From 40e5a5811c6ffce9b0974e93cdd927cbcf60c157 Mon Sep 17 00:00:00 2001
From: Joe Hunkeler <jhunkeler@gmail.com>
Date: Tue, 11 Aug 2015 16:51:37 -0400
Subject: Repatch (from linux) of OSX IRAF

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 create mode 100644 noao/artdata/doc/mkechelle.hlp

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+.help mkechelle Mar93 noao.artdata
+.ih
+NAME
+mkechelle -- Make artificial echelle spectra
+.ih
+USAGE
+mkechelle images [clobber]
+.ih
+PARAMETERS
+.ls images
+List of echelle spectra to create or modify.
+.le
+.ls clobber (query)
+If an existing image is specified the clobber query parameter is used.
+Normally the parameter is not specified on the command line so that
+a query will be made for each image which exists.  Putting a value
+on the command line permanently overrides the query.  This should be
+done if the task is run in the background.
+.le
+.ls ncols = 512, nlines = 512, norders = 23
+For two dimensional spectra these parameters define the number of columns
+and lines in the final image and the maximum number of orders (there may be
+orders falling outside the image).  The dispersion is along the columns
+which is the second or line axis (dispersion axis is 2) so the number of
+columns is the number of pixels across the dispersion and the number of
+lines is the number of pixels along the dispersion per order.
+
+The extracted format turns the number of lines into the number columns
+and the number of orders is the number of lines; i.e the image
+has the specified number of extracted orders, one per image line,
+with the number of pixels along the dispersion specified by the
+\fInlines\fR parameter.  This is equivalent to what the \fBapextract\fR
+package would  produces for an extracted echelle format with an original
+dispersion axis of 2.  There is no check in this case for orders
+which might fall outside the two dimensional format; i.e. exactly
+the number of orders are created.
+.le
+.ls title = "Artificial Echelle Spectrum"
+Image title to be given to the spectra.  Maximum of 79 characters.
+.le
+.ls header = "artdata$stdheader.dat"
+Image or header keyword data file.  If an image is given then the image
+header is copied.  If a file is given then the FITS format cards are
+copied.  The data file consists of lines in FITS format with leading
+whitespace ignored.  A FITS card must begin with an uppercase/numeric
+keyword.  Lines not beginning with a FITS keyword such as comments or lower
+case are ignored.  The user keyword output of \fBimheader\fR is an
+acceptable data file.  See \fBmkheader\fR for further information.
+.le
+.ls list = no
+List the grating/instrument parameters?
+.le
+.ls make = yes
+Make the artificial spectra?  This is set to no if only the grating
+parameter listing is desired.
+.le
+.ls comments = yes
+Include comments recording task parameters in the image header?
+.le
+
+.ce
+FORMAT PARAMETERS
+.ls xc = INDEF, yc = INDEF
+The column and line position of the blaze peak in the reference order (see
+\fIorder\fR parameter.  If INDEF then the middle of the dimension is used.
+This allows setting the image center relative to the center of the echelle
+pattern.  As with the number of lines and columns the interpretation of
+these numbers relative to the image created depends on whether the format
+is extracted or not.
+.le
+.ls pixsize = 0.027
+Pixel size in millimeters.  This is used to convert the focal length
+and dispersion to pixels.  If INDEF then these parameters are
+assumed to be in pixels.
+.le
+.ls profile = "gaussian" (extracted|gaussian|slit)
+The order profile across the dispersion.  If the value is "extracted"
+then an extracted echelle format spectrum is produced.  Otherwise a
+two dimensional format with a gaussian or slit profile is produced.
+See \fBmk2dspec\fR for a discussion of the profile functions.
+.le
+.ls width = 5.
+If two dimensional echelle images are selected this parameter specifies
+the order profile full width at half maximum in pixels.  See \fBmk2dspec\fR
+for a fuller discussion.
+.le
+.ls scattered = 0.
+Scattered light peak flux per pixel.  A simple scattered light component
+may be included in the two dimensional format.  The scattered light has the
+blaze function shape of the central order along the dispersion and the
+crossdisperser blaze function shape across the dispersion with the peak
+value given by this parameter.  A value of zero indicates no scattered
+light component.
+.le
+
+.ce
+GRATING PARAMETERS
+
+Any of the following parameters may be specified as INDEF.  The missing
+values are resolved using the grating equations described in the
+DESCRIPTION section.  If it is not possible to resolve all the grating
+parameters but the order, wavelength, and dispersion are specified
+then a linear dispersion function is used.  Also in this case the
+extracted format will include dispersion information.
+.ls f = 590., cf = 590.
+Echelle and crossdisperser focal lengths in millimeters (if \fIpixsize\fR
+is given) or pixels.  Technically it is defined by the equation x = f * tan
+(theta) where x is distance from the optical axis on the detector and theta
+is the diffraction angle; i.e. it converts angular measures to millimeters
+or pixels on the detector.  If the focal length is specified as INDEF  it
+may be computed from the dispersion, which is required in this case, and
+the other parameters.
+.le
+.ls gmm = 31.6, cgmm = 226.
+Echelle and crossdisperser grating grooves per millimeter.  If specified as
+INDEF it may be computed from the order, which is required in this case,
+and the other parameters.
+.le
+.ls blaze = 63., cblaze = 4.53
+Echelle and crossdisperser blaze angles in degrees.  It is always specified or printed as a positive
+angle relative to the grating normal.  If specified as INDEF it is
+computed from the other parameters.
+.le
+.ls theta = 69., ctheta = -11.97
+Echelle and crossdisperser angles of incidence in degrees.  The angle of
+incidence must be in the plane perpendicular to face of the grating.  The
+angle of incidence may be specified relative to the grating normal or the
+blaze angle though it is always printed relative to the grating normal.  To
+specify it relative to the blaze angle add 360 degrees; for example to have
+an angle of 15 degrees less than the blaze angle specify 360 - 15 = 345.
+If the angle of incidence is specified as INDEF it is computed from the
+other parameters.
+.le
+.ls order = 112
+The central or reference echelle order for which the wavelength and
+dispersion are specified.  If specified as INDEF it will be computed from
+the grooves per mm, which is required in this case, and the other
+parameters.  In combination with the number of orders this defines the
+first and last orders.  The highest order is the central order plus
+the integer part of one half the number of orders.  However, the
+lowest order is constrained to be at least 1.  The
+reference order is also used in the definitions of \fIxc\fR and \fIyc\fR.
+.le
+.ls corder = 1
+The crossdisperser order for which the crossdisperser blaze wavelength and
+dispersion are specified.  If specified as INDEF it will be computed from
+the grooves per mm, which is required in this case, and the other
+parameters.
+
+If the order is zero then the other grating parameters are ignored and a
+prism-like dispersion is used with the property that the order spacing is
+constant.  Specifically the dispersion varies as the inverse of the
+wavelength with the \fIcwavelength\fR and \fIcdispersion\fR defining the
+function.
+.le
+.ls wavelength = 5007.49 cwavelength = 6700.
+Echelle and crossdisperser blaze wavelengths in Angstroms at the reference
+orders.  If specified as INDEF it will be computed from the other parameters.
+.le
+.ls dispersion = 2.61 cdispersion = 70.
+Echelle and crossdisperser blaze dispersions in Angstroms per millimeter
+(if \fIpixsize\fR is specified) or pixels.
+If specified as INDEF it will be computed from the focal length, which is
+required in this case, and the other parameters.
+.le
+
+.ce
+SPECTRA PARAMETERS
+.ls rv = 0.
+Radial velocity (km/s) or redshift, as selected by the parameter \fIz\fR,
+applied to line positions and continuum.  Velocities are converted to
+redshift using the relativistic relation 1+z = sqrt ((1+rv/c)/(1-rv/c)).
+Note the shift is not a shift in the dispersion parameters but in the
+underlying artificial spectrum.
+.le
+.ls z = no
+Is the velocity parameter a radial velocity or a redshift?
+.le
+.ls continuum = 1000.
+Continuum at the echelle blaze peak in the reference order.
+.le
+.ls temperature = 5700.
+Blackbody continuum temperature in Kelvin.  A value of 0 is used if
+no blackbody continuum is desired.  The intensity level is set by
+scaling to the continuum level at blaze peak reference point.
+.le
+
+.ls lines = ""
+List of spectral line files.  Spectral line files contain lines of rest
+wavelength, peak, and widths (see the DESCRIPTION section).
+The latter two parameters may be missing in which case they default to
+the task \fIpeak\fR and \fIsigma\fR parameters.  If no file or a new
+(nonexistent) file is specified then a number of random lines given by the
+parameter \fInlines\fR is generated.  If a new file name is specified then
+the lines generated are recorded in the file.  If the list of spectral
+line files is shorter than the list of input spectra, the last
+spectral line list file is reused.
+.le
+.ls nlines = 0
+If no spectral line file or a new file is specified then the task will
+generate this number of random spectral lines.  The rest wavelengths are
+uniformly random within the limits of the spectrum, the peaks are
+uniformly random between zero and the value of the \fIpeak\fR parameter
+and the width is fixed at the value of the \fIsigma\fR parameter.
+If a redshift is applied the rest wavelengths are shifted and repeated
+periodically.
+.le
+.ls peak = -0.5
+The maximum spectral line peak value when generating random lines or
+when the peak is missing from the spectral line file.
+This value is relative to the continuum unless the continuum is zero.
+Negative values are absorption lines and positive values are emission lines.
+.le
+.ls sigma = 1.
+The default line width as a gaussian sigma in Angstroms when generating
+random lines or when the width is missing from the spectral line file.
+.le
+.ls seed = 1
+Random number seed.
+.le
+
+PACKAGE PARAMETERS
+.ls nxsub = 10
+Number of pixel subsamples used in computing the gaussian spectral line
+profiles.
+.le
+.ls dynrange = 100000.
+The gaussian line profiles extend to infinity so a dynamic range, the ratio
+of the peak intensity to the cutoff intensity, is imposed to cutoff the
+profiles.
+.le
+.ih
+DESCRIPTION
+This task creates or adds to artificial extracted (one dimensional
+"echelle" format) or two dimensional echelle spectra.  The input spectrum
+(before modification by the spectrograph model) may be a combination of
+doppler shifted blackbody or constant continuum and emission and absorption
+gaussian profile spectral lines.  The lines may have randomly selected
+parameters or be taken from an input file.  Note that the parameters and
+method is similar to the task \fBmk1dspec\fR except that the input line list
+cannot specify a profile type and only Gaussian profiles are currently
+allowed.  The input spectrum is then
+separated out into echelle orders and either recorded as extracted one
+dimensional orders or convolved with a spatial profile and crossdispersed
+into a two dimensional image.  The properties of the echelle grating,
+crossdisperser, and instrumental configuration are modeled described
+later.
+
+If an existing image is specified the \fIclobber\fR parameter is used
+to determine whether to add the generated artificial echelle spectrum
+to the image.  Generally the clobber parameter is not specified on the
+command line to cause a query with the image name to be made for
+each image which already exists.  However, it is possible to put
+the clobber parameter on the command line to eliminate the query.
+This is appropriate for running the task in the background.
+
+There is \fIno\fR checking for consistency with an existing image;
+i.e. that it is an echelle image, whether it is an extracted format
+or a two dimensional spectrum, and what it's wavelength and order
+coverage is.  The only thing that happens is that the \fIncols\fR,
+\fInlines\fR, and \fInorders\fR parameters are replaced by the appropriate
+dimensions of the image with the choice between \fInlines\fR and
+\fInorders\fR made by the \fIprofile\fR parameter (as discussed below)
+and not by the format of the image.
+
+The created spectra are two dimensional, real datatype, images.  A title
+may be given and a set of header keywords be added by specifying an image
+or data file with the \fIheader\fR parameter (see also \fBmkheader\fR).  If
+a data file is specified lines beginning with FITS keywords are entered in
+the image header.  Leading whitespace is ignored and any lines beginning
+with words having lowercase and nonvalid FITS keyword characters are
+ignored.  In addition to this optional header, various parameters which
+occur during reduction of real echelle spectra, such a wavelength
+coordinates for extracted and dispersion corrected spectra, are added.
+Finally, comments may be added to the image header recording the task
+parameters and any information from the line file which are not line
+definitions.
+
+The creation of an artificial echelle spectra has three stages.  First a
+true spectrum is generated; i.e. the spectrum which arrives at the
+spectrograph.  The spectrum is then separated into orders and the
+dispersion and  blaze functions of the echelle and crossdisperser gratings
+(or crossdisperser prism) are applied.  Finally, if a two dimensional
+format is desired it is convolved by an spatial profile (either a gaussian
+or a broader slit-like profile) and the orders are placed as required by
+the crossdispersion relation.
+
+Generation of the model spectrum has three parts; defining a continuum,
+adding emission and absorption lines, and applying a doppler shift.  The
+continuum has two parameters; an intensity scale set by the \fIcontinuum\fR
+parameter and a shape set by the \fItemperature\fR parameter.  The
+intensity scale is set by defining the total, final, extracted intensity in
+a pixel at the blaze peak (rest) wavelength in the reference order; i.e. at
+the wavelength set by the \fIwavelength\fR parameter.  Note this means that
+the efficiency of the gratings at that wavelength is included.  The shape
+of the continuum may be either a blackbody if a positive temperature is
+specified or constant.
+
+Spectral lines are modeled by gaussian profiles of specified wavelength,
+peak, and sigma.  The lines are defined in a spectral line file or
+generated randomly.  A spectral line file consists of text lines giving
+rest wavelength, peak, and sigma.  The sigma or the sigma and peak may be
+absent in which case the parameters \fIsigma\fR and \fIpeak\fR will be
+used.  If peak values are missing random values between zero and the
+\fIpeak\fR value are generated.  Thus, a simple list of wavelengths or a
+list of wavelengths and peaks may be used.
+
+If no spectral line file is specified or a new (nonexistent) file is named
+then the number of random lines given by the parameter \fInlines\fR is
+generated.  The rest wavelengths are uniformly random within the wavelength
+range of the spectrum and extend periodically outside this range in the
+case of an applied velocity shift, the peaks are uniformly random between
+zero and the \fIpeak\fR parameter, and the widths are given by the
+\fIsigma\fR parameter.  If a new file is named then the parameters of the
+generated lines will be output.
+
+The peak values are taken relative to a positive continuum.  In other words
+the generated line profile is multiplied by the continuum (with a minimum
+of zero for fully saturated absorption lines).  If the continuum is less
+than or equal to zero, as in the case of an artificial arc spectrum or pure
+emission line spectrum, then the peak values are interpreted as absolute
+intensities.  Positive peak values produce emission lines and negative
+values produce absorption lines.  Odd results will occur if the continuum
+has both positive and zero or negative values.
+
+The width values are gaussian sigmas given in Angstroms.
+
+The underlying rest spectrum may be shifted.  This is used primarily for
+testing radial velocity measuring algorithms and is not intended as a
+complete model of redshift effects.  The observed wavelength coverage as
+defined by the grating parameters and number of orders is not changed by
+redshifting.  Input line wavelengths are specified at rest and then shifted
+into or out of the final spectrum.  To be realistic the line list should
+include wavelengths over a great enough range to cover all desired
+redshifts.  The peaks and sigma are also appropriately modified by a
+redshift.  As an example, if the redshift is 1 the lines will appear
+broader by a factor of 2 and the peaks will be down by a factor of 2 in
+order to maintain the same flux.
+
+The random line generation is complicated because one wants to have the
+same set of lines (for a given seed) observed at different redshifts.  What
+is done is that the specified number of random lines is generated within
+the observed wavelength interval taken at rest.  This set is then repeated
+periodical over all wavelengths.  A redshift will then shift these rest
+lines in to or out of the observed spectrum.  If the lines are output to a
+line file, they are given at rest.  \fBNote that this periodicity may be
+important in interpreting cross-correlation redshift tests for large shifts
+between template and object spectra.\fR
+
+The definitions of the continuum are also affected by a redshift.  The
+reference point for the continuum level and blackbody shape is the starting
+wavelength taken at rest.  Shifts will then modify the continuum level at
+the reference pixel appropriately.  In particular a large redshift will
+shift the blackbody in such a way that the flux is still given by the
+\fIcontinuum\fR parameter at the reference wavelength at rest.
+
+Once the input spectrum is defined it is modified by the effects of an
+echelle grating and crossdispersion.  This includes the dispersion relation
+between pixel and wavelength, the blaze response function of the gratings,
+and separation into orders.
+
+The primary reference for the model of the echelle grating (a
+crossdisperser grating also obeys this model) used in this task is "Echelle
+efficiencies: theory and experiment" by Schroeder and Hilliard in Applied
+Optics, Vol. 19, No. 16, 1980, p. 2833.  (The nomenclature below is similar
+to that paper except we use theta for alpha, their theta is theta - blaze,
+the reciprocal of the groove spacing which is the grooves per millimeter,
+and the dispersion per linear distance at the detector rather than per
+radian).  This task only treats the case where the incident beam is in the
+plane perpendicular to the grating face (gamma=0).  In this case the basic
+equation is
+
+.nf
+(1)	m * lambda = (sin(theta) + sin(beta)) / g
+.fi
+
+where m is the order, lambda the wavelength, g the grooves per wavelength
+unit, theta the angle of incidence to the grating normal, and beta the
+angle of diffraction to the normal.  The diffraction angle relative to that
+of the blaze maximum, psi, is given by
+
+.nf
+(2)	beta = psi + 2 * blaze - theta
+.fi
+
+where blaze is the blaze angle.  The diffraction angle psi is related to
+position on the detector, again measured from the blaze peak, by
+
+.nf
+(3)	x = f / pixsize * tan(psi)
+.fi
+
+where f is the effective focal length (as defined by this equation) and
+pixsize is the pixel size in millimeters that converts the detector
+positions to pixels.  If a pixel size is not specified then f will be
+taken as being in pixels.
+
+The second basic equation is the diffraction pattern or blaze response
+given by
+
+.nf
+(5)	I = I0 * (sin(delta) / delta) ** 2
+(6)	delta = 2 * pi / lambda * (cos(theta) / g) / cos(epsilon) *
+		sin(psi/2) * cos(epsilon-psi/2)
+(7)	epsilon = theta - blaze
+.fi
+
+where epsilon is the angle between the blaze angle and the angle of
+incidence (the theta of  Shroeder and Hilliard).  When theta = blaze, (6)
+simplifies to
+
+.nf
+(6a)	delta = pi / lambda * (cos (blaze) / g) * sin (psi)
+.fi
+
+As discussed by Schroeder and Hilliard, the relative intensity at the blaze
+peak, I0, must be reduced by the fraction of light at the same wavelength
+as the blaze peak which is diffracted into other orders.  Furthermore at
+some diffraction angles the light is reflected off the second face of the
+grating giving a different effective diffraction angle to be used in (6).
+This computation is done by the task giving a variation in relative blaze
+response with order and reproducing the calculations of Schroeder and
+Hilliard.  The absolute normalization, including the crossdisperser blaze
+function if any, is such that the response at the blaze peak of the
+reference order is unity.  This insures that specified continuum level at
+the reference wavelength is produced.
+
+At the blaze maximum psi = x = 0 and the wavelength and dispersion per
+millimeter on the detector are given by (1) and the derivative of (1) with
+respect to x:
+
+.nf
+(8)	wavelength = 1E7*(sin(theta)+sin(2*blaze-theta))/(gmm*order)
+(9)	dispersion = 1E7*cos(2*blaze-theta)/(gmm*order*f/pixsize)
+.fi
+
+The variable names are the same as the parameters in this task.   In
+particular, gmm is the echelle grooves per millimeter with the factors of
+1E7 (10 to the seventh power) to convert to Angstroms, the factor of f /
+pixsize to convert the dispersion to per pixel, and order is the reference
+order for the wavelength and dispersion.
+
+The \fBmkechelle\fR task provides different ways to define the parameters.
+If there is insufficient information to determine all the grating
+parameters but the wavelength, dispersion, order are specified then
+a simplified grating equation is used which is linear with pixel
+position.  The approximation is that tan(psi) = sin(psi) = psi so
+that
+
+.nf
+(9)	lambda = (order * wavelength + dispersion * x) / m
+               = (a + b * x) / m
+(10)	delta  = pi * order * dispersion / lambda * x
+               =  c / lambda * x
+.fi
+
+Also in this case the extracted format (described later) includes
+wavelength information in the header so that the spectra appear as fully
+dispersion corrected.
+
+If there are at least five of the seven grating parameters specified
+then equations (8) and (9) are used to determine
+unspecified parameters or to override parameters if the equations are
+overspecified.  For example, suppose the grooves per millimeter is known
+but not the blaze angle or focal length.  Then the wavelength and
+dispersion at the reference order are used to compute these quantities.
+
+The full set of grating parameters derived and used to create the spectra
+are documented in the image header if the \fIcomments\fR parameter is
+specified.  Also the \fIlist\fR parameter may be set to print the grating
+parameters and the \fImake\fR parameter may be set to no to check the
+grating parameters without making the spectra.
+
+The crossdisperser grating parameters are treated exactly as above except,
+since only one order is used, the relative blaze efficiency is not
+computed.
+
+There is a variant on the crossdispersion to allow a prism-like separation
+of the echelle orders.  If the crossdispersion grating order, \fIcorder\fR
+is set to zero then the other grating parameters are ignored and a
+prism-like dispersion is used with the property that the order spacing is
+constant.  Specifically the dispersion varies as the inverse of the
+wavelength with the \fIcwavelength\fR and \fIcdispersion\fR defining the
+function.  There is no crossdisperser blaze function in this case either;
+i.e. the relative intensities between orders is solely due to the echelle
+grating blaze response.
+
+There is an interesting effect which follows from the above equations but
+which is not obvious at first glance.  When the full grating equation is
+used the dispersion varies with wavelength.  This means the size of a pixel
+in wavelength varies and so the flux in a pixel changes.  The effect is
+such that the order intensity maximum shifts to the blue from the blaze peak
+because the pixel width in Angstroms increases to the blue faster, for a
+while, than the blaze response decreases.
+
+Once the spectrum has been separated into orders, modified by the
+grating blaze functions, and sampled into pixels in the dispersion
+direction it may be output as an extracted "echelle" format spectrum.
+This occurs when the spatial profile is specified as "extracted".
+The keywords added by the \fBapextract\fR package are included in
+the image header.  If the dispersion model is linear
+the keywords are the same as those produced by the dispersion
+correction task \fBecdispcor\fR.
+
+If the spatial profile is specified as "gaussian" or "slit" then the
+orders are convolved by the profile function and the crossdispersion
+relation is used to determine where the order falls at each wavelength.
+The spatial profiles are defined by the formulas:
+
+.nf
+    gaussian:   I(x) = exp (-ln(2) * (2*(x-xc(w))/width)**2)
+        slit:   I(x) = exp (-ln(2) * (2*(x-xc(w))/width)**10)
+.fi
+
+where x is the spatial coordinate, xc(w) is the order center at
+wavelength w, and width is the full width at half maximum specified by
+the parameter of that name.  The "gaussian" profile
+is the usual gaussian specified in terms of a FWHM.  The "slit"
+profile is one which is relatively flat and then rapidly drops
+to zero.  The profile is normalized to unit integral so that
+the total flux across the profile is given by the scaled
+1D spectrum flux.  The profile is fully sampled and then binned to
+the pixel size to correctly include sampling effects as a function
+of where in a pixel the order center falls.
+
+Note that in this model the orders are always tilted with respect
+to the columns and constant wavelength is exactly aligned with the
+image lines.
+.ih
+EXAMPLES
+1. Create an absorption spectrum with blackbody continuum and scattered
+light using the default grating parameters then add noise.
+
+.nf
+	cl> mkechelle ex1 nrand=100 scat=100.
+	cl> mknoise ex1 gain=2 rdnoise=5 poisson+
+.fi
+
+2. Create an arc spectrum using the line list noao$lib/onedstds/thorium.dat.
+
+.nf
+	cl> mkechelle ex2 cont=10 temp=0 \
+	lines=noao$lib/onedstds/thorium.dat peak=1000 sigma=.05
+.fi
+
+Note that the line intensities are random and not realistic.  The peak
+intensities range from 0 to 1000 times the continuum or 10000.
+
+3. Create an extracted version of example1.
+
+.nf
+	cl> mkechelle ex1.ec prof=extracted nrand=100 scat=100.
+	cl> mknoise ex1.ec gain=2 rdnoise=5 poisson+
+.fi
+
+Note that the noise is different and greater than would be the case with
+extracting the orders of example 1 because the noise is not summed
+over the order profile but is added after the fact.
+
+4. Create an extracted and dispersion corrected version of example1.
+
+.nf
+	cl> mkechelle ex1.ec prof=extracted nrand=100 scat=100. \
+	gmm=INDEF blaze=INDEF theta=INDEF
+	Echelle grating: Using linear dispersion
+	Warning: Insufficient information to resolve grating parameters
+	cl> mknoise ex1.ec gain=2 rdnoise=5 poisson+
+.fi
+
+The warning is expected.  By not specifying all the parameters needed to
+fully model an echelle grating the default action is to use a linear
+dispersion in each order and to set the image header dispersion
+information.  When a complete grating model is specified, as in example 3,
+the extracted spectrum is not given dispersion information so that the
+nonlinear behavior of the dispersion can be applied by \fBecidentify\fR and
+\fBdispcor\fR.  As with example 3, the noise is different since it is added
+after extraction and dispersion correction.
+.ih
+REVISIONS
+.ls MKECHELLE V2.10.3
+The task was updated to produce the current coordinate system format.
+.le
+.ih
+SEE ALSO mknoise, mk1dspec, mk2dspec, mkheader, astutil.gratings
+.endhelp
-- 
cgit 

