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    Re: Ellipse of Confidence in position finding
    From: Robin Stuart
    Date: 2019 Mar 17, 09:05 -0700


            The authors of the Nautical Almanac believe this to be 20 nautical miles. The method they describe in the section Position from intercept and azimuth by calculation on p.282 (2010) requires that the procedure be iterated until the initial and final estimates of position are within 20 miles of each other.

    “If d exceeds about 20 nautical miles set LF = LI, BF = BI and repeat until d, the distance between the position at the previous estimate and the improved estimate, is less that 20 nautical miles”

    The equations being used in the least squares calculation of position are exact in within the straight LoP approximation. The iteration is required to ensure that the approximation is a good one and that curvature of the LoP’s can be neglected,

    Robin Stuart

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