NavList:

I did this around noon on 5/28.  I will post the graphical solution.  I unfortunately cannot do the same for the sunlines (I used a computer program to reduce them).  The position is VERY accurate in this case.  I cannot say for other places or circumstances.

 

One of the biggest challenges is getting a uniform series of sights.  If you are not very accurate in your series (error jumps from one to the next) it will greatly skew your results, especially away from noon when the Zn changes slowly.   Since there is little change in the direction of the LOP's it is difficult to determine an exact position (in the AM/PM hours it will be hard to determine Latitude.)

 

Jeremy

 

In a beta version my software CelestialFix, a simplified algorithm of Kaplan's [1] is implemented, (the core of the STELLA [2] USNO software, used with a star-tracker).

Sights have inside information about the position, course and speed of the observer, and the algorithm solves the general problem in an engineering way. One of the great advantages is that the advance of the circles of equal altitude is taken into account automatically.

I have tested it with a simulator and the solutions are good solving for position, and for position & motion. With real sights: ten taken over 40 min aboard a sailboat, 3/5 Kt, the solution for position is really good, but it isn't when including motion, I think because the course and speed were not constant during the time of shooting the Sun. Is it very difficult to maintain a constant motion when sailing. Aboard a motor vessel, freighter, ..., the thinks maybe go well, but I don't know...

For someone who wishes to test the program, I can send it by e-mail under request (5.7 MB)

Andrés

[1] Kaplan, G. H. (1995): "Determining the Position and Motion of a Vessel from Celestial Observations", Navigation, Vol. 42, No. 4, pp. 631-648.
[2] http://www.dtic.mil/dticasd/sbir/sbir021/n104.pdf


-----Mensaje original-----
De: NavList@fer3.com [mailto:NavList@fer3.com] En nombre de frankreed@HistoricalAtlas.net
Enviado el: domingo, 25 de mayo de 2008 13:41
Para: NavList@fer3.com
Asunto: [NavList 5129] Re: Navigation exercise


By the way, have you ever considered the general problem of taking a series
of Sun sights in relatively rapid succession (at an arbitrary time of day,
not necessarily around noon)? For example, suppose it's 1500 local time. If
I take ten sights over half an hour, what kind of position fix can I get?
This is a generalization of the "sights around noon" problem. There's no
easy graphical solution but it's similar in other respects.
--~--~---------~--~----~------------~-------~--~----~
Navigation List archive: www.fer3.com/arc
To post, email NavList@fer3.com
To , email NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---