SatCal with Astrometry Function

From: Gerhard HOLTKAMP (
Date: Wed Jun 16 2010 - 20:15:24 UTC

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    A simple astrometry function has been added to SatCal. You can now load 
    pictures with satellite trails on them. Once loaded a picture will have to be 
    initialized by clicking on three stars and entering the respective sky 
    coordinates. (This is the bottleneck of the whole operation as it has to be 
    done manually.)
    Once initialized you can then click on the endpoints of a satellite trail and 
    have SatCal calculate an approximate (circular) orbit fitting the trail as 
    well as checking which objects of the currently loaded TLE file (typically 
    the Spacetrack ALL_TLE) might fit the trail. (This may have to be repeated 
    checking the reverse direction as well unless you already know whether the 
    satellite was moving left to right or right to left along the trail).
    The candidate objects thus found can then be displayed to move across the 
    picture just as they otherwise would move across the standard world or sky 
    map and you can see how the objects fit the trail.
    Just don't get too excited about this. If you want to check the identity of a 
    single satellite you saw it is normally much faster to just check which 
    objects passed the approximate direction at the right time rather than going 
    through the process of identifying three reference stars. But there are three 
    cases where this new feature could be useful:
    You have multiple trails on a picture and have to sort out the various 
    You take a series of pictures of the same part of the sky. If you can use the 
    same reference stars you have to supply the respective coordinates just once. 
    On successive pictures it is enough to just click on the reference stars as 
    the last set of coordinates will have been remembered. Initializing these 
    follow-on pictures is thus a matter of seconds.
    You want to investigate flares. In this case you typically know the identity 
    of the satellite and can load it directly and have it move across the picture 
    while displaying the orientation of the surface which would cause a maximum 
    flare at that moment. Checking it along the trail you can then have an idea 
    which surface might have flared.
    Anybody interested can download a Linux or Windows Version of SatCal 11.0 from
    Windows users might encounter a problem when trying to load JPG files. I 
    haven't been able to figure out why because it runs correctly on my own 
    Windows system as well on all the different Linux distributions I've tested 
    it. If you are affected by this problem you would have to convert the JPG 
    file into a PNG file first which can be done by almost any image processing 
    Gerhard HOLTKAMP
    Darmstadt, Germany
    Seesat-l mailing list

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