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    Re: Avoiding the symmedian (and other) points
    From: Bill Lionheart
    Date: 2018 Nov 6, 21:54 +0000

    Well the least squares point (MPP) of two lines is where they cross.
    But the elliptical probability contour is still defined, and the
    ellipse is not a circle if the LOPs do  not meet at 90 degrees
    See for example
    Stansfield, R. G. "Statistical theory of DF fixing." Journal of the
    Institution of Electrical Engineers-Part IIIA: Radiocommunication
    94.15 (1947): 762-770.
    which includes the case n=2 lines
    Bill Lionheart
    On Tue, 6 Nov 2018 at 03:03, Gary LaPook  wrote:
    > I made the sugestion several times in the past that the way to avoid all the 
    discussion and desention about finding the proper point to represent the 
    "fix" in a three-star "cocked hat" was simply to only observe two stars. It 
    appears that this is the method used by the Air Force in its automated 
    star-tracker systems, only using two stars at a time. And it acheives better 
    than a 1,000 foot CEP. This means that 50% of the fixes will be within 1,000 
    feet, 93,7% will be within 2,000 feet, and only 0.2% will fall outside of 
    3,000 feet. The automatic star tracker is sugested for surface Navy ships 
    but, for surface navigation, the same old problem of clouds raises its ugly 
    head. At 25,000 feet the probability of a clear line of sight anywhere on 
    earth and at any time is 68% and becomes 100% at higher altitudes. Would it 
    were it this good on the surface!
    >  http://www.dtic.mil/dtic/tr/fulltext/u2/a090649.pdf
    > gl
    > View and reply to this message

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