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I consider that the possible exposure of errors plotting/navigation
via the traditional RFIX to be of great value, and do see that a
navigator may indeed select your method of the EPRF for a given
observation. I still hold that the plotting and a considered
understanding of the two is of great utility in considering position,
however.

Consider that in traditional navigation, if all the explicit estimates
in your DRs and EPs and your LOPs were "correct", the RFIX and the EP
would agree to the Nth degree, and the positions they would plot would
coincide perfectly (perfection such as this is rarely if ever achieved
in the real world, and is usually reserved for classroom exercises.)
DRs (traditionally plotted with speed and course and no set/drift/
leeway component) would diverge from your EPs by the aggregated
estimates of set, drift and leeway. In the classic RFIX, the LOP is
advanced including set and drift calculations as is your EP.

If your EPs and RFIXs diverge significantly, it indicates an error in
estimating any or all of course, speed, set, drift and leeway
components, or error in your one or more of your LOPs, or in 'all of
the above'. Therein lies the value. The emergence of the divergence
gives you the opportunity and means to re-examine your plot and expose
the errors.

Your skill as a navigator will also allow you to select a means to
more clearly expose and resolve the uncertainty this divergence
represents. Typically you would determine the axis of the error (in
your example the error is predominantly east-west, so you would seek
an LOP from an eastern or western celestial body or a north or south
terrestrial sighting, either of which would plot as a north-south LOP)
and advance or retard the resulting LOP to reduce the uncertainty
between your EPRF and TRF and set out a new DR/EP track, perhaps with
revised assumptions on some of the input values.

Both of the EPRF and the RFIX are 'flawed' as you say -- at least in
that neither results in a 'FIX'. And yes, an advanced LOP does advance
parallel to itself, ignoring some possible inputs. That is the
geometry of navigation. Equally, the EP proceeds gaily ignoring cross-
track error, and other possible, perhaps unknown inputs. If your LOPs
are well selected, they will expose some of these errors over time by
combining 'speed' bearings (which plot near a right angle to your
track) and 'course' bearings (which plot nearly parallel to your
track).

However, to simply and blindly select either of the the EPRF or the
RFIX in all cases would, in my opinion, be a serious error in
practical navigation. A prudent navigator must consider all available
information at his disposal and seek new information to form the best
possible estimate of his position. I would respectfully suggest that a
consistently relying the EPRF as the sole or even preferred solution
ignores this approach.

Rob

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