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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Eprf Vs, Trf
From: John Karl
Date: 2009 Dec 21, 21:26 -0600
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From: John Karl
Date: 2009 Dec 21, 21:26 -0600
Todd & Others,
It's because the TRF does not make use of the estimated track component along the advanced LOP1 (the same component of track parallel to LOP1) that LOP2 can completely control the distance along the advanced LOP1.
In addition to assuming LOP2 is accurate (which the EPRF assumes also), the TRF assumes that the component of the estimated track
perpendicular to LOP1 is the only information we have. (See 2nd figure in the 1st Dec 19th post.) I'm at a loss to know why, in an estimation problem, we should assume the DR track estimate is good in one direction and not another, particularly since these directions depend on the orientation of LOP1, which surely has nothing to do with the track accuracy.
The reason an advanced LOP1 or LOP2 gives nearly the same as EP3 is because the are nearly perpendicular to LOP3. The EPRF and TRF agree when the LOPs are are right angles. Compare with the 2nd figure in the 2nd Dec 19th post. There's not much agreement there. And it is easy to give examples where the differences are extreme.
JK
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