[Issues] Satellite tracks not always detected

Ewout M. Helmich helmich at astro.rug.nl
Tue Nov 14 12:04:43 CET 2006


Well that sounds very good. I think the best course of action is simply 
to commit the changes to CVS. We can then have a look at it and update 
the eclipse installation here.

Ewout Helmich

Hans Vaith wrote:
> Dear all,
> when reducing data from the Sikkema dataset we found that satellite tracks 
> were not always detected. Looking at the python wrapper code of the Hough 
> transformation in SatelliteMap.py we did not find anything obvious, so I 
> started looking into the C code of the hough transformation in the eclipse 
> library. There seems to be a conceptual error or oversight. The 
> transformation code does not account for the possibility of negative values 
> for 'rho' (the perpendicular - or minimum - distance of the straight line 
> from the origin of the coordinate system). rho is always negative when the 
> offset of the straight line (b in the equation y = a*x + b) is negative.
> I corrected the code locally on my laptop installation of AstroWise and ran it 
> through the observations in question. All satellite tracks were then detected 
> correctly (one track additionally needed tweaking of the HOUGH_THRESHOLD 
> process parameter, because the path of the track through the image is very 
> short).
> Our basis was CVS version 1.4 of hough_transform.c We could send a patch or 
> our corrected source code, if there is interest. 
> Regards,
> Hans

Drs. Ewout Helmich             <><>
Kapteyn Astronomical Institute <><> Astro-Wise/OmegaCEN
Landleven 12                   <><>
P.O.Box 800                    <><> email: helmich at astro.rug.nl
9700 AV Groningen              <><> tel  : +31(0)503634548
The Netherlands                <><>

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