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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Eprf Vs, Trf
From: Geoffrey Kolbe
Date: 2009 Dec 20, 09:33 +0000
From: Geoffrey Kolbe
Date: 2009 Dec 20, 09:33 +0000
John [NavList 11289] posted a re-capitulation of his EP running fix method as preferable to the Traditional Running Fix, where a new EP is taken to be where the LOPs intersect. Of the two diagrams John attached to his post, he says: As you can see, uncertainly in the EPRFs are continually >corrected, and limited, by succeeding LOPs. For comparison, the 2nd >figure shows the TRF results using the same LOPs and DR estimates. >The track and fix locations vary radically, with some fix locations >beyond possibilities. (Also the TRF is even a bit more messy and more >plotting work.) I not sure that this is right. In the EPRF diagram, the area of uncertainty on the final DR position is just the same as on the first. If the area of uncertainty is due to errors in course held and distance run, we would expect the area of uncertainty to grow correspondingly with each successive fix. Pretty soon, the areas of uncertainty would grow so that it would not matter which method you were using, EPRF or TRF. The only circumstance in which John's proposed constant area errors would be a correct would be if that was the error in the original position (not shown) and all subsequent errors in course held and distance run are small compared to this original area of uncertainty. I also note that the new LOP always manages to go through the area of uncertainty on the current DR. What if it did not? What would John do then? Geoffrey Kolbe -- NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList+@fer3.com