# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: AP terminology, WAS: 2-Body Fix -- take three
From: Andrés Ruiz
Date: 2009 Nov 19, 08:29 +0100

Jeremy, I use the same technique for plotting the LoPs, for the same reasons.

One of my main reasons for start programming the nautical calculations was in a small sailcraft you are the mariner, the pilot and the captain, and is very very difficult to do the SR without errors when on sea.

The other, is very good way to dissect the problem and learn about it.

Andrés Ruiz

De: Anabasis75---.com [mailto:Anabasis75---.com]
Enviado el: martes, 17 de noviembre de 2009 18:05
Para: navlist@fer3.com
Asunto: Re: [NavList 10725] Re: AP terminology, WAS: 2-Body Fix -- take three

Since JK finally explained what he meant my calculating LOPs "directly" I agree with him to a point.  When using a calculator for my celestial triangle reductions (which I do for a vast majority of my work at sea if it is not done on the computer), I certainly could use the DR/GPS fix as the AP for each star and then calculate and plot each star line from the azimuth and intercept from this position.  The trouble with this in a practical sense is the mess it makes when plotting manually.  I prefer to advance my lines in a way we do with radar LOP's.  I advance or retard each AP and plot from there.  This gives me a clean fix near my track.  If I were to try to advance the DR I would have a mess near my track and might be confused with the previously plotted LOP's.  It is even worse when you plot the original lines then try to advance them as you cross your track.  When my computer plots this, it is much easier, and I use his "Combined" method for nearly all of my star fixes.

In conclusion, there are a lot of practical considerations as to why a particular method is used to determine position at sea that goes far beyond the reduction of the celestial triangles, especially when you are using more primitive tools.

Jeremy

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