AIPS HELP file for MAXFIT in 31DEC09

As of Sat Nov 21 20:17:33 2009

INPUTS

INNAME                             Image name (name)
INCLASS                            Image name (class)
INSEQ           0.0      9999.0    Image name (seq. #)
INDISK          0.0         9.0    Disk drive #
PIXXY           0.0      4096.0    Approximate (X,Y,...) pixel
                                   of maximum
IMSIZE          3.0        16.0    Search area for peak value.
PRTLEV         -2.0        10.0    <= -1 => no display results
         @      Output adverbs
PIXXY    @                         Fitted (X,Y,...) pixel of
         @                         maximum.
PIXVAL   @                         Peak intensity at maximum
COORDINA @                         Coordinates at pixel
ERROR    @                         > 0 => fit failed, else okay

HELP SECTION

MAXFIT
Type: Verb
Use:  MAXFIT fits a quadratic function to a 3x3 map array to
      determine the position and strength of an extremum.  It
      uses PIXXY as an estimate of the center of the 3x3 array,
      but searches over an area of up to 16x16 pixels for the
      actual peak value before fitting.
Adverbs: (inputs)
  INNAME......Image name(name).       Standard defaults.
  INCLASS.....Image name(class).      Standard defaults.
  INSEQ.......Image name(seq. #).     0 => highest.
  INDISK......Disk drive # of image.  0 => any.
  PIXXY.......The approximate (X,Y,...) pixel of the maximum.
  IMSIZE......(X,Y) search area in pixels.  Verb uses 11 if
              the values are outside the range 3 to 16.
  PRTLEV......Print level: if <= -1, then do not put result info
              in message file, otherwise do the coordinate and
              flux displays.
Adverbs: (outputs)
  PIXXY.......Fitted (X,Y,...) position of peak.
  PIXVAL......Fitted intensity at the peak.
  COORDINA....The X and Y coordinates are found as:
              Xpos = abs(CO(1)) + abs(CO(2))/60 + abs(CO(3))/3600
                 if any of CO(1), CO(2), CO(3) < 0: Xpos = -Xpos
              Ypos = abs(CO(4)) + abs(CO(5))/60 + abs(CO(6))/3600
                 if any of CO(4), CO(5), CO(6) < 0: Ypos = -Ypos
              Note that, although these are most suited to RA, Dec in
              sexagesimal notation, they can be used for any type of
              coordinate.  The units are standard FITS units (e.g
              degrees, m/sec, Hz, sec, etc.) except that right
              ascensions are in hours of time.
  ERROR.......If the verb is not aborted for error, but the fit
              fails, ERROR will be TRUE (1), else it will be
              FALSE (-1).  Used to detect failures without
              stopping a procedure or RUN file.

EXPLAIN SECTION

MAXFIT: Verb to find coordinates and value of an image extremum
DOCUMENTOR: E.B.Fomalont (NRAO/VLA)
RELATED PROGRAMS:  IMFIT, MOMFT, IMVAL

                          PURPOSE

     MAXFIT is a verb which fits a quadratic function to a
specified 3x3 map area in order to determine the location and
intensity of an extremum.  An area as large as 16x16 can be
specified in IMSIZE to search for the extremum, although the
fit will only be made on the 3x3 area surrounding the extremum.
     The verb is useful for communicating the location and
intensity of the extremum to other verbs and tasks.  After
execution PIXVAL will contain the intensity and PIXXY = a,b
will contain the pixel location of the extrumum.
     MAXFIT is less sophisticated than IMFIT, which does a
linearized least-square solution on a specified map region
to a set of Gaussians.  If you want to determine the component
size, determine the errors of the parameters, or if the
component is complex in shape, the use of IMFIT is required.
     MAXFIT performs a simple least-square analysis on a 3x3
array with the function

              a + b*x + c*y + d*x*y + e*x*x + f*y*y

The location and position of the extremum is obtained from the
parameters a,b,c,d,e and f.  No error checking or goodness of
fit analysis is made in MAXFIT.
     If there is an input specification error (bad PIXVAL, bad
image name), MAXFIT aborts the input line, procedure, RUN file,
or whatever which invoked it.  However, if the fit itself is the
sole source of error, then MAXFIT does not abort the command
stream.  Instead, it sets the adverb ERROR to TRUE if the fit
fails or FALSE if it succeeds.  Procedures which depend on the
output of MAXFIT should test ERROR and do appropriate things if
it is TRUE.  For example:
        PROC FITS (I, J)
        SCALAR K
        ARRAY  VALS(20)
        PIXXY = I, J
        FOR K = 1:20;
           EGETNAME(K)
           IF ERROR THEN VALS(K) = 0;
              ELSE MAXFIT ;
              IF ERROR THEN VALS(K) = -1;
                 ELSE VALS(K) = PIXVAL;
                 END
              END
           END
        FOR K = 1:20; PRINT K,VALS(K); END
        FINISH
PRTLEV = -1 could be used to eliminate the message file displays
of all the coordinates and fluxes.  This speeds the process.