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diff --git a/noao/twodspec/longslit/doc/response.hlp b/noao/twodspec/longslit/doc/response.hlp new file mode 100644 index 00000000..61a7b34a --- /dev/null +++ b/noao/twodspec/longslit/doc/response.hlp @@ -0,0 +1,178 @@ +.help response Aug86 noao.twodspec.longslit +.ih +NAME +response -- Determine response calibrations +.ih +USAGE +response calibration normalization response +.ih +PARAMETERS +.ls calibration +Images to use in determining response calibrations. These are +generally quartz continuum spectra. An image section may be used to select +only a portion of the image. +.le +.ls normalization +Images to use determining the normalization spectrum. In almost all cases +the normalization images are the same as the calibration images or a +subsection of the calibration images. +.le +.ls responses +Response calibration images to be created. Each response 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 calibration spectrum and fit the normalization spectrum +interactively? +.le +.ls threshold = INDEF +Set the response to 1 when the normalization spectrum or input image data +fall below this value. If INDEF then no threshold is applied. +.le +.ls sample = "*" +Sample of points to use in fitting the average calibration spectrum. +The sample is selected with a range string. +.le +.ls naverage = 1 +Number of sample points to average or median before fitting the 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 normalization spectrum. +.le +.ls function = "spline3" +Function to fit to the average image spectrum to form the normalization +spectrum. 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 +.ih +CURSOR KEYS +The interactive curve fitting package \fBicfit\fR is used to fit a function +to the average calibration spectrum. Help for this package is found +under the name "icfit". +.ih +DESCRIPTION +A response calibration, in the form of an image, is created for each input +image, normally a quartz spectrum. The response calibration is formed by +dividing the calibration image by a normalization spectrum which is the +same at all points along the spatial axis. The normalization spectrum is +obtained by averaging the normalization image across the dispersion to form +a one dimensional spectrum and smoothing the spectrum by fitting a +function. The threshold value does not apply to creating or fitting of +the normalization spectrum but only the final creation of the response +values. When normalizing (that is dividing the data values by the +fit to the normalization spectrum) only pixels in which both the fitted +normalization value and the data value are above the threshold are +computed. If either the normalization value or the data value is below +the threshold the output response value is one. + +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 response +everywhere. Subsequently the response is only modified in those regions +occupied by the input calibration image. Thus, image sections may be used +to select regions in which the response is desired. This ability is +particularly useful when dealing with multiple slits within an image or to +exclude regions outside the slit. + +Normally the normalization images are the same as the calibration images. +In other words the calibration image is normalized by the average spectrum +of the calibration image itself. Sometimes, however, the normalization +image may be a smaller image section of the calibration image to avoid +contaminating the normalization spectrum by effects at the edge of the +slit. Again, this may be quite useful in multi-slit images. + +The normalization spectrum is smoothed by fitting a function +using the interactive curve fitting package (\fBicfit\fR). The +parameters determining the fitted normalization spectrum 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 spectrum are +selected by a range string. Points in the normalization spectrum 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 function may be examined and modified interactively when the +parameter \fIinteractive\fR is set. In this case the normalization spectrum +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 a carriage +return or 'q' and the calibration image will be created. Changes in +the fitted parameters are remembered from image to image within the +task but not outside the task. + +When the task finishes creating a response image the fitting parameters +are updated in the parameter file. +.ih +EXAMPLES +1. To create a response image non-interactively: + + cl> response quartz quartz response order=20 interactive=no + +2. To determine independent responses for a multislit image determine the +image sections defining each slit. Then the responses are computed as +follows: + +.nf + cl> response quartz[10:20,*],quartz[35:45,*] \ + >>> quartz[12:18,*],quartz[12:18,*] resp,resp +.fi + +Generally the slit image sections are prepared in a file which is then +used to define the lists of input images and response. + +.nf + cl> response @slits @slits @responses +.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, iillumination +.endhelp |