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diff --git a/noao/digiphot/daophot/doc/fitskypars.hlp b/noao/digiphot/daophot/doc/fitskypars.hlp new file mode 100644 index 00000000..6642a551 --- /dev/null +++ b/noao/digiphot/daophot/doc/fitskypars.hlp @@ -0,0 +1,212 @@ +.help fitskypars May00 noao.digiphot.daophot +.ih +NAME +fitskypars - edit the sky fitting algorithm parameters +.ih +USAGE +fitskypars +.ih +PARAMETERS +.ls salgorithm = "mode" +The sky fitting algorithm. The sky fitting options are: +.ls constant +Use a user supplied constant sky value. +This algorithm is useful for measuring large resolved objects on flat +backgrounds such as galaxies or comets. +.le +.ls file +Read sky values from a text file. This option is useful for importing +user determined sky values into DAOPHOT. +.le +.ls mean +Compute the mean of the sky pixel distribution. This algorithm is useful +for computing sky values in regions with few background counts. +.le +.ls median +Compute the median of the sky pixel distribution. This algorithm is a useful +for computing sky values in regions with rapidly varying sky backgrounds +and is a good alternative to "centroid". +.le +.ls mode +Compute the mode of the sky pixel distribution using the mean and median. +This is the recommended algorithm for DAOPHOT users measuring stellar objects in +crowded stellar fields. Mode may not perform well in regions with +rapidly varying sky backgrounds. +.le +.ls centroid +Compute the intensity weighted mean of the sky pixel histogram. This algorithm +is reasonably robust in regions with rapidly varying or crowded sky backgrounds +and is a good alternative to "median". +.le +.ls gauss +Fit a Gaussian function to the sky pixel histogram using non-linear least- +squares techniques to determine the peak. +.le +.ls ofilter +Optimally filter the sky pixel histogram using a triangular weighting +function to determine the peak. +.le +.ls crosscor +Compute the peak of the cross-correlation function of the pixel distribution +and a Gaussian noise function to determine the peak. +.le +.ls histplot +Mark the peak of the sky pixel histogram with the graphics cursor. +This algorithm is useful for making careful interactive sky measurements +for a small number of objects in complicated regions or for checking the +behavior of other sky algorithms. +.le +.ls radplot +Mark the sky level on a radial profile plot with the graphics cursor. +This algorithm is useful for making careful interactive sky measurements +for a small number of objects in complicated regions or for checking the +behavior of other sky algorithms. +.le +.le +.ls annulus = 10.0 (scale units) +The inner radius of the annular sky fitting region in units of the DATAPARS +scale parameter. +.le +.ls dannulus = 10.0 (scale units) +The width of the annular sky fitting region in units of the DATAPARS scale +parameter. +.le +.ls skyvalue = 0.0 +The constant for constant sky subtraction. +.le +.ls smaxiter = 10 +The maximum number of iterations performed by the sky fitting algorithm. +Smaxiter is required by the "gauss" and "ofilter" sky fitting algorithms. +.le +.ls sloclip = 0.0, shiclip = 0.0 (percent) +The high and low side clipping parameters in percent of the total number +of pixels. If either of these parameters > 0.0 then the specified +percentage of the pixels will be removed from the sky pixel distribution +before any sky fitting is done. +.le +.ls snreject = 50 +The maximum number of sky pixel rejection cycles. +.le +.ls sloreject = 3.0, shireject = 3.0 +The k-sigma clipping factors for the pixel rejection phase of the +sky fitting algorithm. Sloreject and shireject are in units of the +computed sky sigma. +.le +.ls khist = 3.0 +The k-sigma clipping factor for computing the sky pixels histogram. Khist is in +units of sigma of the local sky pixel distribution. The histogram will be +2.0 * khist * sigma wide. Khist is used by the "centroid", "gauss", +"crosscor", "ofilter", and "histplot" sky fitting algorithms. +.le +.ls binsize = 0.10 +The width of a single bin of the sky pixel histogram. Binsize is in units of +the sigma of the local sky pixel distribution. Binsize is used by the +"centroid", "gauss", "crosscor", "ofilter", and "histplot" sky fitting +algorithms. +.le +.ls smooth = no +Boxcar smooth the sky pixel histogram before computing a sky value. +Smooth is used by the "centroid", "gauss", "crosscor", "ofilter", and +"histplot" sky fitting algorithms. +.le +.ls rgrow = 0.0 (scale units) +The region growing radius for pixel rejection in the sky region in units +of the DATAPARS scale parameter. When a bad sky_pixel is detected, all pixels +within rgrow / scale pixels of the bad pixel will be rejected. If rgrow is +0.0 region growing is disabled. +.le +.ls mksky = no +Mark the sky annuli on the displayed image ? +.le +.ih +DESCRIPTION +The sky fitting algorithm parameters control the action of the sky fitting +algorithms. The default parameter settings should give reasonable results in +the majority of cases. Several of the sky fitting parameters scale with +image scale, \fIscale\fR which is data dependent. +\fIScale\fR is defined in the DATAPARS parameter set. + +Sky pixels in an annular region of inner radius \fIannulus / scale\fR pixels +and a width of \fIdannulus / scale\fR pixels are extracted from the IRAF image. +If the \fIscale\fR parameter is defined in terms of the number of half-width +at half-maximum of the point spread function per pixel, then single values of +annulus and dannulus will work well for images with different seeing and +detector characteristics. + +Pixels outside of the good data range specified by \fIdatamin\fR and +\fIdatamax\fR are rejected from the sky pixel distribution. After bad +data rejection \fIPloclip\fR and \fIphiclip\fR percent pixels are rejected +from the low and high sides of the sorted pixel distribution before any +sky fitting is done. + +Sky values are computed using the sky fitting algorithm specified by +\fIsalgorithm\fR. The default value is "centroid". If \fIsalgorithm\fR += "mean", "median" or "mode", the sky value is computed directly from the +array of sky pixels. The remaining sky fitting algorithms use the histogram +of the object sky pixels. The computed histogram is \fIkhist\fR * sigma wide +with a bin width of \fIbinsize\fR * sigma where sigma is the computed +standard deviation of the sky pixels for each object. If \fIsmooth\fR = yes, +boxcar smoothing is performed on the computed histogram before sky fitting. +The mode of the histogram is computed using, a non-linear least squares +fit to a Gaussian (salgorithm = "gauss"), optimal filtering of the histogram +(salgorithm = "ofilter"), computing the centroid of the histogram +(salgorithm = "centroid"), or by cross-correlation techniques +(salgorithm = "crosscor"). + +Two interactive methods of fitting sky are also available. If \fIsalgorithm\fR +is "radplot" or "histplot", the user must interactively set +the value of the sky using a radial profile or a histogram plot. + +Pixels which deviate from the sky value by more than \fIkreject times the +computed sky sigma are rejected from the fit. If \fIrgrow\fR > 0, pixels +within a radius of rgrow / scale of the rejected pixel are also rejected from +the fit. The rejection procedure iterates until no further pixels are rejected, +all pixels are rejected, or the maximum number of rejection cycles +\fIsnreject\fR iterations is reached. + +.ih +EXAMPLES + +1. List the sky fitting parameters. + +.nf + da> lpar fitskypars +.fi + +2. Edit the sky fitting parameters. + +.nf + da> fitskypars +.fi + +3. Edit the FITSKYPARS parameters from with the PHOT task. + +.nf + da> epar phot + + ... edit a few phot parameters + + ... move to the fitskypars parameter and type :e + + ... edit the fitskypars parameters and type :wq + + ... finish editing the phot parameters and type :wq +.fi + +4. Save the current FITSKYPARS parameter set in a text file skynite1.par. +This can also be done from inside a higher level task as in the +above example. + +.nf + da> epar fitskypars + + ... type ":w skynite1.par" from within epar +.fi +.ih +TIME REQUIREMENTS +.ih +BUGS +.ih +SEE ALSO +epar,lpar,datapars,phot +.endhelp |