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diff --git a/noao/twodspec/longslit/doc/illumination.hlp b/noao/twodspec/longslit/doc/illumination.hlp new file mode 100644 index 00000000..5697bfad --- /dev/null +++ b/noao/twodspec/longslit/doc/illumination.hlp @@ -0,0 +1,220 @@ +.help iillumination Jul86 noao.twodspec.longslit +.ih +NAME +iillumination -- Determine iillumination calibrations +.ih +USAGE +iillumination images iilluminations +.ih +PARAMETERS +.ls images +Images to use in determining iillumination calibrations. These are +generally sky spectra. An image section may be used to select only a +portion of the image. +.le +.ls iilluminations +Iillumination calibration images to be created. Each iillumination image is +paired with a calibration image. If the image exists then it will be modified +otherwise it is created. +.le +.ls interactive = yes +Graph the average spectrum and select the dispersion bins +and graph and fit the slit profile for each dispersion bin interactively? +.le +.ls bins = "" +Range string defining the dispersions bins within which the slit profiles +are determined. If the range string is null then the dispersion +bins are determined by the parameter \fInbins\fR. +.le +.ls nbins = 5 +If the dispersion bins are not specified explicitly by the parameter +\fIbins\fR then the dispersion range is divided into this number of +nearly equal bins. +.le +.ls sample = "*" +Sample of points to use in fitting each slit profile. +The sample is selected with a range string. +.le +.ls naverage = 1 +Number of sample points to average or median before fitting a function. +If the number is positive the average of each set of naverage sample +points is formed while if the number is negative then the median of each set +of points (in absolute value) is formed. This subsample of points is +used in fitting the slit profile. +.le +.ls function = "spline3" +Function to fit to each dispersion bin to form the iillumination function. +The options are "spline1", "spline3", "legendre", and "chebyshev". +.le +.ls order = 1 +Order of the fitting function or the number of spline pieces. +.le +.ls low_reject = 0., high_reject = 0. +Rejection limits below and above the fit in units of the residual sigma. +.le +.ls niterate = 1 +Number of rejection iterations. +.le +.ls grow = 0 +Reject additional points within this distance of points exceeding the +rejection threshold. +.le +.ls interpolator = "poly3" +Interpolation type. One of "nearest", "linear", "poly3", "poly5", or +"spline3". +.le +.ls graphics = "stdgraph" +Graphics output device. May be one of the standard devices "stdgraph", +"stdplot", or "stdvdm" or an explicit device. +.le +.ls cursor = "" +Graphics input device. May be either null for the standard graphics cursor +or a file containing cursor commands. +.le +.ih +CURSOR KEYS +The interactive curve fitting package \fBicfit\fR is used to fit a function +to the average calibration spectrum. Additional help on using this package +and the cursor keys is available under the name "icfit". + +When the dispersion bins are set graphically the following cursor keys are +defined. + +.ls ? +Clear the screen and print a menu of the cursor options. +.le +.ls i +Initialize the sample ranges. +.le +.ls q +Exit interactive dispersion bin selection. +.le +.ls s +Set a bin with the cursor. This may be repeated any number of times. +Two keystrokes are required to mark the two ends of the bin. +.le + +The parameters are listed or set with the following commands which may be +abbreviated. To list the value of a parameter type the command alone. + +.nf +:bins value Iillumination bins +:show Show the values of all the parameters +.fi +.ih +DESCRIPTION +An iillumination calibration, in the form of an image, is created for each +longslit calibration image, normally a sky spectrum. The iillumination +calibration is determined by fitting functions across the slit (the slit +profiles) at a number of points along the dispersion, normalizing each fitted +function to unity at the center of the slit, and interpolating the iillumination +between the dispersion points. The fitted data is formed by dividing the +dispersion points into a set of bins and averaging the slit profiles within +each bin. The interpolation type is a user parameter. + +The image header keyword DISPAXIS must be present with a value of 1 for +dispersion parallel to the lines (varying with the column coordinate) or 2 +for dispersion parallel to the columns (varying with line coordinate). +This parameter may be added using \fBhedit\fR. Note that if the image has +been transposed (\fBimtranspose\fR) the dispersion axis should still refer +to the original dispersion axis unless the physical world coordinate system +is first reset (see \fBwcsreset\fR). This is done in order to allow images +which have DISPAXIS defined prior to transposing to still work correctly +without requiring this keyword to be changed. + +If the output image does not exist it is first created with unit iillumination +everywhere. Subsequently the iillumination is only modified in those regions +occupied by the input image. Thus, an image section in the input image may +be used to select the data to be used and for which an iillumination calibration +will be determined. This ability is particularly userful when dealing with +multiple slits or to exclude regions outside the slit. + +The dispersion bins may be selected by a range string (\fIbins\fR) or, +if no range string is given, by the number of bins into which the dispersion +range is to be divided (\fInbins\fR). When the interactive parameter +is set (\fIinteractive\fR) then the average spectrum is graphed and the +bins may be set using the cursor or with a colon command. Once the bins +have been selected exit with (q)uit to continue to the slit profile fitting. + +Fitting of the slit profiles is done using the interactive curve fitting +package (\fBicfit\fR). The parameters determining the fit are the +sample points, the averaging bin size, the fitting function, +the order of the function, the rejection sigmas, the number of +rejection iterations, and the rejection width. +The sample points for the average slit profile are selected by a range string. +Points in the slit profile not in the sample are not used in determining +the fitted function. The selected sample points may be binned into a +set of averages or medians which are used in the function fit instead of the +sample points with the averaging bin size parameter +\fInaverage\fR. This parameter selects the number of sample points to be +averaged if its value is positive or the number of points to be medianed +if its value is negative (naturally, the absolute value is used for the +number of points). A value of one uses all sample points without binning. +The fitted function may be used to reject points from the fit using the +parameters \fIlow_reject, high_reject, niterate\fR and \fIgrow\fR. If +one or both of the rejection limits are greater than zero then the sigma +of the residuals is computed and points with residuals less than +\fI-low_reject\fR times the sigma and greater than \fIhigh_reject\fR times +the sigma are removed and the function fitted again. In addition points +within a distance given by the parameter \fIgrow\fR of the a rejected point +are also rejected. A value of zero for this parameter rejects only the +points exceeding the rejection threshold. Finally, the rejection procedure +may be iterated the number of times given by the parameter \fIniterate\fR. + +The fitted functions may be examined and modified interactively when the +parameter \fIinteractive\fR is set. The user is asked before each dispersion +bin whether to perform the fit interactively. The possible response are +"no", "yes", "NO", and "YES". The lower case responses only affect the +specified dispersion bin while the upper case responses affect all following +dispersion bins for the current image. Thus, if the response is "NO" then +no further prompts or interactive curve fitting need be performed while if +the response is "YES" there are no further prompts but the slit profile +for each dispersion bin must be graphed and exited with (q)uit. +Changes to the fitting parameters remain in effect until they are next +changed. This allows the fitting parameters to be selected from only the first +dispersion bin without requiring each dispersion bin to be graphed and +confirmed. + +When a dispersion bin is to be fitted interactively the average slit profile +and the fitted function or the residuals of the fit are graphed. +Deleted points are marked with an x and rejected points by a diamond. +The sample regions are indicated along the bottom of the graph. +The cursor keys and colon commands are used to change the values +of the fitting parameters, delete points, and window and expand the +graph. When the fitted function is satisfactory exit with +with a carriage return or 'q'. The prompt for the next dispersion bin will +then be given until the last dispersion bin has been fit. The iillumination +calibration image is then created. +.ih +EXAMPLES +1. To create an iillumination image non-interactively: + +.nf + cl> iillumination sky illum nbins=8 order=20 interactive=no +.fi + +2. To determine independent iilluminations for a multislit image determine the +image sections defining each slit. Then the iillumination functions are +computed as follows: + +.nf + cl> iillumination sky[10:20,*],sky[35:45,*] illum,illum +.fi + +3. Generally the slit image sections are prepared in a file which is then +used to define the lists of input images and iilluminations. + +.nf + cl> iillumination @slits @illums +.fi + +3. If the DISPAXIS keyword is missing and the dispersion is running +vertically (varying with the image lines): + +.nf + cl> hedit *.imh dispaxis 2 add+ +.fi +.ih +SEE ALSO +icfit, response +.endhelp |