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diff --git a/noao/digiphot/apphot/doc/findpars.hlp b/noao/digiphot/apphot/doc/findpars.hlp new file mode 100644 index 00000000..22fa7668 --- /dev/null +++ b/noao/digiphot/apphot/doc/findpars.hlp @@ -0,0 +1,134 @@ +.help findpars May00 noao.digiphot.apphot +.ih +NAME +findpars -- edit the star detection parameters +.ih +USAGE +findpars +.ih +PARAMETERS +.ls threshold = 4.0 (sigma) +The object detection threshold above local background in units of +\fIdatapars.sigma\fR. +.le +.ls nsigma = 1.5 +The semi-major axis of the Gaussian convolution kernel used to computed the +density enhancement and mean density images in Gaussian sigma. This semi- +major axis is equal to min (2.0, 0.42466 * \fInsigma\fR * +\fIdatapars.fwhmpsf\fR / \fIdatapars.scale\fR) pixels. +.le +.ls ratio = 1.0 +The ratio of the sigma of the Gaussian convolution kernel along the minor axis +direction to the sigma along the major axis direction. \fIRatio\fR defaults +to 1.0 in which case the image is convolved with a circular Gaussian. +.le +.ls theta = 0.0 +The position angle of the major axis of the Gaussian convolution kernel. +\fITheta\fR is measured in degrees counter-clockwise from the x axis. +.le +.ls sharplo = .2, sharphi = 1.0 +\fISharplo\fR and \fIsharphi\fR are numerical cutoffs on the image sharpness +statistic designed to eliminate brightness maxima which are due to bad pixels +rather than to astronomical objects. +.le +.ls roundlo = -1.0 roundhi = 1.0 +\fIRoundlo\fR and \fIroundhi\fR are numerical cutoffs on the image roundness +statistic designed to eliminate brightness maxima which are due to bad rows or +columns, rather than to astronomical objects. +.le +.ls mkdetections = no +Mark the positions of the detected objects on the displayed image ? +.le + +.ih +DESCRIPTION + +DAOFIND approximates the stellar point spread function with an elliptical +Gaussian function, whose sigma along the semi-major axis is 0.42466 * +\fIdatapars.fwhmpsf\fR / \fIdatapars.scale\fR pixels, semi-minor to semi-major +axis ratio is \fIratio\fR, and major axis position angle is \fItheta\fR. +Using this model, a convolution kernel, truncated at \fInsigma\fR sigma, +and normalized to sum to zero, is constructed. + +The density enhancement image \fIstarmap\fR is computed by convolving the input +image with the Gaussian kernel. This operation is mathematically equivalent to +fitting, in the least-squares sense, the image data at each point with a +truncated, lowered elliptical Gaussian function. After convolution each point +in \fIstarmap\fR contains as estimate of the amplitude of the best fitting +Gaussian function at that point. Each point in \fIskymap\fR, if the user +chooses to compute it, contains an estimate of the best fitting sky value +at that point. + +After image convolution DAOFIND steps through \fIstarmap\fR searching +for density enhancements greater than \fIfindpars.threshold\fR * +\fIdatapars.sigma\fR, and brighter than all other density enhancements +within a semi-major axis of 0.42466 \fIfindpars.nsigma\fR * +\fIdatapars.fwhmpsf\fR. As the program selects candidates, it computes two +shape characteristics sharpness and roundness. The sharpness statistic +measures the ratio of the difference between the height of the central pixel +and the mean of the surrounding non-bad pixels, to the height of the best +fitting Gaussian function at that point. The roundness statistics measures +the ratio of, the difference in the height of the best fitting Gaussian +function in x minus the best fitting Gaussian function in y, over the average +of the best fitting Gaussian functions in x and y. The limits on these +parameters \fIfindpars.sharplo\fR, \fIfindpars.sharphi\fR, +\fIfindpars.roundlo\fR, and \fIfindpars.roundhi\fR, are set to weed out +non-astronomical objects and brightness enhancements that are elongated in +x and y respectively. + +Lastly the x and y centroids of the detected objects are computed by +estimating the x and y positions of the best fitting 1D Gaussian +functions in x and y respectively, a rough magnitude is estimated +by computing the ratio of the amplitude of the best fitting Gaussian at +the object position to \fIfindpars.threshold\fR * \fIdatapars.sigma\fR, +and the object is added to the output coordinate file. + + +.ih +EXAMPLES + +1. List the object detection parameters. + +.nf + da> lpar findpars +.fi + +2. Edit the object detection parameters. + +.nf + da> findpars +.fi + +3. Edit the FINDPARS parameters from within the DAOFIND task. + +.nf + da> epar daofind + + ... edit a few daofind parameters + + ... move to the findpars parameter and type :e + + ... edit the findpars parameter and type :wq + + ... finish editing the daofind parameters and type :wq +.fi + +4. Save the current FINDPARS parameter set in a text file fndnite1.par. +This can also be done from inside a higher level task as in the previous +example. + +.nf + da> findpars + + ... edit the parameters + + ... type ":w fndnite1.par" from within epar +.fi + +.ih +BUGS + +.ih +SEE ALSO +daofind, datapars +.endhelp |