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author | Joe Hunkeler <jhunkeler@gmail.com> | 2015-08-11 16:51:37 -0400 |
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committer | Joe Hunkeler <jhunkeler@gmail.com> | 2015-08-11 16:51:37 -0400 |
commit | 40e5a5811c6ffce9b0974e93cdd927cbcf60c157 (patch) | |
tree | 4464880c571602d54f6ae114729bf62a89518057 /noao/digiphot/apphot/doc/datapars.hlp | |
download | iraf-osx-40e5a5811c6ffce9b0974e93cdd927cbcf60c157.tar.gz |
Repatch (from linux) of OSX IRAF
Diffstat (limited to 'noao/digiphot/apphot/doc/datapars.hlp')
-rw-r--r-- | noao/digiphot/apphot/doc/datapars.hlp | 290 |
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diff --git a/noao/digiphot/apphot/doc/datapars.hlp b/noao/digiphot/apphot/doc/datapars.hlp new file mode 100644 index 00000000..bacc5c77 --- /dev/null +++ b/noao/digiphot/apphot/doc/datapars.hlp @@ -0,0 +1,290 @@ +.help datapars May00 noao.digiphot.apphot +.ih +NAME +datapars -- edit the data dependent parameters +.ih +USAGE +datapars +.ih +PARAMETERS +.ls scale = 1.0 +The scale of the image in user units, e.g arcseconds per pixel. +All APPHOT distance dependent parameters are assumed to be in units of scale. +If scale = 1.0 these parameters are assumed to be in units of pixels. +Most APPHOT users should leave scale set to 1.0 unless they intend to +compare their aperture photometry results directly with data +in the literature. +.le +.ls fwhmpsf = 2.5 (scale units) +The full-width at half-maximum of the point spread function in scale units. +The DAOFIND, FITPSF and WPHOT tasks and the "gauss" and "ofilter" centering +algorithms depend on the value of fwhmpsf. APPHOT users can either determine +a value for fwhmpsf using an external task such as IMEXAMINE, or make use of +the interactive capabilities of the APPHOT tasks to set and store it. +.le +.ls emission = yes +The features to be measured are above sky. By default the APPHOT package +considers all features to be emission features. However all the package tasks +measure absorption features if emission is set to no. +.le +.ls sigma = INDEF +The standard deviation of the sky pixels. The DAOFIND task and the "constant" +sky fitting algorithm error estimate depend on the value of sigma. APPHOT +users should set sigma to a value which is representative of the noise +in the sky background. +.le +.ls datamin = INDEF +The minimum good pixel value. Datamin defaults to -MAX_REAL, the minimum +floating point number supported by the host computer. APPHOT users should +set this parameter if they wish to remove bad data from the sky pixel +distribution before the sky is fit or if they wish to flag stars with +bad data in the centering and / or photometry apertures. +.le +.ls datamax = INDEF +The maximum good pixel value. Datamax defaults to MAX_REAL the maximum +floating point number supported by the host computer. +APPHOT users should set this parameter if they wish to flag +saturated stars or stars with bad data in the centering and / or +photometry apertures. +.le +.ls noise = "poisson" +The noise model used to estimate the uncertainties in the computed APPHOT +magnitudes. The options are the following: +.ls poisson +Poisson statistics in the object and the sky background are used to estimate +the error in the object measurement. There are two components to the sky +noise measurement the sky noise in the object aperture and the mean error +in the estimated sky value. +.le +.ls constant +The standard deviation of the sky background is used to estimate the +error in the object measurement. There are two components to the error +estimate the sky noise in the object aperture and the mean error in the +estimated sky value. +.le + +Most APPHOT users should use the Poisson model appropriate for CCD detectors. +APPHOT users should also be aware that one or other of the parameters +gain or epadu must be set correctly in order to compute the magnitude +errors correctly. +.le +.ls ccdread = "" +The image header keyword defining the readout noise parameter whose units are +assumed to be electrons. +.le +.ls gain = "" +The image header keyword defining the gain parameter whose units are assumed +to be electrons per adu. +.le +.ls readnoise = 0.0 +The readout noise of the image in electrons. APPHOT users should set this +parameter or the ccdread parameter to its correct value before running any +of the APPHOT tasks. +.le +.ls epadu = 1.0 +The gain in electrons per adu. APPHOT users should set epadu or ain to its +correct value before running any of the APPHOT tasks in order to insure that +the magnitude error estimates are correct. +.le +.ls exposure = "" +The image header exposure time keyword. The time units are arbitrary but +must be consistent for any list of images whose magnitudes are to be compared. +The computed magnitudes are normalized to 1 timeunit. Setting the exposure +parameter will greatly simplify future reduction steps. The value of exposure +is recorded in the APPHOT output file. +.le +.ls airmass = "" +The image header airmass keyword. The airmass parameter is not used +directly by APPHOT but the airmass value is stored in the output file +and its presence there will simplify future calibration steps. +.le +.ls filter = "" +The image header filter id keyword. The filter parameter is not used +directly by APPHOT but the filter id is stored in the output file +and its presence there will simplify future calibration steps. +.le +.ls obstime = "" +The image header time of observation keyword. The obstime parameter is not used +directly by APPHOT but the obstime value is stored in the output file +and its presence there will simplify future calibration steps. +.le +.ls itime = 1.0 +The exposure time for the image in arbitrary units. The APPHOT magnitudes are +normalized to 1 timeunit using the value of exposure in the image header +if exposure is defined or the value of itime. +.le +.ls xairmass = INDEF +The airmass value. The airmass is read from the image header if airmass +is defined or from xairmass. The airmass value is stored in the APPHOT +output files. +.le +.ls ifilter = "INDEF" +The filter id string. The filter id is read from the image header if filter +is defined otherwise from ifilter. The filter id is stored in the APPHOT +output files. +.le +.ls otime = "INDEF" +The value of the time of observation. The time of observation is read from +the image header if obstime is defined otherwise from otime. The time of +observation is stored in the APPHOT output files. +.le +.ih +DESCRIPTION +\fIDatapars\fR sets the image data dependent parameters. These parameters are +functions, of the instrument optics, the noise characteristics and range of +linearity of the detector, and the observing conditions. Many of the +centering, sky fitting, and photometry algorithm parameters in the CENTERPARS, +FITSKYPARS and PHOTPARS parameter sets scale with the data dependent +parameters. + +The parameter \fIscale\fR sets the scale of the apertures used by the +centering, sky fitting and photometry algorithms. Scale converts radial +distance measurements in pixel units to radial distance measurements in +scale units. The APPHOT parameters, cbox, maxshift, rclean and rclip +in the CENTERPARS parameter set; annulus, dannulus, and rgrow in +the FITSKYPARS parameter set; and apertures in the PHOTPARS +parameter set are expressed in units of the scale. The scale parameter is +useful in cases where the observations are to be compared to published +aperture photometry measurements in the literature. + +The parameter \fIfwhmpsf\fR defines the full-width at half-maximum of the +stellar point spread function. Most APPHOT tasks and algorithms do not +require this parameter. The exceptions are the DAOFIND task, the centering +algorithms "gauss" and "ofilter", the FITPSF task, and the WPHOT task. + +By setting the \fIscale\fR and \fIfwhmpsf\fR appropriately the aperture +sizes and radial distances may be expressed in terms of the half-width +at half-maximum of the stellar point spread function. The way to do this +is to define the scale parameter in units of the number of half-width at +half-maximum per pixel, set the fwhmpsf parameter to 2.0, and then +set the remaining scale dependent centering, sky fitting and photometry +algorithm parameters in CENTERPARS, FITSKYPARS and PHOTPARS to +appropriate values in units of the half-width at half-maximum of the +point-spread function. Once an optimum set of algorithm parameters is +chosen, the user need only alter the DATAPARS scale parameter before +executing an APPHOT task on a new image. + +If \fIemission\fR is "yes", the features to be measured are assumed to be +above sky. By default the APPHOT package considers all measurements to +be measurements of emission features. In most cases APPHOT users should +leave emission set to "yes". + +The parameter \fIsigma\fR estimates the standard deviation of the sky +background pixels. The star finding algorithm in DAOFIND uses sigma +and the \fIfindpars.threshold\fR parameter to define the stellar +detection threshold in adu. The centering algorithms uses sigma, +1) with the \fIcenterpars.kclean\fR parameter to define deviant pixels +if \fIcenterpars.clean\fR is enabled; 2) to estimate the signal to +noise ratio in the centering box; 3) and with the \fIcenterpars.cthreshold\fR +parameter to define the lower intensity limit for the pixels to be used +for centering. If sigma is undefined or <= 0.0 1) no cleaning is performed +regardless of the value of centerpars.clean; 2) the background +noise in the centering box is assumed to be 0; and 3) default cutoff +intensity intensity is used for centering. + +The \fIdatamin\fR and \fIdatamax\fR parameters define the good data range. +If datamin or datamax are defined bad data is removed from the sky pixel +distribution before the sky is fit, data containing bad pixels in the +photometry apertures is flagged, and the corresponding aperture photometry +magnitudes are set to INDEF. APPHOT users should set datamin and datamax +to appropriate values before running the APPHOT tasks. + +Two noise models are available "constant" and "poisson". If \fInoise\fR = +constant, the total noise is assumed to be due to noise in the sky background +alone. If \fInoise\fR = poisson, the total noise includes Poisson noise from +the object and the sky noise. + +The parameters \fIgain\fR and \fIepadu\fR define the image gain. +The gain parameter specifies which keyword in the image header contains +the gain value. If gain is undefined or not present in the image header +the value of epadu is used. Epadu must be in units of electrons per adu. +APPHOT users should set either gain or epadu before running any +APPHOT tasks to insure the magnitude error computations are correct. + +The two parameters \fIccdread\fR and \fIreadnoise\fR define the image +readout noise. The ccdread parameter specifies which keyword in the +image header contains the readout noise value. If ccdread is undefined or +not present in the image header the value of readnoise is used. +Readnoise is assumed to be in units of electrons. +APPHOT users should set either ccdread or readnoise before running any +APPHOT tasks to insure the magnitude error computations are correct. + +The magnitudes are normalized to an exposure time of 1 timeunit using +the value of the exposure time in the image header parameter \fIexposure\fR +or \fIitime\fR. If exposure is undefined or not present in the image header +the value of itime is used. Itime can be in arbitrary units. +Setting either exposure or itime will simplify future analysis steps. + +The parameters \fIairmass\fR and \fIxairmass\fR define the airmass +of the observation. The airmass parameter specifies which keyword in the +image header contains the airmass value. If airmass is undefined or +not present in the image header the value of xairmass is used. +The airmass values are not used in any APPHOT computations, however their +presence in the APPHOT output files will simplify future reduction steps. + +The parameters \fIfilter\fR and \fIifilter\fR define the filter +of the observation. The filter parameter specifies which keyword in the +image header contains the filter id. If filter is undefined or not present +in the image header the value of ifilter is used. The filter id values are +not used in any APPHOT computations, however their presence in the APPHOT +output files can will simplify future reduction steps. + +The parameters \fIobstime\fR and \fIotime\fR define the time +of the observation (e.g. UT). The obstime parameter specifies which keyword +in the image header contains the time stamp of the observation. If obstime is +undefined or not present in the image header the value of otime is used. +The time of observations values are not used in any APPHOT +computations, however their presence in the APPHOT output files can +greatly simplify future reduction steps. + +.ih +EXAMPLES + +1. List the data dependent parameters. + +.nf + ap> lpar datapars +.fi + +2. Edit the data dependent parameters. + +.nf + ap> datapars +.fi + +3. Edit the DATAPARS parameters from within the PHOT task. + +.nf + da> epar phot + + ... edit a few parameters + + ... move to the datapars parameter and type :e + + ... edit the datapars parameters and type :wq + + ... finish editing the phot parameters and type :wq +.fi + +4. Save the current DATAPARS parameter set in a text file datnite1.par. +This can also be done from inside a higher level task as in the +previous example. + +.nf + da> datapars + + ... edit a few parameters + + ... type ":w datnite1.par" from within epar +.fi + +.ih +TIME REQUIREMENTS + +.ih +BUGS + +.ih +SEE ALSO +epar,lpar,daofind,center,fitsky,phot,wphot,polyphot,radprof,fitpsf +.endhelp |