (class).
INSEQ 0.0 9999.0 Input I image name (seq. #).
INDISK 0.0 9.0 Input I image disk unit #.
IN2NAME Input Q image name (name).
IN2CLASS Input Q image name (class).
IN2SEQ 0.0 9999.0 Input Q image name (seq. #).
IN2DISK 0.0 9.0 Input Q image disk unit #.
IN3NAME Input U image name (name).
IN3CLASS Input U image name (class).
IN3SEQ 0.0 9999.0 Input U image name (seq. #).
IN3DISK 0.0 9.0 Input U image disk unit #.
OUTNAME Output image name (name).
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.
FLUX Noise level to add
FACTOR Multiplication factor.
OPCODE Model types are:
'GAUS', 'DISK', 'RECT',
'SPHE', 'EXPD', 'POIN'
OPTYPE 'SLAB', 'GAUS', 'EXP '
INLIST List of sources up to 9999
New image parameters:
COORDINA Ra, Dec coordinates
IMSIZE Ra, Dec number of pixels
CELLSIZE Ra, Dec increments in asec
APARM (1) Frequency (GHz) plane 1
(2) increment (GHz)
(3) number channels
Use: This task can be used to modify a trio of existing image cubes of
I, Q, and U polarization or create new ones.
INNAME.....Input I image name (name). No default.
INCLASS....Input I image name (class). Standard defaults.
INSEQ......Input I image name (seq. #). 0 => highest.
INDISK.....Disk drive # of input I image. 0 => any.
IN2NAME....Input Q image name (name). No default.
IN2CLASS...Input Q image name (class). Standard defaults.
IN2SEQ.....Input Q image name (seq. #). 0 => highest.
IN3DISK....Disk drive # of input Q image. 0 => any.
IN3NAME....Input U image name (name). No default.
IN3CLASS...Input U image name (class). Standard defaults.
IN3SEQ.....Input U image name (seq. #). 0 => highest.
IN2DISK....Disk drive # of input U image. 0 => any.
OUTNAME....Output image name (name). Standard defaults.
Outclasses are IMODEL, QMODEL, and UMODEL
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.
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
OPCODE.....Operation code to determine the type of model. Any
undefined OPCODE => Gaussian. The available opcodes are
'POIN' => Point, 'GAUS' => Gaussian, 'DISK' => Solid Disk,
'RECT' => Solid Rectangle, 'SPHE' optically thin sphere,
'EXPD' => Exponential
OPTYPE.....The thickness is applied with a function specified by:
'SLAB' - sin(x)/x with x = beta * lambda^2
'GAUS' - exp(-f * x * x) with f = ln(2) / (1.8954)^2
'EXP ' - exp(-f * abs(x)) with f = ln(2) / 1.8954
(Note 1.8954 radians is the point where sin(x)/x = 0.5
and beta is called RMthick below in radians/m/m)
INLIST.....Text file containing one line per source, giving
I, Q, U, Spix, RM, RMthick, DX, DY, Maj, Min, PA, Type#
blank separated free format and trailing zeros may be
omitted. I, Q, and U are those that would be measured at
1 GHz wavelength. The resulting number of components
will be the number of lines in INLIST neglecting comments
(which start with # in col 1) and lines with format
errors. Units are Jy/beam, Jy/beam, Jy/beam, unitless,
radians/m^2, radians/m^2, pixels, pixels, pixels, pixels,
degrees, and unitless. Types are point, Gaussian,
uniform disk, uniform rectangle, optically thin sphere,
and exponential for code numbers 1 through 6. Default
value for code is the code selected by OPCODE.
The Clean beam is substituted if Maj and/or Min are 0 or
missing. Limit 9999. If all of Q and U are zero then
only I polarization is done.
If making a new image (INNAME blank with I polarization or
INNAME and/or IN2NAME and/or IN3NAME blank with I, Q, U) use
COORDINA...RA (hours minutes seconds of time), declination (degrees,
minutes, seconds of arc) for reference pixel (at image
IMSIZE.....X, Y image size in pixels
CELLSIZE...X, Y image spacing in arc sec
APARM......(1) Reference frequency at first output plane in GHz
(2) Increment in frequency in GHz
(3) Number of frequency pixels
MODIM: 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