NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Andrés Ruiz
Date: 2009 Jun 9, 12:21 +0200
When I was a child, my first contact with celestial
navigation was getting the latitude at noon. But my position was not
determined, and I try to obtain the longitude also at noon, I have very good
memories of that time.
Apart of the restrictions of the method, well known
today, there is no doubt about its great educational value.
Obtaining the position at meridian passage has for me
the savour of the old days, and a special affection because this method
introduced me into the amazing world of the navigation.
After this introduction I wish to share a program
that I have written to calculate the fix at noon.
The method is the following:
1. Least squares fitting - The curve equation is: H =
a0+a1*t+a2*t2
The maximum gives:
t max = -a1/(2a2)
H max = a0-a2t2
2. TimeOfLAN = tHmax + delta_t
POSITION FROM OBSERVATION OF A SINGLE BODY James N.
Wilson Vol. 32, No. 1, 1985
3. Position( TimeOfLAN ))
Dec( TimeOfLAN ))
GHA( TimeOfLAN ))
Ho = yLS( TimeOfLAN )
( Dec, Ho, culmination ) -> B_LAN
GHA -> L_LAN
I have tested the results under simulated data, and
the results are OK.
The attached pdf is a real example. The source of
error, compared with the GPS position, is due to the fact that the sextant
observations were made under bad conditions, and an autopilot consisting in a
rope attached to the tiller!!!
I cannot do an observation on the beach near my home,
because at LAN the Sun is at the south and the horizon is towards the north,
maybe I try to use an artificial horizon.
For those who wish to play with the program, I can
send an add on for my software, available at my Web site (900KB).
The input files can be generated semi-automatically
or manually. I shall have to write some instructions…
Regards,
Andrés Ruiz
Navigational Algorithms
http://www.geocities.com/andresruizgonzalez
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