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Re: Why Not To Teach Running Fixes
From: Geoffrey Kolbe
Date: 2009 Dec 14, 21:46 +0000
John Karl wrote [NavList 11116]

The figure below (in [NavList 11116]) shows that they operate under extremely ridiculous
assumptions: They assume that the estimated DR track perpendicular to
LOP1 is completely accurate and that the DR component parallel to LOP1
is completely without value.  Can anyone on the List justify these two
assumptions??

To John's charge (caption to the diagram) that, "Infinitely many estimated track.... give the same RFIX..." I would answer that this is specious point. The important point is that an estimated DR track has two pieces of information: distance and course made good. Given this information, there is only one place we could put the advanced LOP. The navigator will know that at the time of the second sighting for LOP2, he will also be somewhere on the advanced LOP1. That is useful information, which can be used to derive a celestial fix.

I would make a general comment that a celestial fix is supposed to be an independent check on the EP. Therein lies its value. Of course, the wise navigator will seek to refine his final positional fix with whatever information is at hand, weighted appropriately. With this in mind, I have a few questions I would like to put to John.

John, in your diagram in [NavList 11116], you are combining information derived from celestial sightings with information otherwise obtained to derive EP2. You evidently think that the area of error around your original EP1 is smaller than the area of error around RFIX. What justification do you have for this assumption?

A related question is; what piece of information was it that persuaded you to move DR2 onto the line LOP2 to become EP2? Was it that you think the error of the sighting from which LOP2 is derived is smaller than the error around DR2? If that is the case, why can we not assume LOP1 to be just as accurate and so place more faith in RFIX than EP2?

Geoffrey Kolbe

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