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The fundamental reason for the AP is to solve an otherwise difficult
problem. The AP gives the 3rd piont of a triangle. This results in a
solution to angles at the AP that can be compaired to the observed
angles measured at the real  location.  The differance between the AP
and the observers location results in a known for the observer.
Without the AP the angles between the pole and the GP of the cel. body
can't be known. So weather the AP is the DR or not is not the
important point. The point is that the use of an AP is the thing that
gets the geometry done.

Thomas A. Sult, MD
Sent from iPhone

On Nov 11, 2009, at 21:13, Peter Fogg  wrote:

>
> John Karl wrote:
>
> Ahhhh Frank, see what I mean----
>
> All these posts, and look at the confusion:  The DR is an AP, it's one
> particular choice of an AP.  And tables have nothing to do with it.
>
> Beg to differ, John. To start with, where is the confusion we should
> be looking at?  I don't see it.
>
> Next, the AP involves an artificially assumed position for the
> convenience of some tables entry, much as Jim has explained (without
> succeeding in confusing me - your mileage may vary).  Adopting the
> DR involves use of the best estimate of position with the intercept
> method.  Different.
>
> Only by trying to merge these different positions into one, as per
> your: "The DR is an AP" could confusion be created, which might be
> one good reason so not to do.
>
> Has anyone answered the question WHY we use an AP in the intercept
> method??
>
> Could Jim have already done so?  For convenience of some tables entry?
>
> To phrase it another way, since we know everything needed to
> calculate the celestial LOP (the GP's location and the altitude), why
> not just calculate the LOP directly?
>
> We're tuned in and awaiting the answer with bated breath, John.  The
> floor is yours..
>
> >

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