AIPS HELP file for RMFIT in 31DEC18
As of Tue Jan 16 9:50:51 2018
RMFIT: Fits polarization spectrum to Q/U cubes.
INNAME Input Q image name (name)
INCLASS Input Q image name (class)
INSEQ 0.0 9999.0 Input Q image name (seq. #)
INDISK 0.0 9.0 Input Q image disk unit #
INVERS 0.0 RM table version number
IN2NAME Input U image name (name)
IN2CLASS Input U image name (class)
IN2SEQ 0.0 9999.0 Input U image name (seq. #)
IN2DISK 0.0 9.0 Input U image disk unit #
IN3NAME Input I image name (name)
IN3CLASS Input I image name (class)
IN3SEQ 0.0 9999.0 Input I image name (seq. #)
IN3DISK 0.0 9.0 Input I image disk unit #
IN4NAME FARS real image name (name)
IN4CLASS FARS real image name (class)
IN4SEQ 0.0 9999.0 FARS real image name (seq. #)
IN4DISK 0.0 9.0 FARS real image disk unit #
IN5NAME FARS imag image name (name)
IN5CLASS FARS imag image name (class)
IN5SEQ 0.0 9999.0 FARS imag image name (seq. #)
IN5DISK 0.0 9.0 FARS imag 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
YINC 0.0 128.0 Do every YINCth row
ZINC 0.0 128.0 Do every ZINCth plane
PCUT 0.0 Flux cutoff in total
ICUT 0.0 Flux cutoff in unpolarized I
DOOUTPUT -1.0 3.0 Write residual image: 1,3
write parameter img: 2,3
NITER 0.0 4000.0 Max # fit iterations
0 -> 100.
NGAUSS 1.0 4.0 Max number components
DOTV 1.0 2.0 TV is always used
2 => TV for questions too
DOSPIX -1.0 4.0 1 => fit spectral index
2,3,4 => fit thickness
else keep both at zero
RMSLIMIT Switch from automatic to
interactive if rms > RMSLIMIT
DOWEIGHT -1.0 2.0 > 0 weighted solution
> 1.5 RMFIT finds weights
INFILE Text file with weights
BADDISK Disk to avoid for scratch
Task: Fits polarization spectra for one or more components of total
polarization, polarization angle at 0 wavelength, and rotation
measure. RMFIT will be used on Q and U image cubes with
frequency or frequency ID as the first axis and latitude and
longitude as the second and third axes. It requires the real
and imaginary or amplitude and phase images output by FARS,
with rotation measure as the first axis and latitude and
longitude as axes 2 and 3. It also requires an image of I
polarization which can be a corresponding transposed cube or a
single latitude/longitude plane. All images must have the same
coordinates in all corresponding axes or the results will be
The task fits up to 4 polarization components to each spatial
pixel. Optionally, it writes up to 10*NGAUSS n-1 dimensional
images containing the fit parameters and their uncertainties
and/or the residual image. An interactive mode (using the TV
graphics planes) is required. With NGAUS = 1, it is often
possible to turn off the interactivity for large parts of the
fitting if it is going well. The interactivity will be turned
back on automatically if the answers are obviously wrong. Note
that, since the TV is not allowed in BATCH jobs, RMFIT may not
be run in BATCH.
Color differentiates what is plotted. Graphics channel 1
(usually yellow) is used for axis labels and the data. The
FARS output is plotted in amplitude/phase initially. The
initial guess is shown as a large X in graphics channel 2
(usually green). This screen may be used to reset the initial
guess. Then the Q and U data are plotted. Since the Q and U
data may be on a FQID axis and so may not actually be in
frequency order, the Q and U data are plotted as small X's.
The initial guess is shown as a smooth curve in graphics
channel 2 (usually green). The fit is then shown as somewhat
large X's in graphics channel 4 (usually cyan).
RMFIT started with the transformed XGAUS to be the task it
should be. When run in interactive mode, no output files are
created except for a large table file used to hold the results
of the fitting (an RM file). The table is initialized with
pixel positions and fluxes before any fitting is done. Then
the fitting is done sequentially through the input cube. After
that, in interactive mode, a menu-driven routine is brought up
to allow you to review the fits including re-doing poor ones,
rearranging the numbering of the components, and other editing
of the results. Finally output files are written if requested.
RMFIT may be re-started using the RM file either resuming the
sequential fitting (if it was not completed) or dropping into
the edit stage directly. The RM file is created with the full
pixel ranges of the input axes 2 and 3. You may then use a
limited BLC(2,3)-TRC(2,3) in the initial fitting and the same
or different ranges when re-starting. This is helpful to fit a
single region with similar polarization at each execution. The
output images will cover the entire range of the input images.
Note that BLC(1)-TRC(1) always controls which spectral channels
are examined and thus the peak total and polarizaed intensities
in the RM table. Thus the first execution should probably
cover all useful spectral channels. Also it would be a bad
idea to change BLC and TRC (4,5,6,7). Note too that the
various sessions are allowed to use different values of NGAUS.
The table routines always handle 4 components, but it is much
easier to provide guesses for a smaller number of components
whose values will be then stored in the low numbered
components. In the edit stage, you could specify a larger
number of components and move some of these low numbered
solutions into higher numbers.
Details of the interactive operation and options are described
in the EXPLAIN file. See also AIPS Memo 118, "Modeling
spectral cubes in AIPS", January 2016 for a more detailed
description of the use of this task.
The model fit is:
Q(i) = SUM_j [ P_j cos ( 2 theta_j + 2 RM_j lambda(i)^2
F (beta_j, lambda(i)^2) ]
U(i) = SUM_j [ P_j sin ( 2 theta_j + 2 RM_j lambda(i)^2
F (beta_j, lambda(i)^2) ]
where P_j is the polarized flux at 1 GHz, theta_j is the
intrinsic polarization angle, and RM_j is the rotation measure
in radians/m/m. F(beta_j, lambda(i)^2) is an amplitude
function that solves for a spectral index or one of several
possible thickness parameters. The spectral index function
(lambda_1^2 / lambda(i)^2)^(beta_j/2)
while the thickness functions are ('SLAB' in MODIM) and ('GAUS'
in MODIM) and ('EXP ' in MODIM)
sin (beta_j lambda(i)^2) / (beta_j lambda(i)^2)
exp (-ln(2) * (beta_j lambda(i)^2 / 1.8954)^2)
exp (-ln(2) * beta_j lambda(i)^2 / 1.8954)
where lambda_1 is the wavelength at 1 GHz and beta_j is the
spectral index or the thickness parameter, the latter in
rad/m/m. Set DOSPIX to 1 for spectral index or 2,3,4 for SLAB,
GAUS, or EXP. respectively. The 1.8954 was chosen to make all
functions have the same half-power point. Output images are
written of the P_j, theta_j, RM_j, beta_j, Q0_j, and U0_j and
their uncertainties, where
Q0_j = P_j cos ( 2 theta_j )
U0_j = P_j sin ( 2 theta_j )
are Q and U at 1 GHz without rotation measure. The beta_j
images are only written when they have been fit.
INNAME.....Input Q image name (name). Standard defaults.
INCLASS....Input Q image name (class). Standard defaults.
INSEQ......Input Q image name (seq. #). 0 => highest.
INDISK.....Disk drive # of input Q image. 0 => any.
INVERS.....Input RM table version. 0 => a new one. Set this adverb
if you wish to re-start a fitting session.
IN2NAME....Input U image name (name). Standard defaults.
IN2CLASS...Input U image name (class). Standard defaults.
IN2SEQ.....Input U image name (seq. #). 0 => highest.
IN2DISK....Disk drive # of input U image. 0 => any.
The I image may either be a transposed cube matching the
Q and U cubes, or it may be a single plane with the
latitude/longitude axes 1 and 2 matching the
latitude/longitude axes 2/3 of the Q, U, real, and
imaginary cubes. IN3NAME and IN3CLASS both blank means
to ignore the test on I entirely.
IN3NAME....Input I image name (name). Standard defaults.
IN3CLASS...Input I image name (class). Standard defaults.
IN3SEQ.....Input I image name (seq. #). 0 => highest.
IN3DISK....Disk drive # of input I image. 0 => any.
IN4NAME....Input FARS real/amplitude image name (name).
IN4CLASS...Input FARS real/amplitude image name (class).
IN4SEQ.....Input FARS real/amplitude image name (seq. #).
0 => highest.
IN4DISK....Disk drive # of input FARS real/amplitude image.
0 => any.
IN5NAME....Input FARS imaginary/phase image name (name).
IN5CLASS...Input FARS imaginary/phase image name (class).
IN5SEQ.....Input FARS imaginary/phase image name (seq. #).
0 => highest.
IN5DISK....Disk drive # of input FARS imaginary/phase image.
0 => any.
OUTNAME....Output image name (name). Standard defaults.
OUTCLASS is set for each image by the task:
QRESID, URESID, PPOLn, THETAn, ROTMEn, Q0_n,
U_n, DPPOLn, DTHETn, DROTMn, DQ0_n, DU0_n
for n = 1 to NGAUS.
OUTSEQ.....Output image name (seq. #). 0 => highest unique.
OUTDISK....Disk drive # of output image. 0 => highest number with
BLC........Bottom right corner in input image of desired subimage.
(1) controls which spectral channels are used. The RM
table always contains all pixels in axes 2 and 3 so
BLC(2,3)-TRC(2,3) simply restricts the search range for
the current execution.
TRC........Top right corner in input image of desired sub-image for
the current fitting. Default is entire image.
YINC.......Do initially every YINC'th row (beginning at BLC(2)).
All rows will be done in the second stage.
ZINC.......Do initially every ZINC'th plane (beginning at BLC(3)).
All planes will be done in the second stage.
PCUT.......A polarized flux cutoff in the same units as the input
image (i.e. Jy/beam). If a row does not have an average
polarized flux above this level, no component is fit to
the row. It is also used to limit the points which
determine the initial guess. If you do a re-start with a
new lower value of PCUT, RMFIT will go into a special
sequential mode to fit all rows with values between the
previous and new PCUT levels.
ICUT.......A total intensity flux cutoff in the same units as the
input image (i.e. Jy/beam). If a celestial-coordinate
pixel does not have an average total intensity flux above
this level, no component is fit to the pixel. If you do
a re-start with a new lower value of ICUT, RMFIT will go
into a special sequential mode to fit all rows with
values between the previous and new ICUT levels.
DOOUTPUT...= 1 or 3 requests that the residual (data-model) images
be written out as cataloged images
= 2 or 3 requests that the model is written out as
Note that DOOUTPUT can be changed interactively during
the imaging portion of the task and the value of the
adverb at exit is all that matters.
NITER......Maximum function evaluations during the fit of each row.
(< 10 -> 100 for NGAUSS > 1, < 100 -> 150 for 1
NGAUSS.....Number of Components to fit (between 1 and 4).
DOTV.......= 1 => use TV (required!)
= 2 => also use TV for questions
DOSPIX.....If 0.5 < DOSPIX < 1.5, solve for spectral index in the
corresponding component, otherwise take the spectral
index to be zero.
If 1.5 < DOSPIX < 2.5, solve for the thickness parameter
in the corresponding component with sin(x)/x form, or,
if 2.5 < DOSPIX < 3.5, solve for the thickness parameter
in the corresponding component with Gaussian form, or,
if 3.5 < DOSPIX < 4.5, solve for the thickness parameter
in the corresponding component with Exponential form.
Otherwise take the thickness parameter to be zero.
NOTE: all values of DOSPIX must be either 0 or indicate
the same functional form.
RMSLIMIT...When the fitting has been told to continue without the
TV, switch interactive mode back on whenever the Q
and/or U rms exceeds RMSLIMIT. 0 -> 1000000.
DOWEIGHT...> 0 => Do a weighted solution. If INFILE is not blank,
and DOWEIGHT < 1.5, read the weights from INFILE.
Otherwise compute the weights from the rms of each
image plane found through robust methods.
<= 0 => Use all weights = 1.
INFILE.....Text file containing the weights, like the file in FARS
but allowing weights of any positive value (not just
integers from 1 to 99). Note that RMFIT expects a weight
for every pixel on the first axis of INNAME but uses only
those numbered BLC(1) through TRC(1). If there are more
weights than the total number of pixels on the first
axis, then the second half of the file is assumed to be
for U weights. Any Q weight <= 0 is replaced with 1.0.
Any U weight <= 0 is replaced with the corresponding Q
weight. Weights may have any positive value, not just
integers and more than one value may appear on each line
of INFILE. If a line contains a semi-colon, then the
content of the line from the semi-colon to the end is
treated as a comment. Note that the weights actually
used are scaled so that their sum is 2N where N is the
number of spectral channels used in the fit. They are
recorded in the history file of the output images.
BADDISK....Disk drives to avoid for scratch files.
IMAGR: One-dimensional polarization fitting of image cubes
Documenter: E. W. Greisen NRAO
Related Programs: IMFIT, JMFIT, SAD, SLFIT, ZEMAN, XGAUS
RMFIT is a new task in 31DEC13 based on the overhauled Gaussian task
XGAUS. At present, RMFIT assumes that there are at most 3 axes with
more than one pixel in the input images.
RMFIT begins by making an RM table containing one row for every pixel
in the output plane ignoring BLC and TRC. Each row of the table
is initialized with the average value of total polarization and total
intensity for each output (spatial) pixel. Within the window
specified by BLC(2)-TRC(2) and BLC(3)-TRC(3), RMFIT begins fitting
those rows having average values above PCUT and ICUT, doing every YINC
pixel in the Y axis and ZINC pixel in the Z axis. Initial guesses for
each fit are found from the FARS output data. When NGAUSS = 1 this
can happen automatically from the row data or it can come from a
previous fit for NGAUSS > 1. After each input image row (output
pixel) is fit, the results are added to the RM table immediately.
This allows the interactive user to quit at any time and then restart
the process later (set INVERS to point at the pre-existing RM table
which you intend to modify). After the YINC by ZINC pass through the
data, a second pass through the data is done on every output pixel.
Those pixels which have already been fit are skipped, but the results
from them contribute to the next initial guess.
Finally, when all pixels have been fit, RMFIT enters an interactive
routine designed to improve the results before any output images are
written. However, before describing that function, we need to provide
details of the interactive fitting of each row of the input image.
This process is followed whenever a row is fit in the first YINC/ZINC
function, in the second every pixel function, and in the third result
For each spectrum, the first step in the fitting process is to
determine an initial guess non-interactively. If RMFIT is currently
in interactive mode, the next steps are:
1. The input FARS output data are plotted on the TV as amplitude
and phase. The initial guess is added to the plot of the data
as a large X in both the amplitude and phase portions of the
2. If either NGAUSS > 1 or a fitting has been forced, RMFIT asks
in a TV menu (DOTV=2) or in the AIPS window for instructions.
If your answer begins with E or e (RE-GUESS on the TV), RMFIT
will ask you to enter a new initial guess step 3). If the
answer begins with B or b (BAD on TV), RMFIT will mark this
pixel as bad and, if the answer begins with Q or q (QUIT on the
TV), RMFIT will simply exit, allowing you to restart it at a
later time. If the answer is anything else, e.g. a simple
carriage return ("Enter") or DO FIT on the TV, RMFIT goes on to
step 4 below.
3. To enter a new initial guess, you will be prompted to position
the TV cursor at the rotation measure of each Component (note
that only the X position matters). To mark each point, hit any
button (A, B, C, or D). RMFIT then returns to step 1 above to
plot the new guess and ask again.
4. Once an acceptable initial guess has been found, RMFIT proceeds
to call a non-linear least squares fitting routine to determine
the polarization parameters that appear to fit the data best.
The answers are then checked to see if they are "reasonable" -
negative and very large components and components with rotation
measures outside the input data are unreasonable.
5. If the result is unreasonable and the current mode is not
interactive, the interactive mode is turned back on (with a
message and a display of the answers in the message terminal
window) and RMFIT returns to step 1.
6. If the current mode is interactive, the final model is added to
the plot. In the input terminal, you are then told if the
answers are "unreasonable" and are shown the answers,
reasonable or not. You are then offered a variety of choices.
If your response begins with:
a) B or b - the solution is marked as bad and RMFIT goes on
to the next input row (BAD on the TV)
b) Q or q - RMFIT exits cleanly, leaving the RM table to be
worked on again at a later time (QUIT on the TV)
c) R or r - RMFIT returns to step 1 to try again with the
current number of components (<= NGAUSS)
(RE-GUESS on the TV)
c) E or e - RMFIT returns to step 1 to try again with the
current number of components (<= NGAUSS)
(RE-GUESS on the TV)
e) 1, 2, 3, or 4 - RMFIT returns to step 1 to try again with
the specified number of Components (note that
only numbers <= NGAUSS are respected)
(1, 2, 3, and 4 on the TV as needed)
f) H or h - RMFIT prompts you to enter the polarization
parameters for each component (HAND on the TV).
You enter in the input terminal window, the
total polarization in input image units, the
polarization position angle at zero wavelength
in degrees (-90 to +90), the rotation measure in
radians per meter squared and, if appropriate,
the spectral index (unitless) or RM thickness
(radians per meter squared). All 3 or 4 numbers
must appear in one line. It will prompt for all
NGAUSS components, but will change the prompt if
the current number of Components is < NGAUSS.
If you enter something besides 0 in that case,
the the current number of Components is
increased appropriately. RMFIT then returns to
the start of this step 6 to allow you to see if
you made a good guess.
g) D or d - After a HAND operation, a DO FIT option is
available. It loops back using the hand-entered
parameters as the initial guess to the fitting
h) T or t - RMFIT turns off the interactive mode and does
solutions in a batch-like fashion until an
unreasonable solution is found or it finishes
the current function (TVOFF on the TV)
i) P or p - RMFIT prompts you for the Q and U display ranges
to re-display the data (PIXRANGE on the TV).
Enter Qmin, Qmax, Umin, Umax in that order in
one line. If you enter only two values, then
Umin and Umax are taken to equal Qmin and Qmax.
If you enter no values, then the plot reverts to
self-scaling. The Q plot self-scales if Qmin >=
Qmax; the U plot self-scales if Umin >= Umax.
Note that on the re-plot, the smooth "initial
guess" line is now actually the result of the
j) S or s - RMFIT will switch the display between Q plus U
and total polarization and polarization angle.
The plotted "initial guess" becomes the actual
fit results. (SHOW P&A or SHOW Q&U on the TV
k) Anything else - RMFIT saves the answer (with
uncertainties) and goes on to the next input
spectrum (GOOD on the TV).
Note, on retries (R, E, 1, 2, 3, and 4), step 2 will skip the
questions and go on to step 3 directly (as if you had answered
After all pixels that are strong enough have been given a solution,
RMFIT enters a menu-driven function. The menu has in the left column:
| EXIT | Exit RMFIT, writing output images if DOOUTPUT
is now > 0.
| SET MIN S/N | Set minimum total polarization S/N(s) for okay
| SET MIN P1 | Set minimum polarization for okay solutions
| SET MAX RESID | Set maximum residual for okay solutions
| SET RM RANGE | Set rotation measure range(s) for okay solutions
| SET MAX THETA ER | Set maximum error(s) in polarization angle for
| SET SPIX RANGE | Set range of spectral index(s) for okay
| SET THICKNESS MAX | Set maximum thickness parameter(s) for okay
| REDO ALL | Re-do all solutions which are not okay
| FLAG ALL | Mark bad all solutions which are not okay
| OFF ZOOM | Turn of TV zoom
| OFF TRANSFER | Turn off black & white and color TV enhancements
| SET DOOUTPUT | Increment DOOUTPUT in loop 0-3 - with 1 and 3
causing residual images and 2 and 3 causing
parameter images to be written on EXIT
| ADD TO LIST | Type in output pixel coordinates to add to list
| SHOW LIST | Display coordinates in list
| REDO LIST | Re-do solutions for all pixels in list
| FLAG LIST | Flag solutions for all pixels in list
| SWAP LIST 1-2 | Swap solutions for components 1 and 2 for all
pixels in list
| SWAP LIST 1-3 | Swap solutions for components 1 and 3 for all
pixels in list
| SWAP LIST 2-3 | Swap solutions for components 2 and 3 for all
pixels in list
| SWAP LIST 1-4 | Swap solutions for components 1 and 4 for all
pixels in list
| SWAP LIST 2-4 | Swap solutions for components 2 and 4 for all
pixels in list
| SWAP LIST 3-4 | Swap solutions for components 3 and 4 for all
pixels in list
Only appropriate SWAP LIST options are actually displayed. Also the
SPIX RANGE and THICKNESS MAX are only displayed as appropriate.
Three editing concepts are present in this menu. The first is to
establish what parameter values (S/N in peak, polarization, peak
residual, rotation measures, and error in polarization angle) for each
component constitute an "okay" solution. The selected limits are
displayed above the menu. Then you can choose to try to REDO ALL
solutions which are not okay or simply FLAG ALL, marking them as bad.
The second concept is to create a list of up to 1000 output pixels
which are thought to have some problem. You can enter these pixels by
hand (or remove pixels from the list by hand) with ADD TO LIST. A
faster way to add to the list is to show the image of some parameter
and then select interesting pixels while doing CURVALUE (see below).
The list of pixels can be re-done (REDO LIST) or marked as bad (FLAG
LIST). The list is cleared by these operations so you can make a new
list as needed. The third editing method available here is to take
the pixel list and swap the solutions at those pixels between
component N with component M.
The right hand column of options include:
| SHOW IMAGE P0_1 | Enter image interaction with total polarization
value of component 1
| SHOW IMAGE TH_1 | Enter image interaction with polarization angle
of component 1
| SHOW IMAGE RM_1 | Enter image interaction with rotation measure
of component 1
| SHOW IMAGE SP_1 | Enter image interaction with spectral index
of component 1
| SHOW IMAGE BE_1 | Enter image interaction with rotation measure
thickness ("beta") of component 1
| SHOW IMAGE Q0_1 | Enter image interaction with Q polarization at
wavelength 0 of component 1
| SHOW IMAGE U0_1 | Enter image interaction with U polarization at
wavelength 0 of component 1
| SHOW IMAGE EP0_1 | Enter image interaction with uncertainty in
total polarization of component 1
| SHOW IMAGE ETH_1 | Enter image interaction with uncertainty in
polarization angle of component 1
| SHOW IMAGE ERM_1 | Enter image interaction with uncertainty in
rotation measure of component 1
| SHOW IMAGE ESP_1 | Enter image interaction with uncertainty in
spectral index of component 1
| SHOW IMAGE EBE_1 | Enter image interaction with uncertainty in
rotation measure thickness ("beta") of
| SHOW IMAGE EQ0_1 | Enter image interaction with uncertainty in
Q polarization at wavelength 0 of component 1
| SHOW IMAGE EU0_1 | Enter image interaction with uncertainty in
U polarization at wavelength 0 of component 1
The SP and BE options are only shown when appropriate. For NGAUSS >
1, appropriate additional choices are offered.
When you select one of the above options, the above menus are turned
off, the image plane maintained in memory is displayed on the TV
screen, and a new menu is displayed. If offers:
| RETURN | Return to the above menus, image stays displayed
| LOAD AS SQ | Re-load image with square root transfer function
| LOAD AS LG | Re-load image with log transfer function
| LOAD AS L2 | Re-load image with extreme log transfer function
| LOAD AS LN | Re-load image with linear transfer function
| SET WINDOW | Set a sub-image to view
| RESET WINDOW | Return to viewing the full image
| OFF TRANSF | Turn off enhancement done with TVTRANSF
| OFF COLOR | Turn off color enhancements
| TVTRANSF | Black & white image enhancement
| TVPSEUDO | Color enhancement of numerous sorts
| TVPHLAME | Color enhancement of flame type, multiple colors
| TVZOOM | Interactive zooming and centering of image
| CURVALUE | Display value under cursor, mark pixels for list
| SWAP 1-2 | Swap solutions for components 1 and 2 interactively
| SWAP 1-3 | Swap solutions for components 1 and 3 interactively
| SWAP 2-3 | Swap solutions for components 2 and 3 interactively
| SWAP 1-4 | Swap solutions for components 1 and 4 interactively
| SWAP 2-4 | Swap solutions for components 2 and 4 interactively
| SWAP 3-4 | Swap solutions for components 3 and 4 interactively
| NEXT WINDOW | Move to next window into large images
For NGAUSS < 4, appropriate SWAP options are suppressed.
Only one of the LOAD AS xx options is offered - SQ when the current
function type is LN, LG when the current function type is SQ, L2 when
the current function type is LG, and LN when the current type is L2.
Selecting this option, reloads the image with the newly selection
function type and changes the menu option accordingly. The options
OFF TRANSF through TVZOOM are essentially the same as the
corresponding verbs in AIPS. CURVALUE is like the verb of that name,
but, when you press buttons A or B, the pixel under the cursor is
added to the editing list.
The SWAP n-m options invoke the interactive polygon setting operation
used by the AIPS verb TVSTAT. This starts in the "set polygon n" mode
where button A selects a vertex in the polygon, B sets the last vertex
in the polygon and gets ready to set polygon n+1, C sets the last
vertex and enters a vertex editing mode, and D sets the last vertex
and exits the polygon setting. In the vertex editing mode, move the
cursor to a vertex to be moved and press button A or B to reset its
position. After moving it to the desired point, press button A or B
to fix that point and restart the vertex editing mode. Press button C
to fix that point and then start creating polygon n+1. Press button D
to fix that point and exit the polygon setting. Once button D has
been set, the selected areas of pixels have their solutions swapped.
The images are updated and reloaded automatically.
Very large images may not be able to fit on your TV. When the image
exceeds the size of the TV, the top line will show the component
number followed by a subimage number in parentheses and the NEXT
WINDOW option will appear. The first sub-images displayed is called
number 0 and shows the full image every n'th pixel in X and Y.
Sub-image 1 begins at the lower left, moves right, then back to the
left and up, and so forth until the top right is reached. Every pixel
is displayed in these sub-images. Use the NEXT WINDOW option to step
through the sub-images in a circular fashion.