NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Eprf Vs, Trf
From: John Karl
Date: 2009 Dec 22, 12:17 -0800
From: John Karl
Date: 2009 Dec 22, 12:17 -0800
On Dec 22, 10:25�am, NavL...@fer3.com wrote: > John, > > I think that we are discussing 2 different things. No, we're discussing the same thing -- the estimation logic of the TRF compared to the EPRF. > You ask why we are ignoring the estimated track along LOP1. � That's because I don't trust the _starting_ point of the track along LOP1. �Advancing an untrustworthy position seems pointless. We always have some idea where we are along LOP1. The EPRF retains that info, no matter how poor it might be, while adopting the constraint of the new LOP. Can't do better than that. > It comes down to how well do you trust the EP1 position and why. If you have good information or a fairly recent fix to base the DR track from, then EP1 is trustworthy and useful. �If the DR track is old with no other information, then the EP1 is useless. No, the EP uses all the information in the new LOP, and retains the DR info that in not contradicted by the new LOP. Can't do better than that. The DR track isn't old, it's the best and latest info we have until a new LOP is acquired. > My point about using LOP2 crossing LOP3 was that when you have 2 LOPs that cross at reasonable angles, then there is not much difference between the EPRF and the TRF. �Looking the that diagram from Dec 19, �RFIX3 and EP3 show good match. �RFIX4 would have been much better if plotted using LOP2 with LOP4. As I noted several times, the TRF and the EPRF increasingly agree as LOP angles approach 90 degrees. > To summarize, > > Why do I trust the DR track that gives me EP1 ? We don't "trust" it. It's simply the best info we have until get a new LOP. > Is there a previous fix or LOP that I can use ? We always know something about where we are, that's our current DR position. > If I have a trustworthy DR and only LOPs that cross at small angles. �I would use the EP as you show. Until I get an LOP that crosses well. When they cross well, it doesn't matter which is used. The EP is a bit easier. > If I don't have a trustworthy DR they I will need a couple of LOPs that cross at a large angle before I start to trust any of my position estimates. The EPRF gives the best estimate in the mean time. JK -- NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList+@fer3.com
