NavList:

John,

I think that we are discussing 2 different things.

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.

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.

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.

To summarize,

Why do I trust the DR track that gives me EP1 ?
Is there a previous fix or LOP that I can use ?

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.

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.

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