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Here's a rum thing. On 1 Nov  I posted a Navlist message "Re: [Navlist
3728] Re: Direct methods." with a .rtf attachment. This attachment was
exactly the same that I had sent on 12 June 06, in the days of Nav-l, and
then it was successfully copied back to me as a .rtf file. No problems.

But today I took a look at the same attachment, reflected back to me
as Navlist 3731, from the message I sent on 1 Nov. It was still a .rtf
file with the same name "intersecting circles.rtf". But now, it's badly
corrupted, lots of spurious characters having been inserted, to make
nonsense of the thing. If your copy is larded all over with "=" signs, where
they clearly shouldn't be, as mine is, please don't try to make sense of it.
You won't. The basic text of the email itself was unaffected; just the
attachment.

To check whether it was just a one-off glitch, I will send it again attached
to this message; the text of my 1 Nov message is copied again below.

======================

d walden's first posting with its attachment came over successfully to me.
It may present problems to anyone that doesn't have Excel aboard as his
spreadsheet.


He wrote-

|    It is of course possible, as has been pointed out, to calculate the
latitude and longitude of the points of intersection of two circles of
position directly with neither an estimated nor an assumed position.  Nor in
fact are altitudes and intercepts or any plotting needed.  The intersection
of cones method, described by Frank in the discussion of latitude by lunars,
and shown in a previously posted FORTRAN and Maxima example can be used.  A
few minor changes to the programs posted are needed.
|
|  The problem is, in fact, slightly easier.  It can be done with
intersecting planes.  The attached little spread sheet is an example of how.
One enters with the altitude, declination, and GHA of two bodies.  Out come
the latitudes and longitudes of the two intersection points.  If you have
three bodies, pick a different pair, and two of the points should wind up
quite close.  There you are.
|
|  Seems to be working for me, but no guarantees.

===================

For completeness, if nothing else, I resend an attachment which originally
went out to the old Nav-L list on 12 June 06, under the threadname
"positions from crossing two circles". That provided a routine, written in
Bastard-Basic for a Casio pocket-calculator, to determine the two possible
positions that result from crossing two observations. It also explains how
the thing works.

I remember that Andres followed it up with a posting in which he had
converted it to a program written in C.

George.

contact George Huxtable at george@huxtable.u-net.com
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.

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