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+.help specfocus Nov01 noao.obsutil
+.ih
+NAME
+specfocus -- Determine spectral focus and alignment variations
+.ih
+USAGE
+specfocus images
+.ih
+PARAMETERS
+.ls images
+List of 1D or 2D focus images.  Typically the input is a list of raw
+2D CCD images of arc slit spectra.  The 1D image input is provided to
+allow use of extraction techniques beyond those provided by this task.
+.le
+.ls focus = ""
+List of focus identification values to be associated with each input image
+or an image header keyword containing the values.  The list may be an
+explicit list of values, a range specification, an @ file containing the
+values, or an image header keyword.  If none of these is given the
+identification values are simple index values in the order of the input
+images.  A range specification has the forms A, AxC, A-BxC where A is a
+starting value, B is an ending value, and C is an increment.
+.le
+.ls corwidth = 20.
+Correlation width in pixels.
+.le
+.ls level = 0.5
+Percent or fraction of the correlation peak at which to measure focus
+widths.  The default is 50% or full width at half maximum.
+.le
+.ls shifts = yes
+Compute dispersion shifts across the dispersion when there are multiple
+samples?  If yes and there are multiple samples across the dispersion
+(\fIndisp\fR > 1), pixel shifts relative to the central sample are
+determine by crosscorrelation.
+.le
+
+.ls dispaxis = 2
+Dispersion axis for 2D images.  The image header keyword DISPAXIS has
+precedence over this value.
+.le
+.ls nspectra = 1, ndisp = 1
+The number of spectral samples across the dispersion
+and the number of subpieces along the dispersion to divide the spectra
+into.  If \fInspectra\fR is greater than one then information about
+variations across the dispersion will be determined and if \fIndisp\fR is
+greater than 1 information about variations along the dispersion will be
+determined.  \fINspectra\fR applies only to 2D images.  For 1D spectra in
+multispec format each line is used as a separate sample.
+.le
+.ls slit1 = INDEF, slit2 = INDEF
+The lower and upper edges of the slit (or data region) in pixel
+coordinates (lines or columns) across the dispersion axis.  A value
+of INDEF specifies the image edges.
+.le
+
+.ls logfile = "logfile"
+File in which to record the results.  If no file is specified no log
+output is produced.
+.le
+.ih
+CURSOR COMMANDS
+All keys select an image and a sample (one of the \fIndisp\fR samples along
+the dispersion and one of the \fInspectra\fR samples across the dispersion)
+which is then generally highlighted.
+
+.nf
+   ?  Help summary
+   b  Best focus at each sample summary graphs
+   d  Delete image, sample, or point
+   p  Profiles at one sample for all images and all samples for one image
+   q  Quit
+   r  Redraw
+   s  Spectra at one sample for all images and all samples for one image
+   u  Undelete spectrum, sample, or point
+   w  Profile widths verses focus and distribution of widths
+   z  Zoom on a single sample showing correlation profile and spectrum
+   <space>  Status line output for selected image and sample
+.fi
+
+.ih
+DESCRIPTION
+This task estimates the dispersion width of spectral lines in sequences of
+arc spectra taken at different focus settings (or with some other parameter
+varied).  The widths can be measured at different spatial and dispersion
+positions, called "samples", on the detector.  The width estimates are
+recorded and displayed graphically to investigate dependencies and
+determine appropriate settings for the spectrograph setup.  The task may
+also measure dispersion shifts when multiple spectral samples are
+specified.  This task does not measure the focus point-spread-function
+width across the dispersion.
+
+The input images are specified with an image template list.  The list may
+consist of explicit image names, wildcard templates, and @ files.  A
+"focus" value is associated with each image.  This may be any numeric
+quantity (integer or floating point).  The focus values may be specified in
+several ways.  If no value is given then index numbers are assigned to
+the images in the order in which they appear in the image list.  A range
+list may be specified as described in the help topic \fBranges\fR.  This
+consists of individual values, ranges of values, a starting value and a
+step, and a range with a step.  The elements of the list are separated by
+commas, ranges are separated by hyphens, and a step is indicated by the
+character 'x'.  Long range lists, such as a list of individual focus
+values, may be placed in a file and specified with the @<filename>
+convention.  Finally, a parameter in the image header may be used for the
+focus values by simply specifying the parameter name.
+
+Two dimensional long slit images are summed into one or more one
+dimensional spectra across the dispersion.  The dispersion axis is defined
+either by the image header parameter DISPAXIS or the \fIdispaxis\fR task
+parameter with the image header parameter having precedence.  The range of
+lines or columns across the dispersion to be used is specified by the
+parameters \fIslit1\fR and \fIslit2\fR.  If specified as INDEF then the
+image limits are used.  This range is then divided into the number of
+spectra given by the parameter \fInspectra\fR.  Use of more than one
+spectrum across the dispersion allows investigation of variations along the
+slit.  In addition, if the parameter \fIshifts\fR is set the spectrum
+nearest the center is used as a reference against which shifts in the
+dispersion positions of the features in the other spectra are determined by
+crosscorrelation.
+
+The conversion of two dimensional spectra to one dimensional spectra may
+also be performed separately using the tasks in the \fBapextract\fR
+package.  This would be done typically for multifiber or echelle format
+spectra.  If the two dimensional spectra have been extracted to one
+dimensional spectra in this way the task ignores the dispersion axis and
+number of spectra parameters.  The data limits (\fIslit1\fR and
+\fIslit2\fR) are still used to select a range of lines in  "multispec"
+format images.  The \fIshifts\fR parameter also applies when there are
+multiple spectra per image.  However, it does not make sense in the case of
+echelle spectra and so it should be set to no in that case.
+
+In addition to dividing the spatial axis into a number of spectra the
+dispersion axis may also be divided into a set of subspectra.  The number
+of divisions is specified by the \fIndisp\fR parameter which applies to
+both long slit and 1D extracted spectra.  When the dispersion axis is
+divided into more than one sample, the dependence of the dispersion widths
+and shifts along the dispersion may be investigated.
+
+Each spectral sample has a low order continuum subtracted using a
+noninteractive iterative rejection algorithm to exclude the spectral
+lines.  This technique is described further under the topic
+\fIcontinuum\fR.  The continuum subtracted spectrum is then tapered with a
+cosine bell function and autocorrelated.  The length of the taper and the
+range of shifts for the correlation is set by the \fIcorwidth\fR
+parameter.  This parameter should be only slightly bigger than the expected
+feature widths to prevent correlations between different spectral lines.
+The correlation profile is offset to zero at the edges of the profile and
+normalized to unity at the profile center.  The profiles may be viewed as
+described below.
+
+If there is more than one spatial sample the central spectrum is also
+crosscorrelated against the other spectra at the same dispersion
+sample.  The crosscorrelation is computed in exactly the same way as
+the autocorrelation.  The crosscorrelation profiles are only used for
+determining shifts between the two samples and are not used in the
+width determinations.
+
+A cubic spline interpolator is fit to the profiles and this interpolation
+function is used to determined the profile width and center.  The width is
+measured at a point given by the \fIlevel\fR parameter relative to the
+profile peak.  It may be specified as a fraction of the peak if it is less
+than one or a percentage of the peak if it is greater than one.  The
+default value of 0.5 selects the full width at half maximum.  The
+autocorrelation width is divided by the square root of two to yield an
+estimate of the width of the spectral features in the spectrum in units of
+pixels.
+
+Having computed the width and shift for each input image at each sample,
+the "best focus" values (focus, width, and shift) are estimated for each
+sample.  As discussed later, it is possible to exclude some samples
+from this calculation by deleting them graphically.
+First the images with the smallest measured width at each distinct
+focus are selected since it is possible to input more than one image at the
+same focus.  The selected images are sorted by focus value and the image
+with the smallest width is found.  If that image has the lowest or highest
+focus (which will always be the case if there are only one or two images)
+then the best focus, width, and shift are those measured for that image.
+If there are three or more focus values and the minimum width focus image
+is not an endpoint then parabolic interpolation is used to find the minimum
+width.  The focus at this minimum width is the "best focus".
+The dispersion shift is the parabolic interpolation of the shifts at
+the best focus.  The "average best focus" values are then the average of
+the "best focus" values over all samples.
+
+After computing the correlation profiles, the profile widths and shifts,
+and the best focus values, an interactive graphics mode is entered.  This
+is described in detail below.  The graphics mode is exited with the 'q'
+key.  At this point the results are written to the standard output (usually
+the terminal) and to a logfile if one is specified.  The output begins with
+a banner identifying the task, version of IRAF, the user, and the date and
+time.  The next line gives the best average focus and width.  This banner
+also appears in all plots.  Then each image is listed with the focus value
+and average width (over all samples).  Finally the image with the smallest
+average width is identified and tables showing the width and shifts (if
+computed) at each sample position are printed.  If there is only one sample
+then the tables are not output.
+
+INTERACTIVE GRAPHICS MODE
+
+There are five types of plot formats which are selected with the 'b', 'p',
+'s', 'w', and 'z' keys.  The available formats and their content are
+modified depending on the number of images and the number of samples.  If
+there is only one image or one sample per image some of the plot formats
+are not available.  If there are a large number of images or a large number
+of samples the content of the plot formats may be abbreviated for
+legibility.
+
+In all plots there is a concept of the current image and the current
+sample.  In general there is an indication, usually a box, of which image
+and sample is the current one.  The current image and sample are
+changed by pointing at a particular point, box, circle, or symbol for that
+image and sample and typing a key.
+
+The 'b' key produces summary graphs of the best focus values (as described
+above) at each sample position.  There must be more than one image and more
+than one sample (either along or across the dispersion or both).  This is
+the initial plot shown when this condition is satisfied.  The central graph,
+which is always drawn, represents the best focus (smallest) width at each
+sample by circles of size proportional to the width.  The position of the
+circle indicates the central line and column of the sample.  If there are
+multiple samples across the dispersion and the \fIshifts\fR parameter is
+set then little vectors are also drawn from the center of the circle in the
+direction of the shift and with length proportional to the shift.  If there
+are 5 or fewer samples in each dimension the values of the best focus and
+the width and shift (if computed and nonzero) at that focus, are printed on
+the graph next to the circles.  If there are more samples this information
+may be obtained by pointing at the sample and typing the space key.
+
+In addition to the spatial graph there may be graphs along the line or column
+axes.  These graphs again show the widths as circles but one axis is either
+the line or column and the other axis is either the best focus value or the
+shift.  The focus graph marks the best average focus (over all samples) by
+a dashed line and a solid line connects the mean focus at each column or
+line.  The focus graphs will only appear if there is more than one sample
+along a particular image axis.  The shift graphs will only appear if the
+shifts are computed (\fIshifts\fR parameter is yes) and there is more than
+one sample along a particular dimension.  Lines are drawn at zero shift and
+connecting the mean shift at each point along the spatial axis.  Note that
+there is always a point at zero shift which is the reference sample.
+
+The best focus graphs are the exception in showing a current image and
+sample.  When changing to one of the other plots based on a current image
+and sample the circle from the central spatial graph nearest the cursor is
+used (note that the other focus and shift graphs are ignored).  The sample
+is defined by it's spatial position and the image is the one with
+focus closest to the best focus value of that sample.
+
+The 'w' key produces a graph showing the sample widths as a function of
+focus value.  There must be more than one image and more than one sample
+for this type of graph.  The top graph is a symbol plot of width verses
+focus.  The symbols are crosses except for the current image which is shown
+with pluses.  The current sample is highlighted with a box.  Also shown is
+a long dashed line connecting the widths for the current sample at each
+focus value and short dashed lines showing the best average focus and
+width.
+
+The lower portion of the 'w' key are graphs showing the
+widths as circles with size proportional to the width and position
+corresponding to the spatial position of the sample in the image.  If there
+are more than 5 samples in either dimension the graph is for the current
+image.  Otherwise there is a box for each image with the focus value
+(provided there are not too many images) indicated.  The circles are
+arranged as they would be spatially in columns and rows.  The samples
+closest to the best focus are indicated by pluses.  This allows seeing
+where the best focus values cluster.  The current image and sample are
+indicated by highlighting boxes.
+
+The 'p' key produces graphs of the autocorrelation profiles.  This also
+requires more than one image and more than one sample.  The top graph shows
+the profiles of all images at a particular sample and the bottom graph shows
+the profiles of all samples at a particular image.  The bottom sample boxes
+are arranged in columns and rows in the same way the samples are
+distributed in the image.  The current image and current sample are
+highlighted by a box.
+
+The profiles are drawn with a solid line using the interpolator function
+and the actual pixel lags are indicated with pluses.  The profiles are
+drawn shifted by the amount computed from the crosscorrelation.
+Note that the shift is added to the autocorrelation profile
+and the crosscorrelation profile is not what is plotted.  The zero shift
+position is indicated by a vertical line.  If there are less than 25 boxes
+the boxes are labeled by the width, shift (if nonzero), and focus.
+
+The 's' key plot is similar to the 'p' key plot but shows the spectra
+rather than the profiles.  The top graphs are the spectra of each image at
+a particular sample and the bottom graphs are the spectra of each sample
+for a particular image.  The current image and sample are highlighted by a
+box.
+
+The 'z' key graphs the autocorrelation profile and the spectrum
+of a single sample.  This graph provides scales which are not
+provided with the 'p' and 's' graphs.  If there is only one image
+and one sample then this is the only plot available.
+
+It is possible to exclude some of the samples from the calculation
+of the best focus and best average focus values.  This is done by
+deleting them using the 'd' key.  When using the 'd' key you must
+specify the sample to be deleted in one of the graphs.  You are
+then asked if only that sample (point) is to be deleted, if all
+samples from that image are to be deleted, or if the same sample
+from all images is to be deleted.  The deleted data is no longer
+shown explicitly but the space occupied by the data is still present
+so that the data may be included again by typing the 'u' undelete
+key.  When the task is exited with the 'q' key the printed and
+logged results will have the deleted data excluded.
+
+The remaining cursor keys do the following.  The '?' key gives a
+summary of the cursor keys.  The 'r' key redraws the current plot.
+The space key prints information about the current sample.  This
+is mostly used when there are too many images or samples to annotate
+the graphs with the focus, width, and shift.  Finally the 'q'
+key quits the task.
+.ih
+EXAMPLES
+1.  A series of 2D focus images is obtained with focus values
+starting at 400 in steps of -50.  The slit is between columns 50
+and 130.  There are 3 samples across the dispersion and 3 along
+the dispersion.
+
+.nf
+    cl> lpar specfocus
+	   images = "@imlist"       List of images
+	   (focus = "400x-50")     Focus values
+	(corwidth = 20)             Correlation width
+	   (level = 0.5)            Percent or fraction of peak
+	  (shifts = yes)            Compute shifts across the disp?\n
+	(dispaxis = 2)              Dispersion axis (long slit only)
+	(nspectra = 3)              Number of spec samples (ls only)
+	   (ndisp = 3)              Number of dispersion samples
+	   (slit1 = 50)             Lower slit edge
+	   (slit2 = 130)            Upper slit edge\n
+	 (logfile = "logfile")      Logfile
+	    (mode = "ql")
+    cl> specfocus @imlist
+    <Interactive graphics which is exited with the 'q' key>
+    SPECFOCUS: NOAO/IRAF V2.10EXPORT valdes Thu 19:41:41 17-Sep-92
+      Best avg focus at 206.6584 with avg width of 2.91 at 50% of peak
+
+      -- Average Over All Samples
+
+				     Image  Focus  Width
+				jdv011.imh   100.   3.78
+				jdv010.imh   150.   3.28
+				jdv009.imh   200.   2.95
+				jdv008.imh   250.   3.17
+				jdv007.imh   300.   3.41
+				jdv006.imh   350.   3.74
+				jdv005.imh   400.   4.16
+
+      -- Image jdv009.imh at Focus 200. --
+
+
+	    Width at 50% of Peak:
+
+			 Columns
+			   50-76      77-103    104-130 
+	       Lines  +---------------------------------
+	       2-267  |    2.93       2.58       2.74   
+	     268-533  |    3.17       2.76       2.89   
+	     534-799  |    3.77       2.23       3.50   
+
+	    Position Shifts Relative To Central Sample:
+
+			 Columns
+			   50-76      77-103    104-130 
+	       Lines  +---------------------------------
+	       2-267  |    0.68       0.00       0.18   
+	     268-533  |    0.64       0.00       0.13   
+	     534-799  |    0.92       0.00       0.16   
+.fi
+.ih
+SEE ALSO
+imexamine, implot, ranges, splot
+.endhelp