CENTERS-Generate file of object centroids from ICUR, IGCUR or IMPOS output

Description:

Figaro function that takes a list of approximate X,Y positions of objects in a two-dimensional direct image and calculates centroids (that is, accurate positions) for these objects.

The approximate positions input are obtained from environment variables. These variables should be set up prior to running CENTERS, usually by using Figaro functions IGCUR or ICUR. Alternatively, you may enter the positions into a text file and use IMPOS to read this file and copy the values into the environment variables required by CENTERS.

The computed centroids are output to a new file called center.dat.

Parameters:

IMAGE

The name of the image containing the objects. This need not be the image used to generate the original list of points - it may be a similar image in a different waveband, with offsets in X and Y with respect to the original image.

APERTURE

The aperture used for the centroiding. The aperture actually used is a box APERTURE*2+1 pixels square, which is a rough approximation to a circle of radius APERTURE.

XOFF

The offset in X, in pixels.

YOFF

The offset in Y, in pixels.

PROFBOX

Size of profile box.

PROFMIN

Minimum displayed value.

PROFMAX

Maximum displayed value.

PFILE

If set, a formatted file giving the summed radial profiles will be produced.

DISPROF

If set, the profile is displayed.

CHGPROF

If set, the profile display can be changed.

Source comments:

 C E N T E R S

 Figaro function that takes a list of approximate X,Y positions
 of objects in a two-dimensional direct image and calculates
 centroids (that is, accurate positions) for these objects.

 The approximate positions input are obtained from environment
 variables.  These variables should be set up prior to running
 CENTERS, usually by using Figaro functions IGCUR or ICUR.
 Alternatively, you may enter the positions into a text file and use
 IMPOS to read this file and copy the values into the environment
 variables required by CENTERS.

 The computed centroids are output to a new file called center.dat.

 Command parameters -

 IMAGE    (Character) The name of the image containing the
          objects.  This need not be the image used to
          generate the original list of points - it may be
          a similar image in a different waveband, with 
          offsets in X and Y with respect to the original image.
 APERTURE (Integer) The aperture used for the centroiding.
          The aperture actually used is a box APERTURE*2+1
          pixels square, which is a rough approximation to a
          circle of radius APERTURE.
 XOFF     (Real) The offset in X, in pixels.
 YOFF     (Real) The offset in Y, in pixels.
 PROFBOX  (Real) Size of profile box.
 PROFMIN  (Real) Minimum displayed value.
 PROFMAX  (Real) Maximum displayed value.

 Command keywords -

 PFILE    If specified, a formatted file giving the summed
          radial profiles will be produced.
 DISPROF  If specified, the profile is displayed.
 CHGPROF  If specified, the profile display can be changed.

 User variables - (">" input

 (>) SOFT    (Character) The current device/type for soft plots.
 (>) NPIXELS (Real) Number of objects for which positions are
              specified.
 (>) XPIXELS (Real array) List of approximate X positions of the
             objects for which the centroids are to be computed
             (pixels).
 (>) YPIXELS (Real array) List of approximate Y positions of the
             objects for which the centroids are to be computed
             (pixels).

 Output -

 center.dat contains one record for each point, giving
            XCENT,YCENT,IX,IY,DX,DY,AP 
            in the format 2F8.2,2I5,2F8.2,I4 where
            XCENT,YCENT give the position of the centroid
            IX,IY are the original pixel position of the point.
            DX,DY are the offsets in X and Y, and
            AP is the value used for APERTURE.
            If the centroid for a point cannot be determined, a
            record is written giving 
            '*** No centroid ',IX,IY,DX,DY,AP
            in the format A,2I5,2F8.2,I4.
                
                                     KS / CIT 29th Sept 1983