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Aubrey O'Callaghan said, referring to section 11, "Position from intercept
and azimuth", in the Nautical Almanac"-

>I wondered if this was the same algorithm as in the Almanac, it was
>something I was going to check tonight, but now it's confirmed
>That being said, I remember plugging this formula into a spreadsheet (on a
>Psion 3A - I was at anchorage by some Caribbean island at the time)
>I then placed my initial position nowhere near where I was. After about 3
>iterations it converged to my actual position. I was quite surprised as I
>had thought that one's initial guess should be approximately where one is
>(at least within a few degrees). I even tried different hemispheres as
>starting position.

There's a bit of extra information about that matter, given in section 7.4
of the AstronavPC booklet, but not in the Almanac, as follows-

"It is possible, but not advisable to start the iterations with a position
that is in a different hemisphere. Provided L(I) is kept in the range
-180deg to +180deg and B(I) in the range -90deg to +90deg the solution in
most cases will begin to converge after a few iterations."

That seems pretty all-embracing, doesn't it? But it is a bit odd, because
L(I) and B(I) are the improved values, not the first values which are L(F)
and B(F). I think the statement above could only make sense if it was
intended to apply to L(F) and B(F).

By the way, I hope it's obvious that where I have written L(F) is where the
original document had L with a subscript F, and so on.

George.

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