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Significance of azimuth errors, was : Principles and Being Practical
From: Trevor Kenchington
Date: 2003 Sep 7, 10:17 -0300
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@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 http://home.istar.ca/~gadus