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% @(#)fit_ell2.hlq 19.1 (ESO-IPG) 02/25/03 13:30:32
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FIT/ELL2 17-Feb-1992 RHW
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FIT/ELL2 inframe pol_opt iso_tol iso_levels [center[ [radius] [sky_level]
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fit an ellips with respect to predefined center
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Purpose: An image is searched for intensity points within a certain
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intensity range and within a radius to the center.
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Syntax: FIT/ELL2 inframe pol_opt iso_tol iso_levels [center[ [radius]
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polar_opt = 0, if polar frames should be made (first run)
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1, polar frames already exist (repeated runs)
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iso_tol = isophotal tolerance in promille of iso_levels
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iso_levels = isophotal levels you want to fit (max = 10)
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the format can be low:high:incr or lev1,lev2,..
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or a combination of the two separated by a comma
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center = x,y-coordinate of center of object; default is the
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value used in the previous run
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radius = radius around center to be surveyed; default is
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value used in the previous run
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sky_level = value to be added to the iso_levels before a fit
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is made to the data points; default is the value
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Note: The input image should have been cleaned from disturbing objects
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(stars) in the region of interest. The center of the object can
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be calculated using the command CENTER/GAUSS.\\
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The ellipses are fitted with respect to the predefined center.
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At high isophotal levels the fit will be affected by the seeing
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and it will become round, the position angle being undefined.
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At low isophotal levels (< 5 - 2 %) the affect of noise is that
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of a round object. With these natural restrictions the code
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allows to trace isophotal twisting.\\
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Points that were found and lay exactly on the ellips can not
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be discriminated from the ellips.\\
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The parameters of the ellips are communicated to the user.
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The command creates two polar coordinate frames containing the
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polar coordinates radii and angles of every pixel of the input
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frame. The polar coordinates of the points found are used to fit
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an ellips with a predefined center. Every rerun of the program
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(with polar_opt=0) will delete the preexisting scratch files of
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the polar coordinates.
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The command also produces an image called ELLIPS with the points
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used for the fit and with the actual ellips determined. This image
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can be used for display. Different isophotal levels will displayed
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in different colours. In the examples below the use of this file
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together with the input data file is demonstrated.
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FIT/ELL2 INFRAME 0 10 10:50:10 -356.,-456 1000 125
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and run again bad solution for the 50_isophote changing the
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FIT/ELL2 INFRAME 1 30 50
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or run again changing the radius of the search area
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FIT/ELL2 INFRAME 1 10 50 300
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etc. In this way one can interactively steer the fit
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towards optimal solutions.
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{\tt FIT/ELL2 INFRAME 0 10 10:50:10,70,90 -356.,-456. 1000 0\\
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LOAD/IMAGE INFRAME 0\\
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LOAD/IMAGE ELLIPS OVERLAY\\
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{\tt FIT/ELL2 INFRAME 1 10 10:50:10,70,90 -356.,-456. 1000 0\\
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LOAD/IMAGE INFRAME 0\\
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LOAD/IMAGE ELLIPS OVERLAY\\