AIPS HELP file for PATGN in 31DEC24
As of Fri Apr 19 22:38:43 2024
PATGN: Task to create a user specified test pattern.
INPUTS
IMSIZE Output image size (cells)
CELLSIZE Cellsize arc seconds.
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 #.
OPCODE Operation code. ZONE, GAUS,
LRTZ, RADI, POLY
BEAM, INVB
OPTYPE Array name: VLA, ATCA,
EVLA, JVLA, ' ' -> EVLA
CPARM Function parameters.
PBPARM Primary beam parameters
(1) Cutoff; (2) Use (3)-(7)
(3)-(7) Beam shape
HELP SECTION
PATGN
Task: Task which creates a user specified test pattern.
Adverbs:
IMSIZE.....Desired image size in cells. (default 256)
CELLSIZE...Desired cell spacing. (default 1.0)
OUTNAME....Output image name (name). Standard behavior with default =
'PATGN MAP'.
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.
OPCODE.....User specified operation code:
'ZONE' => Zone plate test pattern. This pattern is based
on a linearly swept FM signal. The intensity at each
point is given by:
|A*cos (2*PI*FMAX* RADIUS**2 / PERIOD)
| RADIUS <= PERIOD/2
f(RADIUS)=|
|A * cos (2*PI * FMAX * ((PERIOD/2)-
| (RADIUS-PERIOD)**2 / PERIOD)
| PERIOD/2 <= RADIUS <= 3*PERIOD/2
where A = amplitude (max/min intensity), FMAX = maximum
frequency (0<=FMAX<=0.5), RADIUS = distance from the
center point, PERIOD = number of pixels in the cycle
(from zero to FMAX and back to zero) and center =
CPARM(1,2), A = CPARM(3), PERIOD = CPARM(4), and FMAX =
CPARM(5). This pattern contains a wide variety of
frequency at all possible angles.
'GAUS' => Gaussian profile. This pattern is a
two-dimensional normal distribution with a specified
r.m.s. The intensity at each point is given by:
f(RADIUS) = C(3) + (C(4)-C(3)) *
EXP (-((0.707/C(5))**2*RADIUS**2))
where c = CPARM and 0.707/C(5) is the height of a
normal distribution with r.m.s.= C(5).
'LRTZ' => Lorentzian profile. This pattern is similar to
the Gaussian distribution. The intensity at each point
is given by:
f(RADIUS) = C(3) + (C(4)-C(3)) *
(1 / (1 + (RADIUS/C(5))**2))
'BEAM' => Do an image of the primary beam; by default,
the primary beam of the VLA.
'INVB' => Do an image of the 1.0/primary beam; by default,
the primary beam of the VLA.
'ATCA' => Do an image of the primary beam; by default, the
primary beam of the ATCA.
'RADI' => Do a polynomial in the radius from the
reference pixel
'POLY' => Do a polynomial in x and y (from the reference
pixel)
CPARM......CPARM(1) and CPARM(2) are the x and y pixel coordinates
of the function center, resp. If both are zero, center
set to (IMSIZE(1) + 1) / 2 and (IMSIZE(2) + 2) / 2.
If OPCODE is 'ZONE':
CPARM(3) is the amplitude of the signal (max/min
intensity, 0 => 1.0),
CPARM(4) is the period of the signal in arc seconds
(0 => 320*IMSIZE(1)/512 * CELLS(1)),
CPARM(5) is the maximum frequency of the signal
(ABS(CPARM(5)) > 0.5 => CPARM(5)=0.5).
If OPCODE is 'GAUS' or 'LRTZ':
CPARM(3) is the lower limit on the output
intensity (default 0.0),
CPARM(4) is the upper limit (default 1.0),
CPARM(5) is the width of the distribution in arc
seconds (0 => CELLS(1)/SQRT(2)). For 'GAUS' this
is the r.m.s. (the FWHM is 2.35482*CPARM(5)). For
'LRTZ' it is the Lorentz one-half width at one-half
maximum.
If OPCODE is 'BEAM':
CPARM(3) is the observing frequency in GHz; default
1.420
PBPARM(1) = value below which pattern is blanked (if 0
use the beam calculator's idea of "outside", so
set to < 0 to have no blanking)
PBPARM(2) is logical code: true (> 0) => use
BMPARM(3-7) to define the beam.
Otherwise use default parameters for the VLA (or
ATCA where appropriate)
For all wavelengths, the beam is described by the
function:
1.0 + X*PBPARM(3)/(10**3) + X*X*PBPARM(4)/(10**7) +
X*X*X*PBPARM(5)/(10**10) + X*X*X*X*PBPARM(6)/(10**13)
X*X*X*X*X*PBPARM(7)/(10**16)
where X is (distance from the pointing position in arc
minutes times the frequency in GHz)**2.
If OPCODE is 'ATCA':
CPARM(3) is the observing frequency in GHz; default
1.420
PBPARM(1) = value below which pattern is blanked (if 0
use the beam calculator's idea of "outside", so
set to < 0 to have no blanking)
PBPARM(2) is logical code: true (> 0) => use
BMPARM(3-7) to define the beam.
For all wavelengths, the beam is described by the
function:
1.0 + X*PBPARM(3)/(10**3) + X*X*PBPARM(4)/(10**7) +
X*X*X*PBPARM(5)/(10**10) + X*X*X*X*PBPARM(6)/(10**13)
X*X*X*X*X*PBPARM(7)/(10**16)
where X is (distance from the pointing position in arc
minutes times the frequency in GHz)**2.
If OPCODE is 'RADI':
The function is taken to be CPARM(3) + R*CPARM(4) +
R*R*CPARM(5) + R^3 * CPARM(6) + R^4 * CPARM(7) +
R^5 * CPARM(8) + R^6 * CPARM(9) + R^7 * CPARM(10)
where R is the radius in arc seconds.
If OPCODE is 'POLY':
The function is taken to be CPARM(3) + X*CPARM(4) +
Y*CPARM(5) + X^2 * CPARM(6) + Y^2 * CPARM(7) +
X^3 * CPARM(8) + Y^3 * CPARM(9) + X^4 * CPARM(10) +
Y^4 * PBPARM(1) + X*Y * PBPARM(2) +
X*X*Y * PBPARM(3) + X*Y*Y * PRPARM(4) +
(X^3)*Y * PBPARM(5) + (Y^3)*X * PBPARM(6) +
(X*Y)^2 * PBPARM(7)
where X and Y are the signed distance from the
reference pixel in arc seconds in the x and y axis.
EXPLAIN SECTION
PATGN: Task which creates a user specified test pattern.
DOCUMENTOR: Thad A. Polk, NRAO.
RELATED PORGRAMS: AIPS, All AIPS image tasks.
PURPOSE
PATGN is designed to produce a variety of test patterns
for use in image processing tasks. It generates regular or
symmetric images which can be tailored to the users needs. In
particular, the patterns can be used to test the response of
various processing algorithms. The necessary control
information can be passed to the program via OPCODE and CPARM.
For information about compiling, link-editing, and running PATGN
see HELP NEWTASK or the AIPS programmers' manual.
DETAILS ABOUT SPECIFIC OPCODES
GAUS: this is the Gaussian profile. With this OPCODE, the user
can produce an image based on a normal distribution of
specified width. These images could be used in a variety
of ways. For example, one could convolve the test
pattern with other images to blur them, or simply to test
the convolution algorithm.
LRTZ: this is the Lorentzian profile. It is similar to the
Gaussian profile except that the peak is less sharp, with
the tails of the distribution being wider. Its uses are
similar to those described for the Gaussian profile.
ZONE: this is the Zone Plate pattern. It produces an image that
is circularly symmetric with dark and light bands
alternating. The bands are wide at the refernce point,
get thinner until the distance from the reference point
is half the specified period and then get wider again.
This pattern produces a wide variety of frequencies
(alternation of light and dark) at all possible angles
and is thus very useful in testing the frequency response
of various processing algorithms. For example, one could
run the pattern through an algorithm, run the result
through an inverse operation and compare final picture
with the original and determine what sort of artifacts
the algorithm produces and at what angle and frequency
these artifacts tend to appear.
BEAM: PRIMARY BEAM CORRECTION
INVB
PATGN corrects an image for the primary beam attenuation of
the antennas. The function used to model the primary beam for normal
VLA frequencies
F(x) = 1.0
+ parm(3) * 10E-3 * x
+ parm(4) * 10E-7 * x*x
+ parm(5) * 10E-10 * x*x*x
+ parm(6) * 10E-13 * x*x*x*x
+ parm(7) * 10E-16 * x*x*x*x*x
where x is proportional to the square of the distance from the
pointing position in units of [arcmin * freq (GHz)]**2, and F(x)
is the multiplicative factor to divide into the image intensity at the
distance parameter x. For other antennas, the user may read
in appropraite constants in PBPARM(3) through PBPARM(7). The
flag, PBPARM(2) must be set to a positive number to invoke this
option and PBPARM(3) must not be zero.
This correction scales with frequency and has a cutoff
beyond which the map values are set to an undefined pixel value GIVEN
in PBPARM(1). At the VLA frequencies the default cutoff is
1.485 GHz 29.8 arcmin
4.885 GHz 9.13 arcmin
15 GHz 2.95 arcmin
22.5 GHz 1.97 arcmin
and occurs at a primary beam sensitivity of 2.3 percent of the value at
the beam center. Corrections factors < 1 are forced to be 1.
The estimated error of the algorithm is about 0.02 in (1/F(x))
and thus leads to very large errors for x>1500, or at areas
outside of the primary response of 20 percent. The cutoff level
may be specified with DPARM(1).
Default values of PBPARM for the VLA are given by Perley's fits:
0.0738 GHz -0.897 2.71 -0.242
0.3275 -0.935 3.23 -0.378
1.465 -1.343 6.579 -1.186
4.885 -1.372 6.940 -1.309
8.435 -1.306 6.253 -1.100
14.965 -1.305 6.155 -1.030
22.485 -1.417 7.332 -1.352
43.315 -1.321 6.185 -0.983
For the ATCA, these are by default:
1.5 GHz -1.049 4.238 -0.8473 0.09073 -5.004E-3
2.35 -0.9942 3.932 -0.7772 0.08239 -4.429E-3
5.5 -1.075 4.651 -1.035 0.12274 -6.125E-3
8.6 -0.9778 3.875 -0.8068 0.09414 -5.841E-3
20.5 -0.9579 3.228 -0.3807 0.0 0.0
For the Karl G Jansky VLA ("EVLA"), the defaults are frequency
dependent. If the observing frequency is between two tabulated
frequencies, then the beam is computed for each of the tabulated
frequencies and then interpolated to the observing frequency. The
values used are far too numerous to give here, see EVLA Memo 195,
"Jansky Very Large Array Primary Beam Characteristics" by Rick Perley,
revision dated June 2016. Obtain it from
http://library.nrao.edu/evla.shtml
RICK PERLEY'S (OLD) REPORT
Polynomial Coefficients from LSq Fit to VLA Primary
Beam raster scans.
Functional form fitted:
1 + G1.X^2 + G2.X^4 + G3.X^6
where X = r.F,
and r = radius in arcminutes
F = frequency in GHz.
Fits were made to 3 percent cutoff in power for 24 antennas.
Poor fits, and discrepant fits were discarded, and the most
consistent subset of antennas had their fitted coefficients
averaged to produce the following 'best' coefficients.
Freq. G1 G2 G3
0.0738 -0.897E-3 2.71 E-7 -0.242E-10
0.3275 -0.935 3.23 -0.378
1.285 -1.329 6.445 -1.146 *
1.465 -1.343 6.579 -1.186
4.885 -1.372 6.940 -1.309
8.435 -1.306 6.253 -1.100
14.965 -1.305 6.155 -1.030
22.485 (old) -1.350 6.526 -1.090 *
22.485 (new) -1.417 7.332 -1.352
43.315 -1.321 6.185 -0.983
The estimated errors (from the scatter in the fitted
coefficients) are generally very small:
G1: .003 at all bands except Q (.014)
G2: .03 to .07 at all bands except Q (.15)
G3: .01 to .02 at all bands except Q (.04)
R. Perley 21/Nov/00
* The 1.285 and 22.485 old feed values are not used.