.help ecreidentify Jun88 noao.imred.echelle
.ih
NAME
ecreidentify -- Reidentify features in echelle spectra
.ih
USAGE
ecreidentify images reference
.ih
PARAMETERS
.ls images
Echelle images in which the features in the reference image are to be
reidentified and a new dispersion function fit.
.le
.ls reference
Echelle image with previously identified features and dispersion
function.
.le
.ls shift = 0.
Shift in user coordinates to be added to the reference features before
centering.  If INDEF then a shift is determined by correlating the
reference features to features automatically identified in the image to
be reidentified.
.le
.ls cradius = 5.
Centering radius in pixels.  If a reidentified feature falls further
than this distance from the reference position (after shifting) it is
not reidentified.
.le
.ls threshold = 10.
In order for a feature center to be determined the range of pixel
intensities around the feature must exceed this threshold.
.le
.ls refit = yes
Refit the dispersion function?  If yes and there are more than 4
features in more than one order and a dispersion function was defined
in the reference image then a new dispersion function of the same type
and order offset
as in the reference image is fit using the new pixel positions.
Otherwise only a zero point shift is determined from the revised fitted
coordinates without changing the form of the dispersion function.
.le
.ls database = "database"
Database containing the feature data for the reference image and in
which the features for the reidentified images are recorded.
.le
.ls logfiles = "STDOUT,logfile"
List of file in which to keep a processing log.  If a null file, "", is
given then no log is kept.  If the log file is "STDOUT" then the log is
written to the terminal.
.le
.ih
DESCRIPTION
Emission or absorption features in a reference echelle spectrum are
reidentified in other echelle spectra.  The features for the reference
image and those determined for reidentified images are recorded in the
specified database.

The first step in transferring identifications from the reference
spectrum to another spectrum is to add a shift (in wavelength) to each
feature in the reference image.  The shift is specified by the
parameter \fIshift\fR.  This shift is for the fundamental order (order
number 1) which is then applied to each order by dividing by the order
number.  If the shift is specified as INDEF then a shift is determined
by finding the peaks in the input spectrum and correlating these peaks
against the feature in the reference spectrum.  This is the 'x'
algorithm described in \fBecidentify\fR.

After the shift has been added to move the reference features to near
the input spectrum features these positions are adjusted by centering
on the features using the \fBcenter1d\fR algorithm.  The parameters
\fIcradius\fR and \fIthreshold\fR are used in this operation.  If the
centering fails to find the feature within the centering radius
(\fIcradius\fR) that feature is eliminated from the feature list.

If the parameter \fIrefit\fR has the value "no" then the average shift
in the feature positions is recorded as a zero point wavelength offset
for the fundamental order without changing the shape of the dispersion
function.  If the parameter has the value "yes" then the new feature
positions are used to refit the dispersion function (of the same function
type and orders).  The order offset is also maintained.

Log information is written to the specified log files.  To log this to
the terminal, called the standard output, use STDOUT.  The log
information includes reference spectrum, the spectrum being reidentified,
the number of initial features and the number actually reidentified,
the average shift in pixels, the average shift in wavelength (in terms
of the fundamental order), the average fractional shift in wavelength
(which can be scaled to a radial velocity), and the RMS of the features
wavelengths given by the dispersion function to the user specified true
wavelengths.
.ih
EXAMPLES
The features in the spectrum f033.ec were identified previously
with the task \fBecidentify\fR.  The features positions in f043.ec are
are reidentified with and without refitting the dispersion function as
follows:

.nf
ec> ecreidentify f043.ec f033.ec

ECREIDENTIFY: NOAO/IRAF V2.7 seaman@puppis Mon 09:03:51 27-Jun-88
  Reference image = f033.ec, Refit = yes
               Image    Found  Pix Shift  User Shift  Z Shift      RMS
             f043.ec  561/561       0.11       -1.07  -1.9E-6   0.0117


ec> ecreidentify f043.ec f033.ec refit=no

ECREIDENTIFY: NOAO/IRAF V2.7 seaman@puppis Mon 09:15:21 27-Jun-88
  Reference image = f033.ec, Refit = no
               Image    Found  Pix Shift  User Shift  Z Shift      RMS
             f043.ec  561/561       0.11       -1.07  -1.9E-6   0.0131
.fi
.ih
SEE ALSO
center1d, ecidentify
.endhelp
