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+.help do3fiber Feb93 noao.imred.kpnocoude
+.ih
+NAME
+do3fiber -- Three fiber data reduction task
+.ih
+USAGE
+do3fiber objects
+.ih
+SUMMARY
+The \fBdo3fiber\fR reduction task is specialized for scattered light
+subtraction, extraction, flat
+fielding, and wavelength calibration of multifiber data in which some
+fibers are used to take object spectra and other fibers are used to
+take simultaneous arc spectra.  A three fiber instrument of this
+type (one object and two arc fibers) is available at the KPNO coude feed.
+The default parameters are set for this configuration.
+If there are a large number of fibers and fiber throughput and sky
+fiber subtraction is needed the \fBdofiber\fR task should be used.
+
+The \fBdo3fiber\fR task is a command language script which collects
+and combines the functions and parameters of many general purpose tasks to
+provide a single complete data reduction path.  The task provides a degree
+of guidance, automation, and record keeping necessary when dealing with
+this type of multifiber data.
+.ih
+PARAMETERS
+.ls objects
+List of object spectra to be processed.  Previously processed spectra are
+ignored unless the \fIredo\fR flag is set or the \fIupdate\fR flag is set and
+dependent calibration data has changed.  Extracted spectra are ignored.
+.le
+.ls apref = ""
+Aperture reference spectrum.  This spectrum is used to define the basic
+extraction apertures and is typically a flat field spectrum.
+.le
+.ls flat = "" (optional)
+Flat field spectrum.  If specified the one dimensional flat field spectra
+are extracted and used to make flat field corrections.
+.le
+.ls arcs = "" (at least one if dispersion correcting)
+List of primary, all fiber arc spectra.  These spectra are used to define
+the dispersion functions for each fiber apart from a possible zero point
+correction made with simultaneous arc calibration fibers in the object
+spectra.  One fiber from the first spectrum is used to mark lines and set
+the dispersion function interactively and dispersion functions for all
+other fibers and arc spectra are derived from it.
+.le
+.ls arctable = "" (optional) (refspectra)
+Table defining arc spectra to be assigned to object
+spectra (see \fBrefspectra\fR).  If not specified an assignment based
+on a header parameter, \fIparams.sort\fR, such as the observation time is made.
+.le
+
+.ls readnoise = "RDNOISE" (apsum)
+Read out noise in photons.  This parameter defines the minimum noise
+sigma.  It is defined in terms of photons (or electrons) and scales
+to the data values through the gain parameter.  A image header keyword
+(case insensitive) may be specified to get the value from the image.
+.le
+.ls gain = "GAIN" (apsum)
+Detector gain or conversion factor between photons/electrons and
+data values.  It is specified as the number of photons per data value.
+A image header keyword (case insensitive) may be specified to get the value
+from the image.
+.le
+.ls datamax = INDEF (apsum.saturation)
+The maximum data value which is not a cosmic ray.
+When cleaning cosmic rays and/or using variance weighted extraction
+very strong cosmic rays (pixel values much larger than the data) can
+cause these operations to behave poorly.  If a value other than INDEF
+is specified then all data pixels in excess of this value will be
+excluded and the algorithms will yield improved results.
+This applies only to the object spectra and not the flat field or arc
+spectra.  For more
+on this see the discussion of the saturation parameter in the
+\fBapextract\fR package.
+.le
+.ls fibers = 3 (apfind)
+Number of fibers.  This number is used during the automatic definition of
+the apertures from the aperture reference spectrum.
+.le
+.ls width = 6. (apedit)
+Approximate base full width of the fiber profiles.  This parameter is used
+for the profile centering algorithm.
+.le
+.ls crval = INDEF, cdelt = INDEF (autoidentify)
+These parameters specify an approximate central wavelength and dispersion.
+They may be specified as numerical values, INDEF, or image header keyword
+names whose values are to be used.  If one or both of these parameters are
+specified as INDEF the search for a solution will be slower and more likely
+to fail.
+.le
+.ls objaps = "2", arcaps = "1,3"
+List of object and arc aperture numbers.  These are used to
+identify arc apertures for wavelength calibration and object apertures
+for the final results.
+.le
+
+.ls scattered = no (apscatter)
+Smooth and subtracted scattered light from the object and flat field
+images.  This operation consists of fitting independent smooth functions
+across the dispersion using data outside the fiber apertures and then
+smoothing the individual fits along the dispersion.  The initial
+flat field, or if none is given the aperture reference image, are
+done interactively to allow setting the fitting parameters.  All
+subsequent subtractions use the same fitting parameters.
+.le
+.ls fitflat = yes (flat1d)
+Fit the composite flat field spectrum by a smooth function and divide each
+flat field spectrum by this function?  This operation removes the average
+spectral signature of the flat field lamp from the sensitivity correction to
+avoid modifying the object fluxes.
+.le
+.ls recenter = yes (aprecenter)
+Recenter reference apertures for each object spectrum?
+.le
+.ls edit = no (apedit)
+Review aperture definitions for each object spectrum?  Note that this does
+not apply to the initial reference aperture which always allows
+interactive review of the aperture definitions.
+.le
+.ls clean = no (apsum)
+Detect and correct for bad pixels during extraction?  This is the same
+as the clean option in the \fBapextract\fR package.  If yes this also
+implies variance weighted extraction and requires reasonably good values
+for the readout noise and gain.  In addition the datamax parameters
+can be useful.
+.le
+.ls dispcor = yes
+Dispersion correct spectra?  Depending on the \fIparams.linearize\fR
+parameter this may either resample the spectra or insert a dispersion
+function in the image header.
+.le
+.ls splot = yes
+Plot the final spectra with the task \fBsplot\fR?
+.le
+.ls redo = no
+Redo operations previously done?  If no then previously processed spectra
+in the objects list will not be processed (unless they need to be updated).
+.le
+.ls update = yes
+Update processing of previously processed spectra if aperture, flat
+field, or dispersion reference definitions are changed?
+.le
+.ls batch = no
+Process spectra as a background or batch job provided there are no interactive
+options (\fIedit\fR and \fIsplot\fR) selected.
+.le
+.ls listonly = no
+List processing steps but don't process?
+.le
+
+.ls params = "" (pset)
+Name of parameter set containing additional processing parameters.  The
+default is parameter set \fBparams\fR.  The parameter set may be examined
+and modified in the usual ways (typically with "epar params" or ":e params"
+from the parameter editor).  Note that using a different parameter file
+is not allowed.  The parameters are described below.
+.le
+
+.ce
+-- PACKAGE PARAMETERS
+
+Package parameters are those which generally apply to all task in the
+package.  This is also true of \fBdo3fiber\fR.
+.ls observatory = "observatory"
+Observatory at which the spectra were obtained if not specified in the
+image header by the keyword OBSERVAT.  For NOAO data the image headers
+identify the observatory as "kpno" or "ctio" so this parameter is not used.
+For data from other observatories this parameter may be used
+as describe in \fBobservatory\fR.
+.le
+.ls interp = "poly5" (nearest|linear|poly3|poly5|spline3|sinc)
+Spectrum interpolation type used when spectra are resampled.  The choices are:
+
+.nf
+	nearest - nearest neighbor
+	 linear - linear
+	  poly3 - 3rd order polynomial
+	  poly5 - 5th order polynomial
+	spline3 - cubic spline
+	   sinc - sinc function
+.fi
+.le
+.ls dispaxis = 2
+Default dispersion axis.  The dispersion axis is 1 for dispersion
+running along image lines and 2 for dispersion running along image
+columns.  If the image header parameter DISPAXIS is defined it has
+precedence over this parameter.
+.le
+.ls database = "database"
+Database (directory) used for storing aperture and dispersion information.
+.le
+.ls verbose = no
+Print verbose information available with various tasks.
+.le
+.ls logfile = "logfile", plotfile = ""
+Text and plot log files.  If a filename is not specified then no log is
+kept.  The plot file contains IRAF graphics metacode which may be examined
+in various ways such as with \fBgkimosaic\fR.
+.le
+.ls records = ""
+Dummy parameter to be ignored.
+.le
+.ls version = "KPNOCOUDE: ..."
+Version of the package.
+.le
+
+.ce
+PARAMS PARAMETERS
+
+The following parameters are part of the \fBparams\fR parameter set and
+define various algorithm parameters for \fBdo3fiber\fR.
+
+.ce
+--  GENERAL PARAMETERS --
+.ls line = INDEF, nsum = 10
+The dispersion line (line or column perpendicular to the dispersion
+axis) and number of adjacent lines (half before and half after unless
+at the end of the image) used in finding, recentering, resizing,
+editing, and tracing operations.  A line of INDEF selects the middle of the
+image along the dispersion axis.
+.le
+.ls extras = no (apsum)
+Include extra information in the output spectra?  When cleaning or using
+variance weighting the cleaned and weighted spectra are recorded in the
+first 2D plane of a 3D image, the raw, simple sum spectra are recorded in
+the second plane, and the estimated sigmas are recorded in the third plane.
+.le
+
+.ce
+-- DEFAULT APERTURE LIMITS --
+.ls lower = -3., upper = 3. (apdefault)
+Default lower and upper aperture limits relative to the aperture center.
+These limits are used when the apertures are first found and may be
+resized automatically or interactively.
+.le
+
+.ce
+-- AUTOMATIC APERTURE RESIZING PARAMETERS --
+.ls ylevel = 0.05 (apresize)
+Data level at which to set aperture limits during automatic resizing.
+It is a fraction of the peak relative to a local background.
+.le
+
+.ce
+-- TRACE PARAMETERS --
+.ls t_step = 10 (aptrace)
+Step along the dispersion axis between determination of the spectrum
+positions.  Note the \fInsum\fR parameter is also used to enhance the
+signal-to-noise at each step.
+.le
+.ls t_function = "spline3", t_order = 2 (aptrace)
+Default trace fitting function and order.  The fitting function types are
+"chebyshev" polynomial, "legendre" polynomial, "spline1" linear spline, and
+"spline3" cubic spline.  The order refers to the number of
+terms in the polynomial functions or the number of spline pieces in the spline
+functions.
+.le
+.ls t_niterate = 1, t_low = 3., t_high = 3. (aptrace)
+Default number of rejection iterations and rejection sigma thresholds.
+.le
+
+.ce
+-- SCATTERED LIGHT PARAMETERS --
+.ls buffer = 1. (apscatter)
+Buffer distance from the aperture edges to be excluded in selecting the
+scattered light pixels to be used.
+.le
+.ls apscat1 = "" (apscatter)
+Fitting parameters across the dispersion.  This references an additional
+set of parameters for the ICFIT package.  The default is the "apscat1"
+parameter set.
+.le
+.ls apscat2 = "" (apscatter)
+Fitting parameters along the dispersion.  This references an additional
+set of parameters for the ICFIT package.  The default is the "apscat2"
+parameter set.
+.le
+
+.ce
+-- APERTURE EXTRACTION PARAMETERS --
+.ls weights = "none" (apsum)
+Type of extraction weighting.  Note that if the \fIclean\fR parameter is
+set then the weights used are "variance" regardless of the weights
+specified by this parameter.  The choices are:
+.ls "none"
+The pixels are summed without weights except for partial pixels at the
+ends.
+.le
+.ls "variance"
+The extraction is weighted by the variance based on the data values
+and a poisson/ccd model using the \fIgain\fR and \fIreadnoise\fR
+parameters.
+.le
+.le
+.ls pfit = "fit1d" (apsum) (fit1d|fit2d)
+Profile fitting algorithm for cleaning and variance weighted extractions.
+The default is generally appropriate for most data but users
+may try the other algorithm.  See \fBapprofiles\fR for further information.
+.le
+.ls lsigma = 3., usigma = 3. (apsum)
+Lower and upper rejection thresholds, given as a number of times the
+estimated sigma of a pixel, for cleaning.
+.le
+.ls nsubaps = 1 (apsum)
+During extraction it is possible to equally divide the apertures into
+this number of subapertures.
+.le
+
+.ce
+-- FLAT FIELD FUNCTION FITTING PARAMETERS --
+.ls f_interactive = yes (fit1d)
+Fit the composite one dimensional flat field spectrum interactively?
+This is used if \fIfitflat\fR is set and a two dimensional flat field
+spectrum is specified.
+.le
+.ls f_function = "spline3", f_order = 20 (fit1d)
+Function and order used to fit the composite one dimensional flat field
+spectrum.  The functions are "legendre", "chebyshev", "spline1", and
+"spline3".  The spline functions are linear and cubic splines with the
+order specifying the number of pieces.
+.le
+
+.ce
+-- ARC DISPERSION FUNCTION PARAMETERS --
+.ls threshold = 10. (autoidentify/identify/reidentify)
+In order for a feature center to be determined the range of pixel intensities
+around the feature must exceed this threshold.
+.le
+.ls coordlist = "linelists$idhenear.dat" (autoidentify/identify)
+Arc line list consisting of an ordered list of wavelengths.
+Some standard line lists are available in the directory "linelists$".
+.le
+.ls match = -3. (autoidentify/identify)
+The maximum difference for a match between the dispersion function prediction
+value and a wavelength in the coordinate list.
+.le
+.ls fwidth = 3.5 (autoidentify/identify)
+Approximate full base width (in pixels) of arc lines.
+.le
+.ls cradius = 4. (reidentify)
+Radius from previous position to reidentify arc line.
+.le
+.ls i_function = "legendre", i_order = 3 (autoidentify/identify)
+The default function and order to be fit to the arc wavelengths as a
+function of the pixel coordinate.  The functions choices are "chebyshev",
+"legendre", "spline1", or "spline3".
+.le
+.ls i_niterate = 3, i_low = 3.0, i_high = 3.0 (autoidentify/identify)
+Number of rejection iterations and sigma thresholds for rejecting arc
+lines from the dispersion function fits.
+.le
+.ls refit = yes (reidentify)
+Refit the dispersion function?  If yes and there is more than 1 line
+and a dispersion function was defined in the arc reference then a new
+dispersion function of the same type as in the reference image is fit
+using the new pixel positions.  Otherwise only a zero point shift is
+determined for the revised fitted coordinates without changing the
+form of the dispersion function.
+.le
+.ls addfeatures = no (reidentify)
+Add new features from a line list during each reidentification?
+This option can be used to compensate for lost features from the
+reference solution.  Care should be exercised that misidentified features
+are not introduced.
+.le
+
+.ce
+-- AUTOMATIC ARC ASSIGNMENT PARAMETERS --
+.ls select = "interp" (refspectra)
+Selection method for assigning wavelength calibration spectra.
+Note that an arc assignment table may be used to override the selection
+method and explicitly assign arc spectra to object spectra.
+The automatic selection methods are:
+.ls average
+Average two reference spectra without regard to any sort parameter.
+If only one reference spectrum is specified then it is assigned with a
+warning.  If more than two reference spectra are specified then only the
+first two are used and a warning is given.
+This option is used to assign two reference spectra, with equal weights,
+independent of any sorting parameter.
+.le
+.ls following
+Select the nearest following spectrum in the reference list based on the
+sorting parameter.  If there is no following spectrum use the nearest preceding
+spectrum.
+.le
+.ls interp
+Interpolate between the preceding and following spectra in the reference
+list based on the sorting parameter.  If there is no preceding and following
+spectrum use the nearest spectrum.  The interpolation is weighted by the
+relative distances of the sorting parameter.
+.le
+.ls match
+Match each input spectrum with the reference spectrum list in order.
+This overrides the reference aperture check.
+.le
+.ls nearest
+Select the nearest spectrum in the reference list based on the sorting
+parameter.
+.le
+.ls preceding
+Select the nearest preceding spectrum in the reference list based on the
+sorting parameter.  If there is no preceding spectrum use the nearest following
+spectrum.
+.le
+.le
+.ls sort = "jd", group = "ljd" (refspectra)
+Image header keywords to be used as the sorting parameter for selection
+based on order and to group spectra.
+A null string, "", or the word "none" may be use to disable the sorting
+or grouping parameters.
+The sorting parameter
+must be numeric but otherwise may be anything.  The grouping parameter
+may be a string or number and must simply be the same for all spectra within
+the same group (say a single night).
+Common sorting parameters are times or positions.
+In \fBdo3fiber\fR the Julian date (JD) and the local Julian day number (LJD)
+at the middle of the exposure are automatically computed from the universal
+time at the beginning of the exposure and the exposure time.  Also the
+parameter UTMIDDLE is computed.
+.le
+.ls time = no, timewrap = 17. (refspectra)
+Is the sorting parameter a 24 hour time?  If so then the time origin
+for the sorting is specified by the timewrap parameter.  This time
+should precede the first observation and follow the last observation
+in a 24 hour cycle.
+.le
+
+.ce
+-- DISPERSION  CORRECTION PARAMETERS --
+.ls linearize = yes (dispcor)
+Interpolate the spectra to a linear dispersion sampling?  If yes the
+spectra will be interpolated to a linear or log linear sampling
+If no the nonlinear dispersion function(s) from the dispersion function
+database are assigned to the input image world coordinate system
+and the spectral data are not interpolated.
+.le
+.ls log = no (dispcor)
+Use linear logarithmic wavelength coordinates?  Linear logarithmic
+wavelength coordinates have wavelength intervals which are constant
+in the logarithm of the wavelength.
+.le
+.ls flux = yes (dispcor)
+Conserve the total flux during interpolation?  If \fIno\fR the output
+spectrum is interpolated from the input spectrum at each output
+wavelength coordinate.  If \fIyes\fR the input spectrum is integrated
+over the extent of each output pixel.  This is slower than
+simple interpolation.
+.le
+.ih
+ENVIRONMENT PARAMETERS
+The environment parameter \fIimtype\fR is used to determine the extension
+of the images to be processed and created.  This allows use with any
+supported image extension.  For STF images the extension has to be exact;
+for example "d1h".
+.ih
+DESCRIPTION
+The \fBdo3fiber\fR reduction task is specialized for scattered light
+subtraction, extraction, flat
+fielding, and wavelength calibration of multifiber data in which some
+fibers are used to take object spectra and other fibers are used to
+take simultaneous arc spectra.  A three fiber instrument of this
+type (one object and two arc fibers) is available at the KPNO coude feed.
+The default parameters are set for this configuration.
+If there are a large number of fibers and fiber throughput and sky
+fiber subtraction is needed the \fBdofiber\fR task should be used.
+
+The \fBdo3fiber\fR task is a command language script which collects
+and combines the functions and parameters of many general purpose tasks to
+provide a single complete data reduction path.  The task provides a degree
+of guidance, automation, and record keeping necessary when dealing with
+this type of multifiber data.
+
+The general organization of the task is to do the interactive setup steps
+first using representative calibration data and then perform the majority
+of the reductions automatically, and possibly as a background process, with
+reference to the setup data.  In addition, the task determines which setup
+and processing operations have been completed in previous executions of the
+task and, contingent on the \fIredo\fR and \fIupdate\fR options, skip or
+repeat some or all the steps.
+
+The description is divided into a quick usage outline followed by details
+of the parameters and algorithms.  The usage outline is provided as a
+checklist and a refresher for those familiar with this task and the
+component tasks.  It presents only the default or recommended usage.  Since
+\fBdo3fiber\fR combines many separate, general purpose tasks the
+description given here refers to these tasks and leaves some of the details
+to their help documentation.
+
+\fBUsage Outline\fR
+
+.ls 6 [1]
+The images are first processed with \fBccdproc\fR for overscan,
+bias, and dark corrections.
+The \fBdo3fibers\fR task will abort if the image header keyword CCDPROC,
+which is added by \fBccdproc\fR, is missing.  If the data processed outside
+of the IRAF \fBccdred\fR package then a dummy CCDPROC keyword should be
+added to the image headers; say with \fBhedit\fR.
+.le
+.ls [2]
+Set the \fBdo3fiber\fR parameters with \fBeparam\fR.  Specify the object
+images to be processed, the flat field image as the aperture reference and
+the flat field, and one or more arc images.  If there are many
+object or arc spectra per setup you might want to prepare "@ files".
+.le
+.ls [3]
+Run the task.  This may be repeated multiple times with different
+observations and the task will generally only do the setup steps
+once and only process new images.  Queries presented during the
+execution for various interactive operations may be answered with
+"yes", "no", "YES", or "NO".  The lower case responses apply just
+to that query while the upper case responses apply to all further
+such queries during the execution and no further queries of that
+type will be made.
+.le
+.ls [4]
+The apertures are defined using the specified aperture reference image
+which is usually a flat field in which both the object and arc fibers are
+illuminated.  The specified number of fibers are found automatically and
+sequential apertures assigned.
+.le
+.ls [5]
+A query is given allowing the apertures to be interactively reviewed.
+In this mode one may adjust the aperture widths as desired either
+explicitly (:lower and :upper), with the cursor ('l' and 'u'), at a
+particular flux level ('y'), or with an automatic algorithm ('z')
+as described by \fBapresize\fR.  To exit type 'q'.
+.le
+.ls [6]
+The fiber positions at a series of points along the dispersion are measured
+and a function is fit to these positions.  This may be done interactively to
+adjust the fitting parameters.  Not all fibers need be examined and the "NO"
+response will quit the interactive fitting.  To exit the interactive
+fitting type 'q'.
+.le
+.ls [7]
+If scattered light subtraction is to be done the flat field image is
+used to define the scattered light fitting parameters interactively.
+If one is not specified then the aperture reference image is used for
+this purpose.
+
+There are two queries for the interactive fitting.  A graph of the
+data between the defined reference apertures separated by a specified
+buffer distance is first shown.  The function order and type may be
+adjusted.  After quiting with 'q' the user has the option of changing
+the buffer value and returning to the fitting, changing the image line
+or column to check if the fit parameters are satisfactory at other points,
+or to quit and accept the fit parameters.  After fitting all points
+across the dispersion another graph showing the scattered light from
+the individual fits is shown and the smoothing parameters along the
+dispersion may be adjusted.  Upon quiting with 'q' you have the option
+of checking other cuts parallel to the dispersion or quiting and finishing
+the scattered light function smoothing and subtraction.
+
+If there is a throughput image then this is corrected for scattered light
+noninteractively using the previous fitting parameters.
+.le
+.ls [8]
+If flat fielding is to be done the flat field spectra are extracted.  The
+average spectrum over all fibers is determined and a function is fit
+interactively (exit with 'q').  This function is generally of sufficiently
+high order that the overall shape is well fit.  This function is then used
+to normalize the individual flat field spectra.
+The final response spectra are normalized to a unit
+mean over all fibers.
+.le
+.ls [9]
+If dispersion correction is selected the first arc in the arc list is
+extracted.  The middle fiber is used to identify the arc lines and define
+the dispersion function using the task \fBautoidentify\fR.  The
+\fIcrval\fR and \fIcdelt\fR parameters are used in the automatic
+identification.  Whether or not the automatic identification is
+successful you will be shown the result of the arc line identification.
+If the automatic identification is not successful identify a few arc
+lines with 'm' and use the 'l' line list identification command to
+automatically add additional lines and fit the dispersion function.  Check
+the quality of the dispersion function fit with 'f'.  When satisfied exit
+with 'q'.
+.le
+.ls [10]
+The remaining fibers are automatically reidentified.  You have the option
+to review the line identifications and dispersion function for each fiber
+and interactively add or delete arc lines and change fitting parameters.
+This can be done selectively, such as when the reported RMS increases
+significantly.
+.le
+.ls [11]
+If the spectra are to be resampled to a linear dispersion system
+(which will be the same for all spectra) default dispersion parameters
+are printed and you are allowed to adjust these as desired.
+.le
+.ls [12]
+The object spectra are now automatically scattered light subtracted,
+ extracted, flat fielded, and dispersion corrected.
+The reference apertures are first assigned
+to the object spectra.  If the \fIrecenter\fR option is set the apertures
+will have a shift applied based on recentering the fiber profiles.
+If the \fIedit\fR option is set you may review and modify
+the aperture definitions interactively.  Any new
+arcs assigned to the object images are automatically extracted and
+dispersion functions determined.  A zero point wavelength correction
+is computed from the arc fiber spectra and applied to the object spectrum.
+.le
+.ls [13]
+The option to examine the final spectra with \fBsplot\fR may be given.
+To exit type 'q'.
+.le
+.ls [14]
+If scattered light is subtracted from the input data a copy of the
+original image is made by appending "noscat" to the image name.
+If the data are reprocessed with the \fIredo\fR flag the original
+image will be used again to allow modification of the scattered
+light parameters.
+
+The final spectra will have the same name as the original 2D images
+with a ".ms" extension added.
+.le
+
+\fBSpectra and Data Files\fR
+
+The basic input consists of multifiber object and calibration spectra
+stored as IRAF images.  The type of image format is defined by the
+environment parameter \fIimtype\fR.  Only images with that extension will
+be processed and created.
+There are two types of calibration images.  These
+are flat fields and comparison lamp arc spectra.  The raw CCD images must
+be processed to remove overscan, bias, and dark count effects.  This is
+generally done using the \fBccdred\fR package.
+The \fBdo3fiber\fR task will abort if the image header keyword CCDPROC,
+which is added by \fBccdproc\fR, is missing.  If the data processed outside
+of the IRAF \fBccdred\fR package then a dummy CCDPROC keyword should be
+added to the image headers; say with \fBhedit\fR.
+Flat fielding is generally
+not done at this stage but as part of \fBdo3fiber\fR.  If for some reason
+the flat field or calibration arc spectra have separate exposures through
+different fibers they may be simply added.
+
+The assignment of arc calibration exposures to object exposures is
+generally done by selecting the nearest in time and interpolating.
+However, the optional \fIarc assignment table\fR may be used to explicitly
+assign arc images to specific objects.  The format of this file is
+described in the task \fBrefspectra\fR.
+
+The final reduced spectra are recorded in one, two or three dimensional IRAF
+images.  The images have the same name as the original images with an added
+".ms" extension.  Each line in the reduced image is a one dimensional
+spectrum with associated aperture, wavelength, and identification
+information.  With a single object spectrum the image will be one dimensional
+and with multiple object spectra the image will be two dimensional.
+When the \fIextras\fR parameter is set the images will be three
+dimensional (regardless of the number of apertures) and the lines in the
+third dimension contain additional information (see
+\fBapsum\fR for further details).  These spectral formats are accepted by the
+one dimensional spectroscopy tasks such as the plotting tasks \fBsplot\fR
+and \fBspecplot\fR.
+
+\fBPackage Parameters\fR
+
+The \fBkpnocoude\fR package parameters set parameters affecting all the tasks
+in the package.  Some of the parameters are not applicable to the
+\fBdo3fiber\fR task.  The observatory parameter is only required for data
+without an OBSERVAT header parameter (currently included in NOAO data).
+The spectrum interpolation type might be changed to "sinc" but with the
+cautions given in \fBonedspec.package\fR.  The dispersion axis parameter is
+only needed if a DISPAXIS image header parameter is not defined.  The other
+parameters define the standard I/O functions.  The verbose parameter
+selects whether to print everything which goes into the log file on the
+terminal.  It is useful for monitoring what the \fBdo3fiber\fR task does.  The
+log and plot files are useful for keeping a record of the processing.  A
+log file is highly recommended.  A plot file provides a record of
+apertures, traces, and extracted spectra but can become quite large.
+The plotfile is most conveniently viewed and printed with \fBgkimosaic\fR.
+
+\fBProcessing Parameters\fR
+
+The input images are specified by image lists.  The lists may be
+a list of explicit, comma separate image names, @ files, or image
+templates using pattern matching against file names in the directory.
+The aperture reference spectrum is used to find the spectrum profiles and trace
+them.  Thus, this requires an image with good signal in all fibers
+which usually means a flat field spectrum.  It is recommended that
+flat field correction be done using one dimensional extracted spectra
+rather than as two dimensional images.  This is done if a flat field
+spectrum is specified.  The arc assignment table is used to specifically
+assign arc spectra to particular object spectra and the format
+of the file is described in \fBrefspectra\fR.
+
+The detector read out noise and gain are used for cleaning and variance
+(optimal) extraction.  The dispersion axis defines the wavelength direction
+of spectra in the image if not defined in the image header by the keyword
+DISPAXIS.  The width parameter (in pixels) is used for the profile finding and
+centering algorithm (\fBcenter1d\fR).
+
+The number of fibers is fairly obvious.  It is the number of
+fibers, including the arc fibers, to be automatically found and
+assigned apertures.  The apertures are assigned aperture
+numbers sequentially.  The object and arc fibers are identified
+by these aperture numbers as specified by the \fIobjaps\fR and
+\fIarcaps\fR parameters.  The defaults are for the case of three
+fibers in the sequence arc fiber, object fiber, and arc fiber.
+
+The approximate central wavelength and dispersion are used for the
+automatic identification of the arc reference.  They may be specified
+as image header keywords or values.  The INDEF values search the
+entire range of the coordinate reference file but the automatic
+line identification algorithm works much better and faster if
+approximate values are given.
+
+The next set of parameters select the processing steps and options.  The
+scattered light option allows fitting and subtracting a scattered light
+surface from the input object and flat field.  If there is significant
+scattered light which is not subtracted the fiber throughput correction
+will not be accurate.  The
+flat fitting option allows fitting and removing the overall shape of the
+flat field spectra while preserving the pixel-to-pixel response
+corrections.  This is useful for maintaining the approximate object count
+levels and not introducing the reciprocal of the flat field spectrum into
+the object spectra.
+
+The apertures defined for the aperture reference image are assigned to
+each image.  For the object images the apertures may be shifted across
+the dispersion by recentering the strongest profiles and averaging
+the individual shifts to form a single shift for all apertures.  This
+corrects for shifts in the detector during the observations.  The
+\fIrecenter\fR parameter selects whether to apply this shift or not.
+
+The \fIedit\fR option allows you to be queried to review the apertures
+assigned to each object image.  If selected and the query answered
+affirmatively the apertures may be interactively shifted and resized.  The
+query may also be answered with "NO" to turn off this option during
+processing.  Note that the initial aperture definitions for the aperture
+reference image always allows editing.
+
+The \fIclean\fR option invokes a profile fitting and deviant
+point rejection algorithm as well as a variance weighting of points in the
+aperture.  These options require knowing the effective (i.e. accounting for
+any image combining) read out noise and gain.  For a discussion of cleaning
+and variance weighted extraction see \fBapvariance\fR and
+\fBapprofiles\fR.
+
+The dispersion correction option selects whether to extract arc spectra,
+determine dispersion functions, assign them to the object spectra, and,
+possibly, resample the spectra to a linear (or log-linear) wavelength
+scale.
+
+The \fIsplot\fR option allows a query (which may be answered with "YES"
+or "NO" to eliminate the query) and then plotting of the final object
+spectra if answered affirmatively.  The plotting is done with the
+task \fBsplot\fR.
+
+Generally once a spectrum has been processed it will not be reprocessed if
+specified as an input spectrum.  However, changes to the underlying
+calibration data can cause such spectra to be reprocessed if the
+\fIupdate\fR flag is set.  The changes which will cause an update are a new
+reference image, new flat field, and a new arc reference image.  If all
+input spectra are to be processed regardless of previous processing the
+\fIredo\fR flag may be used.  Note that reprocessing clobbers the
+previously processed output spectra.
+
+The \fIbatch\fR processing option allows object spectra to be processed as
+a background or batch job.  This will only occur if the aperture editing
+and final spectrum plotting have been turned off, either with the task
+option parameter or by answering "NO" to the queries.  The \fIlistonly\fR
+option prints a summary of the processing steps which will be performed on
+the input spectra without actually doing anything.  This is useful for
+verifying which spectra will be affected if the input list contains
+previously processed spectra.  The listing does not include any arc spectra
+which may be extracted to dispersion calibrate an object spectrum.
+
+The last parameter (excluding the task mode parameter) points to another
+parameter set for the algorithm parameters.  The way \fBdo3fiber\fR works
+this may not have any value and the parameter set \fBparams\fR is always
+used.  The algorithm parameters are discussed further in the next section.
+
+\fBAlgorithms and Algorithm Parameters\fR
+
+This section summarizes the various algorithms used by the \fBdo3fiber\fR
+task and the parameters which control and modify the algorithms.  The
+algorithm parameters available to the user are collected in the parameter
+set \fBparams\fR.  These parameters are taken from the various general
+purpose tasks used by the \fBdo3fiber\fR processing task.  Additional
+information about these parameters and algorithms may be found in the help
+for the actual task executed.  These tasks are identified in the parameter
+section listing in parenthesis.  The aim of this parameter set organization
+is to collect all the algorithm parameters in one place separate from the
+processing parameters and include only those which are relevant for
+this type of data.  The parameter values can be changed from the
+defaults by using the parameter editor,
+.nf
+
+	cl> epar params
+
+.fi
+or simple typing \fIparams\fR.  The parameter editor can also be
+entered when editing the \fBdo3fiber\fR parameters by typing \fI:e
+params\fR or simply \fI:e\fR if positioned at the \fIparams\fR
+parameter.
+
+\fBAperture Definitions\fR
+
+The first operation is to define the extraction apertures, which include
+the aperture width and position dependence with wavelength, for the object
+and arc fibers.  This is done on a reference spectrum which is usually a
+flat field taken through both fibers.  Other spectra will inherit the
+reference apertures and may apply a correction for any shift of the orders
+across the dispersion.  The reference apertures are defined only once
+unless the \fIredo\fR option is set.
+
+The selected number of fibers are found automatically by selecting the
+highest peaks in a cut across the dispersion.  Apertures are assigned with
+a limits set by the \fIlower\fR and \fIupper\fR parameter and numbered
+sequentially.  A query is then given allowing the apertures to be reviewed
+interactively.  If answered affirmatively a cut across the orders is shown
+with the apertures marked and an interactive aperture editing mode is
+entered (see \fBapedit\fR).  The main thing to be concerned about is that
+the aperture numbers agree with the \fIobjaps\fR and \fIarcaps\fR
+definitions.  The aperture numbers may be changed with the 'i' or 'o'
+keys.  The apertures may also be resized from the default limits.
+To exit the background and aperture editing steps type 'q'.
+
+Next the positions of the fiber profiles at various points along the
+dispersion are measured and a "trace function" is fit.  The user is asked
+whether to fit the trace function interactively.  This is selected to
+adjust the fitting parameters such as function type and order.  When
+interactively fitting a query is given for each aperture.  After the first
+aperture one may skip reviewing the other traces by responding with "NO".
+Queries made by \fBdo3fiber\fR generally may be answered with either lower
+case "yes" or "no" or with upper case "YES" or "NO".  The upper case
+responses apply to all further queries and so are used to eliminate further
+queries of that kind.
+
+The above steps are all performed using tasks from the \fBapextract\fR
+package and parameters from the \fBparams\fR parameters.  As a quick
+summary, the dispersion direction of the spectra are determined from the
+package \fBdispaxis\fR parameter if not defined in the image header.  The default
+line or column for finding the orders and the number of image lines or
+columns to sum are set by the \fIline\fR and \fInsum\fR parameters.  A line
+of INDEF (the default) selects the middle of the image.  The automatic
+finding algorithm is described for the task \fBapfind\fR and basically
+finds the strongest peaks.  The tracing is done as described in
+\fBaptrace\fR and consists of stepping along the image using the specified
+\fIt_step\fR parameter.  The function fitting uses the \fBicfit\fR commands
+with the other parameters from the tracing section.
+
+\fBExtraction\fR
+
+The actual extraction of the spectra is done by summing across the fixed
+width apertures at each point along the dispersion.  The default is to
+simply sum the pixels using partial pixels at the ends.  There is an
+option to weight the sum based on a Poisson noise model using the
+\fIreadnoise\fR and \fIgain\fR detector parameters.  Note that if the
+\fIclean\fR option is selected the variance weighted extraction is used
+regardless of the \fIweights\fR parameter.  The sigma thresholds for
+cleaning are also set in the \fBparams\fR parameters.
+
+The cleaning and variance weighting options require knowing the effective
+(i.e. accounting for any image combining) read out noise and gain.  These
+numbers need to be adjusted if the image has been processed such that the
+intensity scale has a different origin (such as a background light
+subtraction) or scaling (such as caused by unnormalized flat fielding).
+For optimal extraction and cleaning to work it is recommended that
+a \fIdatamax\fR value be determined for the data and the
+\fIfitflat\fR option be used.  For further discussion of cleaning and
+variance weighted extraction see \fBapvariance\fR and \fBapprofiles\fR as
+well as  \fBapsum\fR.
+
+\fBScattered Light Subtraction\fR
+
+Scattered light may be subtracted from the input two dimensional image as
+the first step.  This is done using the algorithm described in
+\fBapscatter\fR.  This can be important if there is significant scattered
+light since the flat field/throughput correction will otherwise be
+incorrect.  The algorithm consists of fitting a function to the data
+outside the defined apertures by a specified \fIbuffer\fR at each line or
+column across the dispersion.  The function fitting parameters are the same
+at each line.  Because the fitted functions are independent at each line or
+column a second set of one dimensional functions are fit parallel to the
+dispersion using the evaluated fit values from the cross-dispersion step.
+This produces a smooth scattered light surface which is finally subtracted
+from the input image.  Again the function fitting parameters are the
+same at each line or column though they may be different than the parameters
+used to fit across the dispersion.
+
+The first time the task is run with a particular flat field (or aperture
+reference image if no flat field is used) the scattered light fitting
+parameters are set interactively using that image.  The interactive step
+selects a particular line or column upon which the fitting is done
+interactively with the \fBicfit\fR commands.  A query is first issued
+which allows skipping this interactive stage.  Note that the interactive
+fitting is only for defining the fitting functions and orders.  When
+the graphical \fBicfit\fR fitting is exited (with 'q') there is a second prompt
+allowing you to change the buffer distance (in the first cross-dispersion
+stage) from the apertures, change the line/column, or finally quit.
+
+The initial fitting parameters and the final set parameters are recorded
+in the \fBapscat1\fR and \fBapscat2\fR hidden parameter sets.  These
+parameters are then used automatically for every subsequent image
+which is scattered light corrected.
+
+The scattered light subtraction modifies the input 2D images.  To preserve
+the original data a copy of the original image is made with the same
+root name and the word "noscat" appended.  The scattered light subtracted
+images will have the header keyword "APSCATTE" which is how the task
+avoids repeating the scattered light subtraction during any reprocessing.
+However if the \fIredo\fR option is selected the scattered light subtraction
+will also be redone by first restoring the "noscat" images to the original
+input names.
+
+\fBFlat Field Correction\fR
+
+Flat field corrections may be made during the basic CCD processing; i.e.
+direct division by the two dimensional flat field observation.  In that
+case do not specify a flat field spectrum; use the null string "".  The
+\fBdo3fiber\fR task provides an alternative flat field response correction
+based on division of the extracted object spectra by the extracted flat field
+spectra.  A discussion of the theory and merits of flat fielding directly
+verses using the extracted spectra will not be made here.  The
+\fBdo3fiber\fR flat fielding algorithm is the \fIrecommended\fR method for
+flat fielding since it works well and is not subject to the many problems
+involved in two dimensional flat fielding.
+
+The first step is extraction of the flat field spectrum, if specified,
+using the reference apertures.  Only one flat field is allowed so if
+multiple flat fields are required the data must be reduced in groups.
+If the \fIfitflat\fR
+option is selected (the default) the extracted flat field spectra are
+averaged together and a smooth function is fit.  The default fitting
+function and order are given by the parameters \fIf_function\fR and
+\fIf_order\fR.  If the parameter \fIf_interactive\fR is "yes" then the
+fitting is done interactively using the \fBfit1d\fR task which uses the
+\fBicfit\fR interactive fitting commands.
+
+The fitted function is divided into the individual flat field spectra to
+remove the basic shape of the spectrum while maintaining the relative
+individual pixel responses and any fiber to fiber differences.  This step
+avoids introducing the flat field spectrum shape into the object spectra
+and closely preserves the object counts.
+
+The final step is to normalize the flat field spectra by the mean counts over
+all the fibers.  This normalization step is simply to preserve the average
+counts of the extracted object and arc spectra after division by the
+response spectra.
+
+\fBDispersion Correction\fR
+
+If dispersion correction is not selected, \fIdispcor\fR=no, then the object
+spectra are simply extracted.  If it is selected the arc spectra are used
+to dispersion calibrate the object spectra.  There are four steps involved;
+determining the dispersion functions relating pixel position to wavelength,
+assigning the appropriate dispersion functions to a particular observation,
+determining a zero point wavelength shift from the arc fibers to be applied
+to the object fiber dispersion functions, and either storing the nonlinear
+dispersion function in the image headers or resampling the spectra to
+evenly spaced pixels in wavelength.
+
+The first arc spectrum in the arc list is used to define the reference
+dispersion solution.  It is extracted using the reference aperture
+definitions.  The interactive task \fBautoidentify\fR is used to
+automatically define the dispersion function in one fiber.  Whether or not
+it is successful the user is presented with the interactive identification
+graph.  The automatic identifications can be reviewed and a new solution or
+corrections to the automatic solution may be performed.  The dispersion
+functions for the other fibers are then determined automatically by
+reference to the first fiber using the task \fBreidentify\fR.  Except in
+batch mode a query is given allowing the reidentified arc spectra to be
+examined interactively with \fBidentify\fR.  This would normally be done
+only if the information about the reidentification printed on the terminal
+indicates a problem such as a large increase in the RMS.  This query may be
+eliminated in the usual way.
+
+The set of arc dispersion function parameters are from \fBautoidentify\fR and
+\fBreidentify\fR.  The parameters define a line list for use in
+automatically assigning wavelengths to arc lines, a parameter controlling
+the width of the centering window (which should match the base line
+widths), the dispersion function type and order, parameters to exclude bad
+lines from function fits, and parameters defining whether to refit the
+dispersion function, as opposed to simply determining a zero point shift,
+and the addition of new lines from the line list when reidentifying
+additional arc spectra.  The defaults should generally be adequate and the
+dispersion function fitting parameters may be altered interactively.  One
+should consult the help for the two tasks for additional details of these
+parameters and the operation of \fBautoidentify\fR.
+
+If resampling of the spectra is selected by the parameter \fIlinearize\fR
+all the arc dispersion functions are combined to provide a default
+starting and ending wavelength and dispersion with the same number of
+pixels is determined and the user is queried for any changes.  This
+linear dispersion system will be applied to all spectra so that all
+the final processed object spectra will have the same dispersion
+sampling.
+
+Once the reference dispersion functions are defined other arc spectra are
+extracted as they are assign to the object spectra.  The assignment of
+arcs is done either explicitly with an arc assignment table (parameter
+\fIarctable\fR) or based on a header parameter such as a time.
+The assignments are made by the task \fBrefspectra\fR.  When two arcs are
+assigned to an object spectrum an interpolation is done between the two
+dispersion functions.  This makes an approximate correction for steady
+drifts in the dispersion.  Because the arc fibers monitor any zero point
+shifts in the dispersion functions, due to translation and rotation of the
+detector, it is probably only necessary to have one or two arc spectra, one
+at the beginning and/or one at the end of the night.
+
+The tasks \fBsetjd\fR and \fBsetairmass\fR are automatically run on all
+spectra.  This computes and adds the header parameters for the Julian date
+(JD), the local Julian day number (LJD), the universal time (UTMIDDLE), and
+the air mass at the middle of the exposure.  The default arc assignment is
+to use the Julian date grouped by the local Julian day number.  The
+grouping allows multiple nights of data to be correctly assigned at the
+same time.
+
+When the object spectra are extracted so are the simultaneous arc spectra.
+A zero point shift of the arc spectra relative to the dispersion solutions
+of an assigned full arc observation is computed using \fBreidentify\fR.
+The zero point shifts from the arc fibers are then
+interpolated across the detector based on the positions of the arc
+apertures to the positions of the object apertures.  A linear interpolation
+is used which accounts for a rotation of the detector as well as a
+translation along the dispersion.  The interpolated zero point wavelength
+shifts are then added to the dispersion functions from the full arc
+observation for the object fibers.  Note that this does not assume that the
+object and arc fiber dispersion functions are the same or have the same
+wavelength origin, but only that the interpolated shifts in wavelength zero
+point apply to all fibers.  When there are two assigned full arc spectra
+the above steps are done independently and the final pair of zero point
+corrected dispersion functions for each object fiber are combined using the
+assigned weights.  Once the dispersion function correction is determined
+from the extracted arc fiber spectra they are deleted leaving only the
+object spectra.
+
+The last step of dispersion correction is setting the dispersion
+of the object spectra.  There are two choices here.
+If the \fIlinearize\fR parameter is not set the nonlinear dispersion
+functions are stored in the image header.  Other IRAF tasks interpret
+this information when dispersion coordinates are needed for plotting
+or analysis.  This has the advantage of not requiring the spectra
+to be interpolated and the disadvantage that the dispersion
+information is only understood by IRAF tasks and cannot be readily
+exported to other analysis software.
+
+If the \fIlinearize\fR parameter is set then the spectra are resampled to a
+linear dispersion relation either in wavelength or the log of the
+wavelength.  The linear dispersion parameters are those defined
+previously for the arc reference image.
+
+The linearization algorithm  parameters allow selecting the interpolation
+function type, whether to conserve flux per pixel by integrating across the
+extent of the final pixel, and whether to linearize to equal linear or
+logarithmic intervals.  The latter may be appropriate for radial velocity
+studies.  The default is to use a fifth order polynomial for interpolation,
+to conserve flux, and to not use logarithmic wavelength bins.  These
+parameters are described fully in the help for the task \fBdispcor\fR which
+performs the correction.
+.ih
+EXAMPLES
+1.  The following example uses artificial data and may be executed
+at the terminal (with IRAF V2.10).  This is also the sequence performed
+by the test procedure "demos do3fiber".
+
+.nf
+kp> demos mkdo3fiber
+Creating image demoobj ...
+Creating image demoflat ...
+Creating image demoarc ...
+kp> do3fiber demoobj apref=demoflat flat=demoflat arcs=demoarc \
+>>> width=4 edit=yes
+Set reference apertures for demoflat
+Resize apertures for demoflat?  (yes):
+Edit apertures for demoflat?  (yes):
+<Exit with 'q'>
+Fit traced positions for demoflat interactively?  (yes):
+Fit curve to aperture 1 of demoflat interactively  (yes):
+<Exit with 'q'>
+Fit curve to aperture 2 of demoflat interactively  (yes): N
+Create response function demoflatnorm.ms
+Extract flat field demoflat
+Fit and ratio flat field demoflat
+Create the normalized response demoflatnorm.ms
+demoflatnorm.ms -> demoflatnorm.ms  using bzero: 0.  and bscale: 1.
+    mean: 1.  median: 1.034214  mode: 0.8378798
+    upper: INDEF  lower: INDEF
+Average aperture response:
+1.  0.8394014
+2.  1.034403
+3.  1.126194
+Extract arc reference image demoarc
+Determine dispersion solution for demoarc
+<Reset default line list with ":coord linelists$idhenear.dat">
+<A dispersion solution is found automatically.>
+<Examine the fit with 'f'>
+<Exit fit with 'q' and exit task with 'q'>
+
+REIDENTIFY: NOAO/IRAF V2.10BETA valdes@puppis Fri 11:04:32 06-Mar-92
+  Reference image = demoarc.ms, New image = demoarc.ms, Refit = yes
+     Image Data Found    Fit Pix Shift  User Shift  Z Shift     RMS
+d...ms - Ap 1   30/30  29/30  -0.00675       -0.04  -6.9E-6   0.252
+Fit dispersion function interactively? (no|yes|NO|YES) (yes): n
+d...ms - Ap 3   30/30  29/30   -0.0154     -0.0928  -1.4E-5   0.303
+Fit dispersion function interactively? (no|yes|NO|YES) (no): y
+<Exit with 'q'>
+d...ms - Ap 3   30/30  29/30   -0.0154     -0.0928  -1.4E-5   0.303
+
+Dispersion correct demoarc
+d...ms: w1 = 5785.86, w2 = 7351.59, dw = 6.14, nw = 256
+  Change wavelength coordinate assignments? (yes|no|NO): N
+Extract object spectrum demoobj
+Edit apertures for demoobj?  (yes): n
+Assign arc spectra for demoobj
+[demoobj] refspec1='demoarc'
+Reidentify arc fibers in demoobj with respect to demoarc
+
+REIDENTIFY: NOAO/IRAF V2.10BETA valdes@puppis Fri 11:04:52 06-Mar-92
+  Reference image = demoarc.ms, New image = demoobjarc.ms, Refit = no
+  Image Data   Found    Fit Pix Shift  User Shift  Z Shift     RMS
+d...ms - Ap 1  27/30  27/27   0.00502      0.0263  3.99E-6   0.175
+d...ms - Ap 3  27/30  27/27   8.62E-4       0.006  5.07E-7   0.248
+Dispersion correct demoobj
+demoobj.ms.imh: REFSHFT1 = 'demoobjarc.ms interp', shift = -0.0050,
+rms = 0.00282813 intercept = -0.0118401, slope = 2.70764E-4
+d...ms: ap = 2, w1 = 5785.86, w2 = 7351.59, dw = 6.14, nw = 256
+demoobj.ms.imh:
+Splot spectrum? (no|yes|NO|YES) (yes):
+<Exit with 'q'>
+.fi
+.ih
+REVISIONS
+.ls DO3FIBER V2.11
+The initial arc line identifications is done with the automatic line
+identification algorithm.
+.le
+.ls DO3FIBER V2.10.3
+The usual output WCS format is "equispec".  The image format type to be
+processed is selected with the \fIimtype\fR environment parameter.  The
+dispersion axis parameter is now a package parameter.  Images will only
+be processed if the have the CCDPROC keyword.  A \fIdatamax\fR parameter
+has been added to help improve cosmic ray rejection.  A scattered
+light subtraction processing option has been added.
+.le
+.ih
+SEE ALSO
+apedit, apfind, approfiles, aprecenter, apresize, apsum, aptrace, apvariance,
+ccdred, center1d, dispcor, fit1d, icfit, identify, observatory,
+onedspec.package, refspectra, reidentify, setairmass, setjd
+.endhelp