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    Re: accuracy of automatic celestial navigation
    From: Robert Eno
    Date: 2002 Dec 8, 12:52 -0500

    Hello Mr. Geers,
    
    Have you an address, internet or snail mail, to where one can direct a
    request for reprints?  This sounds like very interesting stuff.
    
    Robert Eno
    
    ----- Original Message -----
    From: Glenn Geers 
    To: 
    Sent: Saturday, December 07, 2002 5:08 PM
    Subject: Re: accuracy of automatic celestial navigation
    
    
    > On Sat, 7 Dec 2002 05:18 pm, you wrote:
    >
    > The algorithms used in STELLA have been published. The author is George
    Kaplan
    > former head of the Astronomical Applications Department at USNO. I have
    the
    > full set available (have to dig them out). The USNO will provide reprints
    of
    > the papers that aren't available on the web. It's pretty neat stuff. The
    > algorithms take the motion of the vessel into account and can provide very
    > high (30m) accuracy.
    >
    > Also of interest: Polaris subs of the 60's carried an automatic astro-nav
    unit
    > that they used to reset their inertial systems from time to time. Most
    auto
    > systems use infrared optics so they can track stars during the day.
    >
    > Regards,
    >         Glenn
    >
    >
    > > On Friday, December 6, 2002, at 04:05 PM, George Huxtable wrote:
    > > > For those of us that sail our small craft out at sea, my opinion is
    > > > that if we can achieve a precision of 2 min, we are doing pretty well.
    > > > What do others think?
    > >
    > > I would agree.  2 nmi at sea is very decent; on land we should be able
    > > to get to 1/2 mile or better.
    > >
    > > On land I recently took a string of shots using a Tamaya Jupiter
    > > sextant with a 7X scope.  I shot the sun mid afternoon over a period of
    > > 20 minutes.  (This was on the coast of Oregon at a beachhouse on the
    > > water.)  I used a Garmin GPS in averaging mode to determine my actual
    > > position to 15 feet or so.  The resulting intercepts in nmi are
    > > interesting to analyze.  Because my assumed position is known to within
    > > 15 feet, these can be taken as errors in my sights.  Here they are in
    > > order:
    > >
    > > 0.91
    > > -0.06
    > > 0.59
    > > -0.05
    > > 0.22
    > > 0.55
    > > 0.22
    > > -0.28
    > > -0.53
    > > -0.57
    > > -0.77
    > > -0.03
    > > -0.19
    > > -0.11
    > > -0.43
    > > -0.62
    > > 0.27
    > > 0.24
    > > 0.44
    > > 0.25
    > >
    > > The mean of the intercepts is a mere 0.0025 nmi -- very good -- but the
    > > individual readings varied over a 1.68 nmi range -- not so good.
    > >
    > > When we are "warming up" and we haven't used our sextants in a while I
    > > find that the first shots are often in greater error than later sights.
    > >   This is in fact the case with this set of shots shown above: the worst
    > > error came from the very first sight.  Therefore I have found that it
    > > is wise throw out the the first reading or two, or at least to discount
    > > them.
    > >
    > > Other experiments I have done:
    > >
    > > I took five shots in my backyard using the same sextant and an
    > > artificial horizon and got a 1.27 nmi range of errors and a mean error
    > > of 0.644 nmi.
    > >
    > > I took fourteen shots in my backyard using a Tamaya Venus (not nearly
    > > as powerful of scope) and an artificial horizon and got a 4.3 nmi range
    > > of errors but a mean error of -0.45 nmi because of the greater number
    > > of sights taken.
    > >
    > > And for my finale, one afternoon I used six different sextants in my
    > > backyard and I took a total of 46 sights using an artificial horizon.
    > > I got an 11.2 nmi range of errors with a mean error of
    > > -1.23 nmi.
    > >
    > >  From this the statistical nature is shown to be very useful: although
    > > any one shot could be in error up to almost a mile, a series of shots
    > > averaged does indeed improve accuracy to very good levels; STELLA
    > > appears to do this, and thus an automated system is very appealing.
    > >
    > > Dan
    >
    >
    
    
    

       
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