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    Re: sight reduction with GPS receiver
    From: Herbert Prinz
    Date: 2005 Mar 18, 19:16 -0500

    Paul Hirose has surely found the most sophisticated way of landing in
    the reefs with the combined assistance of GPS _and_ a sextant! A GPS
    receiver normally shows distance between two points along the geodesic.
    For the points in the given example the answer using WGS84 is 2229 nm,
    being 3 miles off the GCD. In a worst case scenario, (e.g. establishing
    latitude at N45 from the sun at winter solstice) the discrepancy is 20
    miles!
    
    In order to use your GPS receiver as a makeshift sightreduction
    computer, you have to cajole it into using a spherical earth model. On
    some models this is not a trivial task - if possible at all. (To say
    nothing of the practical aspect of making sure that a GPS receiver that
    has been upset in such a fashion does not end up in the nav station by
    mistake, quasi as a time bomb ready to explode at the moment of
    landfall. But practical aspects hardly play any role in this discussion.)
    
    Herbert Prinz
    
    Paul Hirose wrote:
    
    >There are other ways a GPS receiver can assist with traditional
    >navigation. For example, let's try a sight reduction.
    >
    
    
    

       
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