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diff --git a/noao/digiphot/apphot/doc/fitskypars.hlp b/noao/digiphot/apphot/doc/fitskypars.hlp new file mode 100644 index 00000000..cdb541ba --- /dev/null +++ b/noao/digiphot/apphot/doc/fitskypars.hlp @@ -0,0 +1,219 @@ +.help fitskypars May00 noao.digiphot.apphot +.ih +NAME +fitskypars - edit the sky fitting algorithm parameters +.ih +USAGE +fitskypars +.ih +PARAMETERS +.ls salgorithm = "centroid" +The sky fitting algorithm to be employed. The sky fitting options are: +.ls constant +Use a user supplied constant value \fIskyvalue\fR for the sky. +This algorithm is useful for measuring large resolved objects on flat +backgrounds such as galaxies or comments. +.le +.ls file +Read sky values from a text file. This option is useful for importing +user determined sky values into APPHOT. +.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 computed mean and +median. This is the recommended algorithm for APPHOT users trying to +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 or centroid of the sky pixel histogram. +This is the algorithm recommended for most APPHOT users. It is reasonably +robust in rapidly varying and crowded regions. +.le +.ls gauss +Fit a single Gaussian function to the sky pixel histogram using non-linear +least-squares techniques. +.le +.ls ofilter +Compute the sky using the optimal filtering algorithm and a triangular +weighting function and the histogram of the sky pixels. +.le +.ls crosscor +Compute the sky value using the cross-correlation function of the sky pixel +histogram and a Gaussian noise function with a sigma equal to the +computed sigma of the sky pixel distribution. +.le +.ls histplot +Mark the peak of the histogram of the sky pixels on a plot of the histogram. +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 value on a radial distribution plot of the sky pixels. +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 +The constant for constant sky subtraction. +.le +.ls smaxiter = 10 +The maximum number of iterations performed by the sky fitting algorithm. +\fISmaxiter\fR is required by the "gauss" and "ofilter" sky fitting algorithms. +.le +.ls sloclip = 0.0 (percent) +The low-side clipping factor in percentage points of the total number of +sky pixels. +.le +.ls shiclip = 0.0 (percent) +The high-side clipping factor in percentage points of the total number of +sky pixels. +.le +.ls snreject = 50 +The maximum number of pixel rejection cycles. +.le +.ls sloject = 3.0 +The ksigma low-side clipping factor for the pixel rejection phase of the +sky fitting algorithm. \fIsloreject\fR is in units of the computed sky +sigma. +.le +.ls shiject = 3.0 +The ksigma high-side clipping factor for the pixel rejection phase of the +sky fitting algorithm. \fIshireject\fR is in units of the computed sky +sigma. +.le +.ls khist = 3.0 +The ksigma clipping factor for computing the histogram of the sky pixels. +\fIKhist\fR is in units of the computed sky sigma. +The computed histogram will be 2.0 * khist * sigma wide. +.le +.ls binsize = 0.10 +The width of a single bin of the histogram of sky values. +\fIBinsize\fR is in units of the computed sky sigma. +.le +.ls smooth = no +Boxcar smooth the histogram before computing a sky value ? +.le +.ls rgrow = 0.0 (scale units) +The region growing radius for pixel rejection in the sky region, in units +of the DATAPARS \fIscale\fR parameter. When a bad sky pixel is detected, +all pixels within rgrow / scale will be rejected. If rgrow is 0.0 +region growing is not performed. +.le +.ls mksky = no +Mark the sky annulus 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 intensity weighted mean 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 profile plot. + +Pixels which deviate from the sky value by more than \fIkreject\fR 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 + ap> lpar fitskypars +.fi + +2. Edit the sky fitting parameters. + +.nf + ap> fitskypars +.fi + +3. Edit the FITSKYPARS parameters from within 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> fitskypars + + ... edit some parameters + + ... type ":w skynite1.par" from within epar +.fi + +.ih +TIME REQUIREMENTS + +.ih +BUGS + +.ih +SEE ALSO +radprof,fitsky,phot,wphot,polyphot +.endhelp |