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Andres,

Thank you for your most complete reply.

We are in complete agreement as respects Marc St.
Hillaire. Under yor comments on Latitude by Meridian
Transit, I would add only the comment that Course is
also relevant, which I feel sure you meant to include.

Regards,

Henry

--- Andres Ruiz  wrote:

> 
> [NavList 3635] Re: Marq St. Hilaire - Altitude
> intercept method:
> An accurate position is determined by meridian
> transit
> Latitude and subsequent Longitude by Time Sight,
> utilizing the accurate Latitude. In your opinion,
> will
> or will not an intercept determined by the Marc St.
> Hillarie method, utilizing the so determined
> accurate
> position, be equal to zero, If not, why?
> ------------------
> 
> Henry, if you know your exact position; Yes
> 
> The intercept is the great circle distance between
> the CoP based on calculated altitude, Hc, and the
> one based on the observed altitude, Ho. The
> calculate altitude is a function of the position.
> But Ho always has a little error, and the true CoP
> and the observed one may be different. 
> 
> If you use the St-Hilarie in an iterative way, the
> estimated position is not important, because you can
> improve it. Only the accuracy of the star shootings
> with the sextant is. And of course the knowledge of
> the conditions: temperature, pressure, height of the
> eye,
> The accuracy deepens only on the bodies and the
> measurements, not in the method. You can obtain a
> fix by iterative St-hilaire, by sight reduction with
> matrices, by T. Metcalf LS method or by Kaplan
> STELLA method, and the final solution in the case of
> two sights is the same. Also by Summer in an
> iterative way.
> If tree or more sights are involved, the solution
> can be different because the technique to obtain the
> most probable position is different.
> Using St-Hilaire in the old traditional graphic way
> to obtain the MMP, from a cooked hat, is the use of
> bisectors of the azimuth angle.
> 
> Meridian sight has tree main problems:
> 1. the maximum altitude
> 2. the time of the LAN
> 3. The speed of the vessel. (aboard a sailboat 4,8
> kn are insignificance)
> But taking a series of sight before and after the
> local noon, and adjusting them by a least squares
> method I usually get good results.
> 
> About accuracy, in coastal navigation is more
> important that in blue water, because the shallow.
> One friend of mine says: "Navigating, is not
> important to know where you are, the important thing
> is to know where you are not" (Is well expressed)
> 
> An example: some different AP and the effect of the
> improvement by iteration
> 
> 25/08/2004
> 22:00:00
> Enif
> GHA = 338.391817 � = 338� 23.5'
> Dec = 9.896533 � =   9� 53.8'
> Ho = 50.77
> Schedar
> GHA = 294.303014 � = 294� 18.2'
> Dec = 56.560600 � =  56� 33.6'
> Ho = 46.44
> 
> Result by exact 2 CoP solution, NA and Kaplan
> algorithm:
> B = 43.32162 =  43� 19.3' N
> L = -2.00219 = 002�  0.1' W
> 
> For AP:
> Be = 43.3166�
> Le = -2.0000�
> St-Hilaire:
> BI = 43.3216 
> LI = -2.0021
> HC     Z   p 
> 50.7749   141.4002    -0.0049
> 46.4378   47.7147 0.0022
> 
> For AP:
> Be = 41.5�
> Le = -3.5�
> St-Hilaire:
> BI = 43.3614
> LI = -2.0890
> HC     Z   p 
> 51.4421   137.8834    -0.6721
> 44.3881   46.1244 2.0519
> 
> For AP:
> Be = 30.0000 
> Le = -10.0000
> St-Hilaire:
> BI = 45.0388 
> LI = -5.5543
> HC     Z   p 
> 54.3421   117.6633    -3.5721
> 32.353    39.2049 14.087
> 
> After five iterations:
> HC     Z   p 
> 50.7700   141.4011    -0.0000
> 46.4400   47.7183 -0.0000
> 43.321611 N
> 2.002105  W
> 
> Best regards,
> 
> Andr�s Ruiz
> Navigational Algorithms
> http://www.geocities.com/andresruizgonzalez
> 
>
> 
> 


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