From fa080de7afc95aa1c19a6e6fc0e0708ced2eadc4 Mon Sep 17 00:00:00 2001
From: Joseph Hunkeler <jhunkeler@gmail.com>
Date: Wed, 8 Jul 2015 20:46:52 -0400
Subject: Initial commit

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+.help ccmap Jan01 images.imcoords
+.ih
+NAME
+ccmap -- compute plate solutions using matched pixel and celestial coordinate
+lists
+.ih
+USAGE
+ccmap input database
+.ih
+PARAMETERS
+.ls input
+The input text files containing the pixel and celestial coordinates of
+points in the input images. The coordinates are listed one per line with x, y,
+ra / longitude, and dec / latitude in the columns specified by the
+\fIxcolumn\fR, \fIycolumn\fR, \fIlngcolumn\fR, and \fIlatcolumn\fR parameters
+respectively.  Whether all files are combined to produce one solution or
+each file produces a separate solution depends on whether there is a
+matching list of output \fIsolutions\fR names or \fIresults\fR files.
+.le
+.ls database
+The text database file where the computed plate solutions are stored.
+.le
+.ls solutions = ""
+An optional list of plate solution names. If there are multiple input
+coordinate files and no name or a single name is specified then the
+input coordinates are combined to produce a single solution.  Otherwise
+the list must match the number of input coordinate files.  If no names are
+supplied then the database records are assigned the names of the input
+images \fIimages\fR, or the names of the coordinate files \fIinput\fR.
+In the case of multiple coordinate files the first image or input is used.
+.le
+.ls images = ""
+The images associated with the input coordinate files. The number of images
+must be zero or equal to the number of input coordinate files. If an input
+image exists and the \fIupdate\fR parameter is enabled, the image wcs will
+be created from the linear component of the computed plate solution
+and written to the image header.
+.le
+.ls results = ""
+Optional output files containing a summary of the results including a
+description of the plate geometry and a listing of the input coordinates,
+the fitted coordinates, and the fit residuals. The number of
+results files must be zero, one or equal to the number of input files. If
+results is "STDOUT" the results summary is printed on the standard output.
+If there are multiple input coordinate files and zero or one output is
+specified then the input coordinates are combined to produce a single solution.
+.le
+.ls xcolumn = 1, ycolumn = 2, lngcolumn = 3, latcolumn = 4
+The input coordinate file columns containing the x, y, ra / longitude and
+dec / latitude values.
+.le
+.ls xmin = INDEF, xmax = INDEF, ymin = INDEF, ymax = INDEF
+The range of x and y pixel coordinates over which the computed coordinate
+transformation is valid. These limits should be left at INDEF or set to
+the values of the column and row limits of the input images, e.g xmin = 1.0,
+xmax = 512, ymin= 1.0, ymax = 512 for a 512 x 512 image.  If xmin, xmax, ymin,
+or ymax are undefined, they are set to the minimum and maximum x and y
+pixels values in \fIinput\fR.
+.le
+.ls lngunits = "", latunits = ""
+The units of the input ra / longitude and dec / latitude coordinates. The
+options are "hours", "degrees", and "radians" for ra / longitude, and
+"degrees" and "radians" for dec / latitude. If the lngunits and latunits
+are undefined they default to the preferred units for the coordinate system
+specified by \fIinsystem\fR, e.g. "hours" and "degrees" for equatorial
+systems, and "degrees" and "degrees" for ecliptic, galactic, and
+supergalactic systems.
+.le
+.ls insystem = "j2000"
+The input celestial coordinate system. The \fIinsystem\fR parameter
+sets the preferred units for the input celestial coordinates,
+tells CCMAP how to transform the celestial coordinates of the reference
+point from the reference point coordinate system to the input coordinate
+system, and sets the correct values of the image header keywords CTYPE,
+RADECSYS, EQUINOX, and MJD-WCS if the image header wcs is updated. The 
+systems of most interest to users are "icrs", "j2000", and "b1950" which
+stand for the ICRS J2000.0, FK5 J2000.0 and FK4 B1950.0 celestial coordinate
+systems respectively.  The full set of options are the following:
+
+.ls equinox [epoch]
+The equatorial mean place post-IAU 1976 (FK5) system if equinox is a
+Julian epoch, e.g. J2000.0 or 2000.0, or the equatorial mean place
+pre-IAU 1976 system (FK4) if equinox is a Besselian epoch, e.g. B1950.0
+or 1950.0. Julian equinoxes are prefixed by a J or j, Besselian equinoxes
+by a B or b. Equinoxes without the J / j or B / b prefix are treated as
+Besselian epochs if they are < 1984.0, Julian epochs if they are >= 1984.0.
+Epoch is the epoch of the observation and may be a Julian
+epoch, a Besselian epoch, or a Julian date. Julian epochs
+are prefixed by a J or j, Besselian epochs by a B or b.
+Epochs without the J / j or B / b prefix default to the epoch type of
+equinox if the epoch value <= 3000.0, otherwise epoch is interpreted as
+a Julian date.  If undefined epoch defaults to equinox.
+.le
+.ls icrs [equinox] [epoch]
+The International Celestial Reference System where equinox is
+a Julian or Besselian epoch e.g. J2000.0  or B1980.0.
+Equinoxes without the J / j or B / b prefix are treated as Julian epochs.
+The default value of equinox is J2000.0.
+Epoch is a Besselian epoch, a Julian epoch, or a Julian date.
+Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
+Epochs without the J / j or B / b prefix default to Julian epochs
+if the epoch value <= 3000.0, otherwise epoch is interpreted as
+a Julian date.  If undefined epoch defaults to equinox.
+.le
+.ls fk5 [equinox] [epoch] 
+The equatorial mean place post-IAU 1976 (FK5) system where equinox is
+a Julian or Besselian epoch e.g. J2000.0  or B1980.0.
+Equinoxes without the J / j or B / b prefix are treated as Julian epochs.
+The default value of equinox is J2000.0.
+Epoch is a Besselian epoch, a Julian epoch, or a Julian date.
+Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
+Epochs without the J / j or B / b prefix default to Julian epochs
+if the epoch value <= 3000.0, otherwise epoch is interpreted as
+a Julian date.  If undefined epoch defaults to equinox.
+.le
+.ls fk4 [equinox] [epoch]
+The equatorial mean place pre-IAU 1976 (FK4) system where equinox is a
+Besselian or Julian epoch e.g. B1950.0  or J2000.0,
+and epoch is the Besselian epoch, the Julian epoch, or the Julian date of the
+observation.
+Equinoxes without the J / j or B / b prefix are treated
+as Besselian epochs. The default value of equinox is B1950.0. Epoch
+is a Besselian epoch, a Julian epoch, or a Julian date.
+Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
+Epochs without the J / j or B / b prefix default to Besselian epochs
+if the epoch value <= 3000.0, otherwise epoch is interpreted as
+a Julian date.  If undefined epoch defaults to equinox.
+.le
+.ls noefk4 [equinox] [epoch]
+The equatorial mean place pre-IAU 1976 (FK4) system but without the E-terms
+where equinox is a Besselian or Julian epoch e.g. B1950.0 or J2000.0,
+and epoch is the Besselian epoch, the Julian epoch, or the Julian date of the
+observation.
+Equinoxes without the J / j or B / b prefix are treated
+as Besselian epochs. The default value of equinox is B1950.0.
+Epoch is a Besselian epoch, a Julian epoch, or a Julian date.
+Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
+Epochs without the J / j or B / b prefix default to Besselian epochs
+if the epoch value <= 3000.0, otherwise epoch is interpreted as
+a Julian day.  If undefined epoch defaults to equinox.
+.le
+.ls apparent epoch 
+The equatorial geocentric apparent place post-IAU 1976 system where
+epoch is the epoch of observation.
+Epoch is a Besselian epoch, a Julian epoch or a Julian date.
+Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
+Epochs without the J / j or B / b prefix default to Besselian
+epochs if the epoch value < 1984.0, Julian epochs
+if the epoch value <= 3000.0, otherwise epoch is interpreted as
+a Julian date.
+.le
+.ls ecliptic epoch
+The ecliptic coordinate system where epoch is the epoch of observation.
+Epoch is a Besselian epoch, a Julian epoch, or a Julian date.
+Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
+Epochs without the J / j or B / b prefix default to Besselian epochs
+if the epoch values < 1984.0, Julian epochs
+if the epoch value <= 3000.0, otherwise epoch is interpreted as
+a Julian day.
+.le
+.ls galactic [epoch]
+The IAU 1958 galactic coordinate system.
+Epoch is a Besselian epoch, a Julian epoch or a Julian date.
+Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
+Epochs without the J / j or B / b prefix default to Besselian
+epochs if the epoch value < 1984.0, Julian epochs
+if the epoch value <= 3000.0, otherwise epoch is interpreted as
+a Julian date. The default value of epoch is B1950.0.
+.le
+.ls supergalactic [epoch]
+The deVaucouleurs supergalactic coordinate system.
+Epoch is a Besselian epoch, a Julian epoch or a Julian date.
+Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
+Epochs without the J / j or B / b prefix default to Besselian
+epochs if the epoch value < 1984.0, Julian epochs
+if the epoch value <= 3000.0, otherwise epoch is interpreted as
+a Julian date. The default value of epoch is B1950.0.
+.le
+
+In all the above cases fields in [] are optional with the defaults as
+described. The epoch field for the icrs, fk5, galactic, and supergalactic
+coordinate systems is only used if the input coordinates are in the
+equatorial fk4, noefk4, fk5, or icrs systems and proper motions are supplied.
+Since CCMAP does not currently support proper motions these fields are
+not required.
+.le
+
+.ls refpoint = "coords"
+The definition of the sky projection reference point in celestial coordinates,
+e.g. the tangent point in the case of the usual tangent plane projection.
+The options are:
+.ls coords
+The celestial coordinates of the reference point are set to the mean of the 
+input celestial coordinates, e.g. the mean of ra / longitude and dec /
+latitude coordinates. If the true tangent point is reasonably close to
+the center of the input coordinate distribution and the input is not
+too large, this approximation is reasonably accurate.
+.le
+.ls user
+The values of the keywords \fIlngref\fR, \fIlatref\fR, \fIrefsystem\fR,
+\fIlngrefunits\fR, and \fIlatrefunits\fR are used to determine the celestial
+coordinates of the reference point.
+.le
+.le
+.ls xref = "INDEF", yref = "INDEF"
+The reference pixel may be specified as a value or image header keyword.
+In the latter case a reference image must be specified.  By specifying
+the reference pixel the solution will be constrained to putting the
+reference coordinate at that point.
+.le
+.ls lngref = "INDEF", latref = "INDEF"
+The ra / longitude and dec / latitude of the reference point(s).  Lngref
+and latref may be numbers, e.g 13:20:42.3 and -33:41:26 or keywords for the
+appropriate parameters in the image header, e.g. RA/DEC or CRVAL1/CRVAL2.
+Each parameter may be a list to apply different reference points to
+each input coordinate list.  If lngref and latref are undefined then
+the position of the reference point defaults to the mean of the input
+coordinates.
+.le
+.ls refsystem = "INDEF"
+The celestial coordinate system of the reference point. Refsystem may
+be any one of the options listed under the \fIinsystem\fR parameter, e.g.
+"b1950", or an image header keyword containing the epoch of the observation
+in years, e.g. EPOCH for NOAO data. In the latter case the coordinate system is
+assumed to be equatorial FK4 at equinox EPOCH. If refsystem is undefined
+the celestial coordinate system of the reference point defaults to the
+celestial coordinate system of the input coordinates \fIinsystem\fR.
+.le
+.ls lngrefunits = "", latrefunits = ""
+The units of the reference point celestial  coordinates. The options
+are "hours", "degrees", and "radians" for the ra / longitude coordinates,
+and "degrees" and "radians" for the dec /latitude coordinates. 
+If lngunits and latunits are undefined they default to the  units of the
+input coordinate system.
+.le
+.ls projection = "tan"
+The sky projection geometry. The most commonly used projections in astronomy
+are "tan", "arc", "sin", and "lin". Other supported  standard projections
+are "ait", "car","csc", "gls", "mer", "mol", "par", "pco", "qsc", "stg",
+"tsc", and "zea". A new experimental function "tnx", a combination of the
+tangent plate projection and polynomials, is also available.
+.le
+.ls fitgeometry = "general"
+The plate solution geometry to be used. The options are the following, where
+xi and eta refer to the usual standard coordinates used in astrometry.
+.ls shift
+Xi and eta shifts only are fit.
+.le
+.ls xyscale
+Xi and eta shifts and x and y magnification factors in " / pixel are fit.
+Axis flips are allowed for.
+.le
+.ls rotate
+Xi and eta shifts and a rotation angle are fit. Axis flips are allowed for.
+.le
+.ls rscale
+Xi and eta shifts, a magnification factor in " / pixel assumed to be the same
+in x and y, and a rotation angle are fit. Axis flips are allowed for.
+.le
+.ls rxyscale
+Xi and eta shifts, x and y magnifications factors in " / pixel, and a rotation
+angle are fit.  Axis flips are allowed for.
+.le
+.ls general
+A polynomial of arbitrary order in x and y is fit. A linear term and a
+distortion term are computed separately. The linear term includes a xi and eta
+shift, an x and y scale factor in " / pixel, a rotation and a skew.  Axis
+flips are also allowed for in the linear portion of the fit. The distortion
+term consists of a polynomial fit to the residuals of the linear term. By
+default the distortion term is set to zero.
+.le
+
+For all the fitting geometries except "general" no distortion term is fit,
+i.e. the x and y polynomial orders are assumed to be 2 and the cross term
+switches are assumed to be set to "none", regardless of the values of the
+\fIxxorder\fR, \fIxyorder\fR, \fIxxterms\fR, \fIyxorder\fR, \fIyyorder\fR
+and \fIyxterms\fR parameters set by the user.
+.le
+.ls function = "polynomial"
+The type of analytic coordinate surface to be fit. The options are the
+following.
+.ls legendre
+Legendre polynomials in x and y.
+.le
+.ls chebyshev
+Chebyshev polynomials in x and y.
+.le
+.ls polynomial
+Power series polynomials in x and y.
+.le
+.le
+.ls xxorder = 2, xyorder = 2,  yxorder = 2, yyorder = 2
+The order of the polynomials in x and y for the xi and eta fits respectively.
+The default order and cross term settings define the linear term in x
+and y, where the 6 coefficients can be interpreted in terms of an xi and eta
+shift, an x and y scaling in " / pixel, and rotations of the x and y axes.
+The "shift", "xyscale", "rotation", "rscale", and "rxyscale", fitting geometries
+assume that the polynomial order parameters are 2 regardless of the values
+set by the user. If any of the order parameters are higher than 2 and
+\fIfitgeometry\fR is "general", then a distortion surface is fit to the
+residuals from the linear portion of the fit.
+.le
+.ls xxterms = "half", yxterms = "half"
+The options are:
+.ls none
+The individual polynomial terms contain powers of x or powers of y but not
+powers of both.
+.le
+.ls half
+The individual polynomial terms contain powers of x and powers of y, whose
+maximum combined power is MAX (xxorder - 1, xyorder - 1) for the xi fit and
+MAX (yxorder - 1, yyorder - 1) for the eta fit. This is the recommended
+option for higher order plate solutions. 
+.le
+.ls full
+The individual polynomial terms contain powers of x and powers of y, whose
+maximum combined power is MAX (xxorder - 1 + xyorder - 1) for the xi fit and
+MAX (yxorder - 1 + yyorder - 1) for the eta fit.
+.le
+
+The "shift", "xyscale", "rotation",
+"rscale", and "rxyscale" fitting geometries, assume that the
+cross term switches are set to "none" regardless of the values set by the user.
+If either of the cross-terms parameters is set to "half" or "full" and
+\fIfitgeometry\fR is "general" then a distortion surface is fit to the
+residuals from the linear portion of the fit.
+.le
+.ls maxiter = 0
+The maximum number of rejection iterations. The default is no rejection.
+.le
+.ls reject = INDEF
+The rejection limit in units of sigma.
+.le
+.ls update = no
+Update the world coordinate system in the input image headers ?
+The required numerical quantities represented by the keywords CRPIX,
+CRVAL, and CD are computed from the linear portion of the plate solution,
+The values of the keywords CTYPE, RADECSYS, EQUINOX, and MJD-WCS
+are set by the \fIprojection\fR and \fIinsystem\fR parameters. As there
+is currently no standard mechanism for storing the higher order plate solution
+terms if any in the image header wcs, these terms are currently ignored
+unless the projection function is the experimental function "tnx". The "tnx"
+function is not FITS compatible and can only be understood by IRAF. Any existing
+image wcs represented by the above keywords is overwritten during the update.
+.le
+.ls pixsystem = "logical"
+The input pixel coordinate system. The options are:
+.ls logical
+The logical pixel coordinate system is the coordinate system of the image
+pixels on disk. Since most users measure the pixel coordinates of objects
+in this system, "logical" is the system of choice for most applications.
+.le
+.ls physical
+The physical coordinate system is the pixel coordinate system of the
+parent image if any. This option may be useful for users working on images
+that are pieces of a larger mosaic.
+.le
+
+The choice of pixsystem has no affect on the fitting process, but does 
+determine how the image header wcs is updated.
+.le
+.ls verbose = yes
+Print detailed messages about the progress of the task on the standard output ?
+.le
+.ls interactive = yes
+Compute the plate solution interactively ?
+In interactive mode the user may interact with the fitting process, e.g.
+change the order of the fit, reject points, display the data and refit, etc.
+.le
+.ls graphics = "stdgraph"
+The graphics device.
+.le
+.ls cursor = ""
+The graphics cursor.
+.le
+.ih
+DESCRIPTION
+
+CCMAP computes the plate solution for an image or set of images using lists
+of matched pixel and celestial coordinates. The celestial coordinates
+are usually equatorial coordinates, but may also be ecliptic, galactic,
+or supergalactic coordinates.  The input coordinate files \fIinput\fR must
+be text file tables whose columns are delimited by whitespace. The pixel
+and celestial coordinates are listed in input, one per line with  x, y,
+ra / longitude, and dec / latitude in columns \fIxcolumn\fR, \fIycolumn\fR,
+\fIlngcolumn\fR, and \fIlatcolumn\fR respectively.
+
+The \fIxmin\fR, \fIxmax\fR, \fIymin\fR and \fIymax\fR parameters define
+the region of validity of the fit in the pixel coordinate system. They should
+normally either be left set to INDEF, or set to the size of input images
+\fIimages\fR if any, e.g. xmin= 1.0, xmax= 512.0, ymin = 1.0, ymax = 512.0
+for a 512 square image. If set these parameters are also used to reject out
+of range pixel data before the actual fitting is done.
+
+The \fIlngunits\fR and \fIlatunits\fR parameters set the units of the input
+celestial coordinates. If undefined lngunits and latunits assume sensible
+defaults for the input celestial coordinate system set by the \fIinsystem\fR
+parameter, e.g. "hours" and "degrees" for equatorial coordinates and "degrees"
+and "degrees" for galactic coordinates. The input celestial coordinate system
+must be one of the following: equatorial, ecliptic, galactic, or supergalactic.
+The equatorial coordinate systems must be one of: 1) FK4, the mean place
+pre-IAU 1976 system, 2) FK4-NO-E, the same as FK4 but without the E-terms,
+3) FK5, the mean place post-IAU 1976 system, 4) GAPPT, the geocentric apparent
+place in the post-IAU 1976 system.
+
+The plate solution computed by CCMAP has the following form, where x and y
+are the pixel coordinates of points in the input image and xi and eta are the
+corresponding standard coordinates in units of " / pixel.
+
+.nf
+     xi = f (x, y)
+    eta = g (x, y)
+.fi
+
+The standard coordinates xi and eta are computed from the input celestial
+coordinates using the sky projection geometry \fIprojection\fR and
+the celestial coordinates of the projection reference point set by
+the user. The default projection is the tangent plane or gnomonic
+projection commonly used in optical astronomy. The projections most commonly
+used in astronomy are "sin" (the orthographic projection, used in radio
+aperture synthesis), "arc" (the zenithal equidistant projection, widely
+used as an approximation for Schmidt telescopes), and "lin" (linear).
+Other supported projections are "ait", "car", "csc", "gls", "mer", "mol",
+"par", "pco", "qsc", "stg", "tsc", and "zea". The experimental projection
+function "tnx" combines the "tan" projection with a polynomial fit
+to the residuals can be used to represent more complicated distortion
+functions.
+
+There are two modes in which this task works with multiple input
+coordinate lists.  In one case each input list and possible associated
+image is treated independently and produce separate solutions.  To
+select this option requires specifying a matching list of solution
+names or output results files.  Note that this can also be simply done
+by running the task multiple times with a single input list each time.
+
+In the second mode data from multiple input lists are combined to
+produce a single solution.  This is useful when multiple exposures are
+taken to define a higher quality astrometric solution.  This mode is
+selected when there are multiple input lists, and possibly associated
+images, and no solution name or a single solution name is specified.
+
+When combining input data each set of coordinates may have different
+reference points which can be specified either as a list or by
+reference to image header keywords.  The different reference points
+are used to convert each set of coordinates to the same coordinate
+frame.  Typically this occurs when a set of exposures, each with the
+same coordinate reference pixel, has slightly different pointing as
+defined by the coordinate reference value.  These different points
+result from a dither and can be useful to more completely sample the
+image pixel space.  In other words, astrometric reference stars can be
+moved around the images to produce many more fitting points than occur
+with a single exposure. The key point to this process is that the
+shifts are mapped by the reference points of the pointing and the
+standard coordinates are independent of the pointing.
+
+A particular feature primarily intending for combining multiple
+exposures, but applies to single exposures as well, is an adjustment to
+the specified tangent point value based on the image WCS.  When images,
+reference pixels, and reference coordinates are all defined and the
+images contain a celestial WCS the following computation is performed.
+The reference information replaces the WCS tangent point values, though
+typically the initial reference information is specified as the tangent
+point, and the updated WCS is used to evaluate celestial coordinates
+from the input pixel coordinates. The average difference between the WCS
+evaluated coordinates and the input celestial coordinates is computed.
+This difference is applied to the reference point prior to the standard
+coordinate plate solution calculation.  In other words, the reference
+point is tweaked in the initial image WCS to make it agree on average with
+the input reference coordinates.  If one updates the WCS of the images by
+the plate solution and the repeats the plate solution, particularly when
+using multiple exposures, an iterative convergence to a self-consistent
+WCS of both the tangent point and plate solution can be obtained.
+
+Several polynomial cross terms options are available. Options "none", 
+"half", and "full" are illustrated below for a quadratic polynomial in
+x and y.
+
+.nf
+xxterms = "none", xyterms = "none"
+xxorder = 3, xyorder = 3, yxorder = 3, yyorder = 3
+
+    xi = a11 + a21 * x + a12 * y +
+         a31 * x ** 2 + a13 * y ** 2
+   eta = a11' + a21' * x + a12' * y +
+         a31' * x ** 2 + a13' * y ** 2
+
+xxterms = "half", xyterms = "half"
+xxorder = 3, xyorder = 3, yxorder = 3, yyorder = 3
+
+    xi = a11 + a21 * x + a12 * y +
+         a31 * x ** 2 + a22 * x * y + a13 * y ** 2
+   eta = a11' + a21' * x + a12' * y +
+         a31' * x ** 2 + a22' * x * y + a13' * y ** 2
+
+xxterms = "full", xyterms = "full"
+xxorder = 3, xyorder = 3, yxorder = 3, yyorder = 3
+
+    xi = a11 + a21 * x + a31 * x ** 2 +
+         a12 * y + a22 * x * y +  a32 * x ** 2 * y +
+         a13 * y ** 2 + a23 * x *  y ** 2 + a33 * x ** 2 * y ** 2
+   eta = a11' + a21' * x + a31' * x ** 2 +
+         a12' * y + a22' * x * y +  a32' * x ** 2 * y +
+         a13' * y ** 2 + a23' * x *  y ** 2 + a33' * x ** 2 * y ** 2
+.fi
+
+If \fIrefpoint\fR is "coords", then the sky projection reference point is set
+to the mean of the input celestial coordinates. For images where the true
+reference point is close to the center of the input coordinate distribution,
+this definition is adequate for many purposes. If \fIrefpoint\fR is "user",
+the user may either set the celestial coordinates of the reference
+point explicitly, e.g. \fIlngref\fR = 13:41:02.3 and \fIlatref\fR = -33:42:20,
+or point these parameters to the appropriate keywords in the input image
+header, e.g. \fIlngref\fR = RA, \fIlatref\fR = DEC for NOAO image data.
+If undefined the celestial coordinate system of the reference point
+\fIrefsystem\fR defaults to the celestial coordinate system of the input
+coordinates, otherwise it be any of the supported celestial coordinate
+systems described above. The user may also set \fIrefsystem\fR to the
+image header keyword containing the epoch of the celestial reference point
+coordinates in years, e.g. EPOCH for NOAO data. In this case the
+reference point coordinates are assumed to be equatorial FK4 coordinates at the
+epoch specified by EPOCH. The units of the reference point celestial
+coordinates are specified by the \fIlngrefunits\fR and \fIlatrefunits\fR
+parameters. Lngrefunits and latrefunits default to the values of the input
+coordinate units if undefined by either the user or the \fIrefsystem\fR
+parameter. ONCE DETERMINED THE REFERENCE POINT CANNOT BE RESET DURING
+THE FITTING PROCESS.
+
+The \fIxref\fR and \fIyref\fR parameters may be used to constrain the
+solution to putting the reference coordinate at the reference pixel.
+Effectively what this does is fix the zero-th order coefficient in the
+linear part of the solution.  If a reference pixel is not specified the
+solution will produce a point determined from the zero-th order
+constant coefficient.  This may not be what is expected based on
+the specified reference celestial coordinate.
+
+The fitting functions f and g are specified by the \fIfunction\fR parameter
+and may be power series polynomials, Legendre polynomials, or Chebyshev
+polynomials of order \fIxxorder\fR and \fIxyorder\fR in x and \fIyxorder\fR
+and \fIyyorder\fR in y. Cross-terms are optional and are turned on and
+off by setting the \fIxxterms\fR and \fIxyterms\fR parameters. If the
+\fBfitgeometry\fR parameter is anything other than "general", the order
+parameters assume the value 2 and the cross-terms switches assume the value
+"none", regardless of the values set by the user. All computation are done in
+double precision. Automatic pixel rejection may be enabled by setting
+\fImaxiter\fR > 0 and \fIreject\fR to a  positive value, usually something
+in the range 2.5-5.0.
+
+CCMAP may be run interactively by setting \fIinteractive\fR to "yes" and
+inputting commands by the use of simple keystrokes. In interactive mode the
+user has the option of changing the fitting parameters and displaying the
+data and fit graphically until a satisfactory fit has been achieved. The
+keystroke commands are listed below.
+
+.nf
+
+?       Print options
+f       Fit data and graph fit with the current graph type (g,x,r,y,s)
+g       Graph the data and the current fit
+x,r     Graph the xi residuals versus x and y respectively
+y,s     Graph the eta residuals versus x and y respectively
+d,u     Delete or undelete the data point nearest the cursor
+o       Overplot the next graph
+c       Toggle the line of constant x and y plotting option
+t       Plot a line of constant x and y through nearest data point
+l       Print xishift, etashift, xscale, yscale, xrotate, yrotate
+q       Exit the interactive fitting code
+.fi
+
+The parameters listed below can be changed interactively with simple colon
+commands. Typing the parameter name along will list the current value.
+
+.nf
+:show                List parameters
+:projection          Sky projection 
+:refpoint            Sky projection reference point
+:fit      [value]    Fit type (shift,xyscale,rotate,rscale,rxyscale,general)
+:function [value]    Fitting function (chebyshev,legendre,polynomial)
+:xxorder  [value]    Xi fitting function order in x
+:xyorder  [value]    Xi fitting function order in y
+:yxorder  [value]    Eta fitting function order in x
+:yyorder  [value]    Eta fitting function order in y
+:xxterms  [n/h/f]    The xi fit cross terms type
+:yxterms  [n/h/f]    The eta fit cross terms type
+:maxiter  [value]    Maximum number of rejection iterations
+:reject   [value]    K-sigma rejection threshold
+.fi
+
+The final fit is stored in the text database file \fIdatabase\fR file in a
+format suitable for use by the CCSETWCS and CCTRAN tasks. Each fit is
+stored in a record whose name is the name of the input image \fIimage\fR
+if one is supplied, or the name of the input coordinate file \fIinput\fR.
+
+If the \fIupdate\fR switch is "yes" and an input image is specified,
+a new image wcs is derived from the linear component of the computed plate
+solution and written to the image header. The numerical components of
+the new image wcs are written to the standards FITS keywords, CRPIX, CRVAL,
+and CD, with the actual values depending on the input pixel coordinate
+system \fIpixsystem\fR. 
+The FITS keywords which define the image celestial coordinate
+system CTYPE, RADECSYS, EQUINOX, and MJD-WCS are set by the \fIinsystem\fR and
+\fIprojection\fR parameters. 
+
+The first four characters of the values of the ra / longitude and dec / latitude
+axis CTYPE keywords specify the celestial coordinate system. They are set to
+RA-- / DEC- for equatorial coordinate systems, ELON / ELAT for the ecliptic
+coordinate system, GLON / GLAT for the galactic coordinate system, and
+SLON / SLAT for the supergalactic coordinate system.
+
+The second four characters of the values of the ra / longitude and dec /
+latitude axis CTYPE keywords specify the sky projection geometry. IRAF
+currently supports the TAN, SIN, ARC, AIT, CAR, CSC, GLS, MER, MOL, PAR, PCO,
+QSC, STG, TSC, and ZEA standard projections, in which case the second 4
+characters of CTYPE are set to  -TAN, -ARC, -SIN, etc. IRAF and CCMAP also
+support the experiment TAN plus polynomials function driver. 
+
+If the input celestial coordinate system is equatorial, the value of the
+RADECSYS keyword specifies the fundamental equatorial system, EQUINOX
+specifies the epoch of the mean place, and MJD-WCS specifies the epoch 
+for which the mean place is correct. The permitted values of
+RADECSYS are FK4, FK4-NO-E, FK5, ICRS, and GAPPT. EQUINOX is entered in years
+and interpreted as a Besselian epoch for the FK4 system, a Julian epoch
+for the FK5 system. The epoch of the wcs MJD-WCS is entered as 
+a modified Julian date. Only those keywords necessary to defined the
+new wcs are written. Any existing keywords which are not required to
+define the wcs or are redundant are removed, with the exception of
+DATE-OBS and EPOCH, which are left unchanged for obvious (DATE_OBS) and
+historical (use of EPOCH keyword at NOAO) reasons.
+
+If \fIverbose\fR is "yes", various pieces of useful information are
+printed to the terminal as the task proceeds. If \fIresults\fR is set to a
+file name then the original pixel and celestial coordinates, the fitted
+celestial coordinates, and the residuals of the fit in arcseconds are written
+to that file.
+
+The transformation computed by the "general" fitting geometry is arbitrary
+and does not correspond to a physically meaningful model. However the computed
+coefficients for the linear term can be given a simple geometrical 
+interpretation for all the fitting geometries as shown below.
+
+.nf
+	fitting geometry = general (linear term)
+	     xi = a + b * x + c * y
+	    eta = d + e * x + f * y
+
+	fitting geometry = shift
+	     xi = a + x
+	    eta = d + y
+
+	fitting geometry = xyscale
+	     xi = a + b * x
+	    eta = d + f * y
+
+	fitting geometry = rotate
+	     xi = a + b * x + c * y
+	    eta = d + e * x + f * y
+	    b * f - c * e = +/-1
+	    b = f, c = -e or b = -f, c = e
+
+	fitting geometry = rscale
+	     xi = a + b * x + c * y
+	    eta = d + e * x + f * y
+	    b * f - c * e = +/- const
+	    b = f, c = -e or b = -f, c = e
+
+	fitting geometry = rxyscale
+	     xi = a + b * x + c * y
+	    eta = d + e * x + f * y
+	    b * f - c * e = +/- const
+.fi
+
+The coefficients can be interpreted as follows. X0, y0, xi0, eta0
+are the origins in the reference and input frames respectively. By definition
+xi0 and eta0 are 0.0 and 0.0 respectively. Rotation and skew are the rotation
+of the x and y axes and their deviation from perpendicularity respectively.
+Xmag and ymag are the scaling factors in x and y in " / pixel and are assumed
+to be positive by definition.
+
+.nf
+	general (linear term)
+	    xrotation = rotation - skew / 2
+	    yrotation = rotation + skew / 2
+	    b = xmag * cos (xrotation)
+	    c = ymag * sin (yrotation)
+	    e = -xmag * sin (xrotation)
+	    f = ymag * cos (yrotation)
+	    a = xi0 - b * x0 - c * y0 = xshift
+	    d = eta0 - e * x0 - f * y0 = yshift
+
+	shift
+	    xrotation = 0.0,  yrotation = 0.0
+	    xmag = ymag = 1.0
+	    b = 1.0
+	    c = 0.0
+	    e = 0.0
+	    f = 1.0
+	    a = xi0 - x0 = xshift
+	    d = eta0 - y0 = yshift
+
+	xyscale
+	    xrotation 0.0 / 180.0 yrotation = 0.0
+	    b = + /- xmag
+	    c = 0.0
+	    e = 0.0
+	    f = ymag
+	    a = xi0 - b * x0 = xshift
+	    d = eta0 - f * y0 = yshift
+
+	rscale
+	    xrotation = rotation + 0 / 180, yrotation = rotation
+	    mag = xmag = ymag
+	    const = mag * mag
+	    b = mag * cos (xrotation)
+	    c = mag * sin (yrotation)
+	    e = -mag * sin (xrotation)
+	    f = mag * cos (yrotation)
+	    a = xi0 - b * x0 - c * y0 = xshift
+	    d = eta0 - e * x0 - f * y0 = yshift
+
+	rxyscale
+	    xrotation = rotation + 0 / 180, yrotation = rotation
+	    const = xmag * ymag
+	    b = xmag * cos (xrotation)
+	    c = ymag * sin (yrotation)
+	    e = -xmag * sin (xrotation)
+	    f = ymag * cos (yrotation)
+	    a = xi0 - b * x0 - c * y0 = xshift
+	    d = eta0 - e * x0 - f * y0 = yshift
+.fi
+
+.ih
+REFERENCES
+
+
+Additional information on the IRAF world coordinate systems can be found in
+the help pages for the WCSEDIT and WCRESET tasks.
+Detailed documentation for the IRAF world coordinate system interface MWCS
+can be found in the file "iraf$sys/mwcs/MWCS.hlp". This file can be
+formatted and printed with the command "help iraf$sys/mwcs/MWCS.hlp fi+ |
+lprint".
+
+Details of the FITS header world coordinate system interface can
+be found in the draft paper "World Coordinate Systems Representations Within the
+FITS Format" by Hanisch and Wells, available from the iraf anonymous ftp
+archive and the draft paper which supersedes it "Representations of Celestial
+Coordinates in FITS" by Greisen and Calabretta available from the NRAO
+anonymous ftp archives.
+
+The spherical astronomy routines employed here are derived from the Starlink
+SLALIB library provided courtesy of Patrick Wallace. These routines
+are very well documented internally with extensive references provided
+where appropriate. Interested users are encouraged to examine the routines
+for this information. Type "help slalib" to get a listing of the SLALIB
+routines, "help slalib opt=sys" to get a concise summary of the library,
+and "help <routine>" to get a description of each routine's calling sequence,
+required input and output, etc. An overview of the library can be found in the
+paper "SLALIB - A Library of Subprograms", Starlink User Note 67.7
+by P.T. Wallace, available from the Starlink archives.
+
+
+
+.ih
+EXAMPLES
+
+1. Compute the plate scale for the test image dev$pix given the following
+coordinate list. Set the tangent point to the mean of the input celestial
+coordinates. Compute the plate scale interactively.
+
+.nf
+cl> type coords
+
+13:29:47.297  47:13:37.52  327.50  410.38
+13:29:37.406  47:09:09.18  465.50   62.10
+13:29:38.700  47:13:36.23  442.01  409.65
+13:29:55.424  47:10:05.15  224.35  131.20
+13:30:01.816  47:12:58.79  134.37  356.33
+
+cl> imcopy dev$pix pix
+
+cl> hedit pix epoch 1987.26 
+
+cl> ccmap coords coords.db image=pix xcol=3 ycol=4 lngcol=1 latcol=2
+
+    ... a plot of the mapping function appears
+    ... type ? to see the list of commands
+    ... type x to see the xi fit residuals versus x
+    ... type r to see the xi fit residuals versus y
+    ... type y to see the eta fit residuals versus x
+    ... type s to see the eta fit residuals versus y
+    ... type g to return to the default plot
+    ... type l to see the computed x and y scales in " / pixel
+    ... type q to quit and save fit
+.fi
+
+2. Repeat example 2 but compute the fit non-interactively and list the
+fitted values of the ra and dec and their residuals on the standard
+output.
+
+.nf
+cl> ccmap coords coords.db image=pix results=STDOUT xcol=3 ycol=4 \
+lngcol=1 latcol=2 inter- 
+
+# Coords File: coords  Image: pix
+#     Database: coords.db  Record: pix
+# Refsystem: j2000  Coordinates: equatorial FK5
+#     Equinox: J2000.000 Epoch: J2000.00000000 MJD: 51544.50000
+# Insystem: j2000  Coordinates: equatorial FK5
+#     Equinox: J2000.000 Epoch: J2000.00000000 MJD: 51544.50000
+# Coordinate mapping status
+#     XI fit ok.  ETA fit ok.
+#     Ra/Dec or Long/Lat fit rms: 0.229  0.241   (arcsec  arcsec)
+# Coordinate mapping parameters
+#     Sky projection geometry: tan
+#     Reference point: 13:29:48.129  47:11:53.37  (hours  degrees)
+#     Reference point: 318.735  273.900  (pixels  pixels)
+#     X and Y scale: 0.764  0.767  (arcsec/pixel  arcsec/pixel)
+#     X and Y axis rotation: 179.110  358.958  (degrees  degrees)
+# Wcs mapping status
+#     Ra/Dec or Long/Lat wcs rms: 0.229  0.241   (arcsec  arcsec)
+# 
+#                     Input Coordinate Listing
+# X      Y       Ra          Dec        Ra(fit)      Dec(fit)    Dra    Ddec
+# 
+327.5  410.4  13:29:47.30  47:13:37.5  13:29:47.28  47:13:37.9  0.128 -0.370
+465.5   62.1  13:29:37.41  47:09:09.2  13:29:37.42  47:09:09.2 -0.191 -0.062
+442.0  409.6  13:29:38.70  47:13:36.2  13:29:38.70  47:13:35.9  0.040  0.282
+224.3  131.2  13:29:55.42  47:10:05.2  13:29:55.40  47:10:05.1  0.289  0.059
+134.4  356.3  13:30:01.82  47:12:58.8  13:30:01.84  47:12:58.7 -0.267  0.091
+.fi
+
+3. Repeat the previous example but in this case input the position of the
+tangent point in fk4 1950.0 coordinates.
+
+.nf
+cl> ccmap coords coords.db image=pix results=STDOUT xcol=3 ycol=4 lngcol=1 \
+latcol=2 refpoint=user lngref=13:27:46.9 latref=47:27:16 refsystem=b1950.0 \
+inter- 
+
+# Coords File: coords  Image: pix
+#     Database: coords.db  Record: pix
+# Refsystem: b1950.0  Coordinates: equatorial FK4
+#     Equinox: B1950.000 Epoch: B1950.00000000 MJD: 33281.92346
+# Insystem: j2000  Coordinates: equatorial FK5
+#     Equinox: J2000.000 Epoch: J2000.00000000 MJD: 51544.50000
+# Coordinate mapping status
+#     XI fit ok.  ETA fit ok.
+#     Ra/Dec or Long/Lat fit rms: 0.229  0.241   (arcsec  arcsec)
+# Coordinate mapping parameters
+#     Sky projection geometry: tan
+#     Reference point: 13:29:53.273  47:11:48.36  (hours  degrees)
+#     Reference point: 250.256  266.309  (pixels  pixels)
+#     X and Y scale: 0.764  0.767  (arcsec/pixel  arcsec/pixel)
+#     X and Y axis rotation: 179.126  358.974  (degrees  degrees)
+# Wcs mapping status
+#     Ra/Dec or Long/Lat wcs rms: 0.229  0.241   (arcsec  arcsec)
+#
+#                     Input Coordinate Listing
+#  X      Y       Ra         Dec        Ra(fit)      Dec(fit)    Dra    Ddec
+
+327.5  410.4  13:29:47.30  47:13:37.5  13:29:47.28  47:13:37.9  0.128 -0.370
+465.5   62.1  13:29:37.41  47:09:09.2  13:29:37.42  47:09:09.2 -0.191 -0.062
+442.0  409.6  13:29:38.70  47:13:36.2  13:29:38.70  47:13:35.9  0.040  0.282
+224.3  131.2  13:29:55.42  47:10:05.2  13:29:55.40  47:10:05.1  0.289  0.059
+134.4  356.3  13:30:01.82  47:12:58.8  13:30:01.84  47:12:58.7 -0.267  0.091
+.fi
+
+Note the computed image scales are identical in examples 2 and 3 but that
+the assumed position of the tangent point is different (the second estimate
+is more accurate) producing different values for the pixel and celestial
+coordinates of the reference point and small differences in the computed
+rotation angles.
+ 
+4. Repeat the previous example but in this case extract the position of the
+tangent point in from the image header keywords RA, DEC, and EPOCH. 
+
+.nf
+cl> imheader pix l+ 
+
+...
+DATE-OBS= '05/04/87'            /  DATE DD/MM/YY
+RA      = '13:29:24.00'         /  RIGHT ASCENSION
+DEC     = '47:15:34.00'         /  DECLINATION
+EPOCH   =              1987.26  /  EPOCH OF RA AND DEC
+...
+
+cl> ccmap coords coords.db image=pix results=STDOUT xcol=3 ycol=4 \
+lngcol=1 latcol=2 refpoint=user lngref=RA latref=DEC refsystem=EPOCH \
+inter-
+
+# Coords File: coords  Image: pix
+#     Database: coords.db  Record: pix
+# Refsystem: fk4 b1987.26  Coordinates: equatorial FK4
+#     Equinox: B1987.260 Epoch: B1987.26000000 MJD: 46890.84779
+# Insystem: j2000  Coordinates: equatorial FK5
+#     Equinox: J2000.000 Epoch: J2000.00000000 MJD: 51544.50000
+# Coordinate mapping status
+#     XI fit ok.  ETA fit ok.
+#     Ra/Dec or Long/Lat fit rms: 0.229  0.241   (arcsec  arcsec)
+# Coordinate mapping parameters
+#     Sky projection geometry: tan
+#     Reference point: 13:29:56.232  47:11:38.19  (hours  degrees)
+#     Reference point: 211.035  252.447  (pixels  pixels)
+#     X and Y scale: 0.764  0.767  (arcsec/pixel  arcsec/pixel)
+#     X and Y axis rotation: 179.135  358.983  (degrees  degrees)
+# Wcs mapping status
+#     Ra/Dec or Long/Lat wcs rms: 0.229  0.241   (arcsec  arcsec)
+# 
+#                     Input Coordinate Listing
+#  X      Y       Ra         Dec        Ra(fit)      Dec(fit)    Dra    Ddec
+
+327.5  410.4  13:29:47.30  47:13:37.5  13:29:47.28  47:13:37.9  0.128 -0.370
+465.5   62.1  13:29:37.41  47:09:09.2  13:29:37.42  47:09:09.2 -0.191 -0.062
+442.0  409.6  13:29:38.70  47:13:36.2  13:29:38.70  47:13:35.9  0.040  0.282
+224.3  131.2  13:29:55.42  47:10:05.2  13:29:55.40  47:10:05.1  0.289  0.059
+134.4  356.3  13:30:01.82  47:12:58.8  13:30:01.84  47:12:58.7 -0.267  0.091
+
+.fi
+
+Note that the position of the tangent point is slightly different again but
+that this does not have much affect on the fitted coordinates for this image.
+
+5. Repeat the third example but this time store the computed world coordinate
+system in the image header and check the header update with the imheader and
+skyctran tasks.
+
+.nf
+cl> imheader pix l+ 
+...
+DATE-OBS= '05/04/87'            /  DATE DD/MM/YY
+RA      = '13:29:24.00'         /  RIGHT ASCENSION
+DEC     = '47:15:34.00'         /  DECLINATION
+EPOCH   =              1987.26  /  EPOCH OF RA AND DEC
+...
+
+cl> ccmap coords coords.db image=pix results=STDOUT xcol=3 ycol=4  \
+lngcol=1 latcol=2 refpoint=user lngref=13:27:46.9 latref=47:27:16    \
+refsystem=b1950.0 inter- update+
+
+# Coords File: coords  Image: pix
+#     Database: coords.db  Record: pix
+# Refsystem: b1950.0  Coordinates: equatorial FK4
+#     Equinox: B1950.000 Epoch: B1950.00000000 MJD: 33281.92346
+# Insystem: j2000  Coordinates: equatorial FK5
+#     Equinox: J2000.000 Epoch: J2000.00000000 MJD: 51544.50000
+# Coordinate mapping status
+# Coordinate mapping status
+#     XI fit ok.  ETA fit ok.
+#     Ra/Dec or Long/Lat fit rms: 0.229  0.241   (arcsec  arcsec)
+# Coordinate mapping parameters
+#     Sky projection geometry: tan
+#     Reference point: 13:29:53.273  47:11:48.36  (hours  degrees)
+#     Reference point: 250.256  266.309  (pixels  pixels)
+#     X and Y scale: 0.764  0.767  (arcsec/pixel  arcsec/pixel)
+#     X and Y axis rotation: 179.126  358.974  (degrees  degrees)
+# Wcs mapping status
+#     Ra/Dec or Long/Lat wcs rms: 0.229  0.241   (arcsec  arcsec)
+# Updating image header wcs
+# 
+# 
+#                     Input Coordinate Listing
+#  X      Y       Ra          Dec        Ra(fit)     Dec(fit)    Dra    Ddec
+
+327.5  410.4  13:29:47.30  47:13:37.5  13:29:47.28  47:13:37.9  0.128 -0.370
+465.5   62.1  13:29:37.41  47:09:09.2  13:29:37.42  47:09:09.2 -0.191 -0.062
+442.0  409.6  13:29:38.70  47:13:36.2  13:29:38.70  47:13:35.9  0.040  0.282
+224.3  131.2  13:29:55.42  47:10:05.2  13:29:55.40  47:10:05.1  0.289  0.059
+134.4  356.3  13:30:01.82  47:12:58.8  13:30:01.84  47:12:58.7 -0.267  0.091
+
+cl> imheader pix l+ 
+...
+DATE-OBS= '05/04/87'            /  DATE DD/MM/YY
+RA      = '13:29:24.00'         /  RIGHT ASCENSION
+DEC     = '47:15:34.00'         /  DECLINATION
+EPOCH   =              1987.26  /  EPOCH OF RA AND DEC
+...
+RADECSYS= 'FK5     '
+EQUINOX =                2000.
+MJD-WCS =              51544.5
+WCSDIM  =                    2
+CTYPE1  = 'RA---TAN'
+CTYPE2  = 'DEC--TAN'
+CRVAL1  =     202.471969550729
+CRVAL2  =     47.1967667056819
+CRPIX1  =     250.255619786203
+CRPIX2  =     266.308757328719
+CD1_1   =  -2.1224568721716E-4
+CD1_2   =  -3.8136850875221E-6
+CD2_1   =  -3.2384199624421E-6
+CD2_2   =  2.12935798198448E-4
+LTM1_1  =                   1.
+LTM2_2  =                   1.
+WAT0_001= 'system=image'
+WAT1_001= 'wtype=tan axtype=ra'
+WAT2_001= 'wtype=tan axtype=dec'
+...
+
+cl> skyctran coords STDOUT "pix log" "pix world" lngcol=3 latcol=4 trans+
+
+# Insystem: pix logical  Projection: TAN  Ra/Dec axes: 1/2
+#     Coordinates: equatorial FK5 Equinox: J2000.000
+#     Epoch: J2000.00000000 MJD: 51544.50000
+# Outsystem: pix world  Projection: TAN  Ra/Dec axes: 1/2
+#     Coordinates: equatorial FK5 Equinox: J2000.000
+#     Epoch: J2000.00000000 MJD: 51544.50000
+
+# Input file: incoords  Output file: STDOUT
+
+13:29:47.297  47:13:37.52 13:29:47.284 47:13:37.89
+13:29:37.406  47:09:09.18 13:29:37.425 47:09:09.24
+13:29:38.700  47:13:36.23 13:29:38.696 47:13:35.95
+13:29:55.424  47:10:05.15 13:29:55.396 47:10:05.09
+13:30:01.816  47:12:58.79 13:30:01.842 47:12:58.70
+
+.fi
+
+Note that two versions of the rms values are printed, one for the fit
+and one for the wcs fit. For the default fitting parameters these
+two estimates should be identical. If a non-linear high order plate
+solution is requested however, the image wcs will have lower precision
+than the than the full plate solution, because only the linear component
+of the plate solution is preserved in the wcs.
+
+.ih
+BUGS
+
+.ih
+SEE ALSO
+cctran,ccsetwcs,skyctran,imctran,finder.tfinder,finder.tastrom
+.endhelp
-- 
cgit 

