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    Significance of azimuth errors, was : Principles and Being Practical
    From: Trevor Kenchington
    Date: 2003 Sep 7, 10:17 -0300

    Geoffrey Kolbe wrote:
    > I also wonder just how much of a problem it would cause having your
    > near-prime-vertical azimuths off by around 15 degrees? [snip]
    > If your estimated position is pretty close (say, within 10 nautical miles)
    > to your actual position then I cannot think of any circumstances where it
    > would significantly affect the sort of accuracy we would expect from CN in
    > a small boat at sea
    A 15 degree error in azimuth and an intercept of 10 miles would place
    the point where the LOP cuts the azimuth 2.7 miles from where it should
    be. However, the LOP would then be plotted perpendicular to the
    erroneous azimuth. The distance from the plotted azimuth to the point
    where the LOPs cut could be considerable, depending on angles between
    the azimuths of the observed bodies, whether all intercepts are towards
    (or away) versus some one and some another, and whether the other
    intercepts are small or large. Hence the position of the LOP where it
    approaches another LOP could be out by several miles -- or by nothing at
    all if the other LOP lies where the erroneous one cuts the line that it
    should have followed, in the absence of the azimuth error.
    Then there is the question of the angle of cut of the LOPs. If two cut
    at right angles, an error in bearing of one of them would have the least
    effect but a more acute angle of cut would greatly increase the error.
    Of course, there is some chance that this one error in azimuth would
    cancel some other errors and move the fix closer to the true position.
    It is also true that a round of sights, producing four or more LOPs,
    might indicate that this one LOP is unreliable.
    Still, I'd rather not have the potential for a 15 degree error in
    azimuth in my sight-reduction method.
    Trevor Kenchington
    Trevor J. Kenchington PhD                         Gadus{at}iStar.ca
    Gadus Associates,                                 Office(902) 889-9250
    R.R.#1, Musquodoboit Harbour,                     Fax   (902) 889-9251
    Nova Scotia  B0J 2L0, CANADA                      Home  (902) 889-3555
                         Science Serving the Fisheries

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