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    Alternative to running fix
    From: Paul Hirose
    Date: 2000 Aug 05, 5:31 PM

    Instead of advancing a line of position by several hours for a running
    fix, why not use it to improve your estimated position immediately?
    Bowditch shows how in the chapter on celestial LOPs. First plot the
    LOP and your estimated (or DR) position at the time of the LOP. Then
    your new EP is the point on the LOP that's closest to the old EP.
    
    Plotting is easier this way because only the EP needs to be advanced
    to the time of the next LOP. As long as you have a good mix of LOP
    angles, I bet you could navigate forever, never take a fix, yet keep
    your DR real close. Just take a few sun sights each day and update
    position after each one. I don't see anything but advantages compared
    to a running fix. Nobody else has suggested this, though, so I guess
    there's a flaw in my reasoning somewhere.
    
    I do think a computerized nav system (something way more costly than a
    Celesticomp) would immediately integrate a LOP into the present
    position solution, and not save it for a running fix later. But I have
    to admit I've never worked on a system that dealt with discrete LOPs.
    In my experience, the sensor, such as doppler, puts out continuous
    data. A closer analogy would be ground mapping radar, which does yield
    discrete data points, but they are fixes, not LOPs.
    
    One airplane I used to maintain had buttons marked QUAL 1 and QUAL 2
    so the navigator could tell the computer how much confidence he had in
    his radar crosshair placement. Interestingly, even when you hit QUAL 1
    the system wouldn't simply slave its present position to the crosshair.
    It would weigh its own dead reckoning ability against your likely
    accuracy, and accept some of your input. If the correction was
    unreasonably large, the computer figured you had the crosshairs on the
    wrong point, and would reject the update. There was a button to
    override that, but even then the computer got the last word. It would
    update its position but not its velocities. That way a botched fix
    would introduce a fixed error but one that wouldn't grow with time.
    

       
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