AIPS HELP file for SLFIT in 31DEC09
As of Sun Nov 22 0:09:54 2009
SLFIT: Task to fit gaussians to slice data.
INPUTS
INNAME Image name (name)
INCLASS Image name (class)
INSEQ 0.0 9999.0 Image name (seq. #)
INDISK 0.0 9.0 Disk drive #
INVERS 0.0 46655.0 Version # of SL file. 0=>last
BDROP 0.0 9999.0 Drop slice pts from beginning
EDROP 0.0 9999.0 Drop slice pts from end
NGAUSS 0.0 4.0 No of gaussian components.
LTYPE Units to use for GPOS values.
See HELP LTYPE
GMAX Initial guess of max values.
GPOS Initial guess of positions.
GWIDTH Initial guess of halfwidths.
@ Fit model parameters
FMAX @ Peak of component (JY)
@ 0-> Use maximum value
FPOS @ (X,Y) position (pixels)
@ 0-> Use position of max
FWIDTH @ (BMAJ, BMIN, PA) of comp.
@ (pixels,pixels,deg)
@ 0->Use clean beam
DOMAX $ Solve for GMAX? >0 -> yes
$ returns the error
DOPOS $ Solve for GPOS? >0 -> yes
$ returns the error
DOWIDTH $ Solve for GWIDTH? >0-> yes
$ returns the error
HELP SECTION
SLFIT
Type: Task
Use: Accept an initial guess of the parameters of up to 4 Gaussian
components of a curve and produce new values of the parameters
corresponding to a least squares fit of slice file data points.
Adverbs:
INNAME......Image name (name). Standard defaults.
INCLASS.....Image name (class). Standard defaults.
INSEQ.......Image name (seq. #). 0 => highest.
INDISK......Disk unit #. 0 => any.
INVERS......Version # of SL file. 0 => highest version #
BDROP.......No of slice pts to omit from beginning of slice.
EDROP.......No of slice points to omit from end of slice.
NGAUSS......No of gaussian components.
LTYPE.......Labeling type normally. Here it is used to
tell the program what units are used for the
GPOS, GMAX, and GWIDTH. Don't change this
after doing TKSET and/or TK1SET.
GMAX........Initial guess of maximum amplitudes.
GPOS........Initial guess of positions of the components in
GPOS(1,i). GPOS(2,i) not used.
GWIDTH......Initial guess of widths at 1/2 max amplitude in
GWIDTH(1,i). GWIDTH(2,i) and GWIDTH(3,i) are not used.
Note that the units of GMAX, GPOS, and GWIDTH are those
in the plot (e.g. mJy, arc sec or Jy, degrees or ??).
FMAX........The peak value fit for each component is returned.
FPOS........The position (X,0) fit for components is returned. The
values are in pixels in the order
(X1,0, X2,0, X3,0, X4,0).
FWIDTH......The full width at half maximum fit for components are
returned. FWIDTH(2,i) and FWIDTH(3,i) are not used.
Note that the units of FMAX, FPOS, and FWIDTH are those
in the plot (e.g. mJy, arc sec or Jy, degrees or ??).
DOMAX.......Flags for GMAX: if > 0 fit this parameter, else hold
fixed. Returned value is uncertainty in the fit
parameter.
DOPOS.......Flags for GPOS: if > 0 fit this parameter, else hold
fixed. Returned value is uncertainty in the fit
parameter.
DOWIDTH.....Flags for GWIDTH: if > 0 fit this parameter, else hold
fixed. Returned value is uncertainty in the fit
parameter.
EXPLAIN SECTION
SLFIT: Task to fit Gaussian components to a 1D slice.
DOCUMENTOR: G. A. Fickling, Eric Greisen NRAO/Charlottesville
RELATED PROGRAMS: SETSLICE, SLICE, TKSLICE, TKSET, TK1SET, TKGUESS,
TKASLICE, TVSLICE, TVASLICE, TVGUESS, TVAGUESS, TVMODEL, TVAMODEL,
TVRESID, TVARESID
PURPOSE
SLFIT fits up to four Gaussian-shaped components to a selected
part of a one dimensional slice. An initial guess must be provided
for the parameters. Because of the many different units that can be
used, the only practical way to do this is interactively using the
Tektronics screen with verb TKGUESS or the TV screen with TVGUESS as
described below. Solution and error estimates are generated and the
solution and residuals can be plotted on the Tektronics, TV. or
line-printer. An arbitrary selection of parameters may be held
constant in the solution.
The fitting algorithm is based on the subroutine LMDER in the
Argonne National Laboratory Subroutine Package. It uses a linearized
least-square solution to obtain the parameters. It assumes a baseline
at zero intensity across the slice.
Assuming that the usual GETNAME step has been done, a
typical session would go like:
INEXT 'SL'; EXTL to list the parameters of the slice files.
INVERS n to select the n th file for analysis.
TKSLICE to plot the slice on the Tektronix.
EDROP 840; BDROP 700 to select a subsection to fit.
TKSLICE to replot just the subsection.
NGAUS 2 to fit 2 Gaussians.
TKSET to set the initial guess of the
solution
The last verb will prompt you to
POSITION CURSOR AT CENTER & HEIGHT OF GAUSSIAN COMP 1
and will turn on the Tektronix crosshairs. Move the crosshairs
with the thumbwheels to the required position and press any key
EXCEPT on the Tektronix 4012 keyboard. The terminal then
requests you to
POSITION CURSOR AT HALFWIDTH OF GAUSSIAN COMPONENT 1
and turns the crosshairs back on. Move the crosshairs until
they are at the half-intensity point of the component and press
any key except . The process continues until all components
have been entered. Then type:
TKAGUESS to plot the guess on top of the slice plot.
If everything looks ok, then type:
GO SLFIT to run the task.
The TK cursor reading sometimes does not work well on X windows
screens. There are TVxxxxx verbs which do exactly the same things as
the TKxxxxx verbs.
When the task gets an answer, it will be displayed on the
AIPS monitor, recorded in the message file, and recorded in the
slice file itself. You may therefore wish to print out your
message file before running SLFIT (see PRTMSG), to separate the
SLFIT results from earlier work.
The current display of the fitted peak, position of the
peak, halfwidth, and errors is one of the parts of the program
that needs improvement. The units of the answers are not
displayed. The answers will be in the units that were displayed
on the Tektronix screen when TKSLICE was executed. You must not
change adverb LTYPE between executing TKSLICE, TKSET, and SLFIT
or the answers will be in different units from the display.
To get a hard copy of the answers:
PRTMSG to print the message file.
To display the results on the Tektronix 4012, enter:
TKSLICE to replot the slice.
TKAMODEL to add the model results to the plot.
TKARESID to add the residuals (data - model) to
the plot.
To get a higher quality plot of the results:
DORES TRUE; DOMOD TRUE to request the model and the residuals.
DOSLICE FALSE to leave the slice data out of the plot.
TASK 'SL2PL' ; GO to make a plot file.
INVERS 0 to select the latest plot file.
GO PRTPL to display it on the printer/plotter.