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    Re: The "Death to the Intercept Method" revisited?
    From: Jing C
    Date: 2017 Sep 5, 11:22 -0700
    I think there is conflating going on of two issues. One is two sights taken at different times but from the same place, which is solvable by those equations for direct calculation of latitude and longitude. The separate stickier issue is the running fix, taking two sights that occur at two different times AND two different places. 

    Robin's paper deals with the second, and I think Andres has a paper detailing vector solution for the same issue. I read Robin's paper, and I like the concept of ditching advancing LOPs and instead iteratively solving for a constraint of three conditions. My gut still refuses to believe in the distortion caused by moving a circle of position though; I'll have to work through some examples step by step to convince myself.

    Unfortunately, I don't think either Robin's solution or Andres's solution for the running fix can be implemented on a normal scientific calculator. (Maybe a graphing calculator?)

    On Sep 5, 2017 10:05, "Francis Upchurch" <NoReply_Upchurch@fer3.com> wrote:

    Hi Tony,

    I've always got the correct answer without adjusting everything for "simultaneous" altitudes.

    See attached, which I think explains the principles. Main quote from this:

    The development of the direct fix given above is robust and exact for observations taken from the same place. The observations need not be simultaneous (although they might be with observers side by side, or with a double sextant, but their times must be registered accurately so that the GPS of the bodies at the times of their altitude measurement can be found in the almanac. The observations need not even be taken on the same day. Typically, two sights could be 1 or 2 min apart on two different bodies. The two sights could also be on one body, such as the sun...

    Hope this helps. Apologies if I have this wrong, but it seems to work for me.

    Best wishes

    Francis



    Attached File:
    timesightfix.pdf

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