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+.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