Re: [dsat] Location: GPS vs Chart?

From: Björn Gimle (b_gimle@algonet.se)
Date: Sat Apr 12 2003 - 04:24:14 EDT

  • Next message: Leo Barhorst: "Obs april 11"

    It's a terrible error for any GPS or map (if arcsecond -or even
    arcminute- accuracy appears possible), and there is no (known) reference
    system that has such an offset !
    
    The error is about 4 km N-S, 7 km E-W, or about 0.5 degree at 800 km
    range.
    
    That is usually fully acceptable if you report an UNID, or an obs where
    the elset is minutes in error because it is a satellite near decay, or
    you recover a "lost" classified satellite after a long period in
    daylight/shadow.
    
    It is also sufficient for an analysis and prediction of flashes from a
    spinning satellite - not for an operational Iridium where pointing
    accuracy is much higher and necessary for accurate prediction.
    
    For a geosynch (flasher?) it would give only 0.01 degree error - quite
    acceptable even for a positional obs, more than enough for flash
    prediction.
    
    ----- Original Message -----
    From: "Curt Porter"
    
    >    I wonder where I really am. My LAT/Long is
    > 36 12 34N   86 42 13W  via the U.S.G.S. quadrangle charts
    > but get different figure with a GPS. Could the charts be wrong?
    > Or maybe the man had a cheap GPS?
    >
    > Changing to decimals:
    >
    > chart GPS
    > 36.2094N 36.166N
    > 86.7036W 86.784W
    >
    >    If I were to post data points for satobs I realise this
    > would throw the calculations off. Is it a significant error?
    
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