NavList:

   

Reply

The construction is based on the fact that

1. Periphery angles over the same arc are equal

and

2. The central angle is twice as large as the periphery angle.

Therefore, for any given chord, the locus of all points from which that 
chord is seen under a given angle is a circle. The center of that circle 
is on the bisector of the chord, exactly in the place from which that 
chord is seen at twice the given angle.

Of course, said circle is a LOP. (The claim on the referred website that 
a position can be derived without LOPs is misleading.) In order to get a 
position, one must combine this circle with any other suitable LOP, 
which may or may not be obtained in the same way.

The horizontal angle between the two chosen landmarks can be measured 
directly with a sextant or as the difference of two compass bearings. 
The former has the advantage of increased accuracy (minutes of arcs 
instead of degrees). I believe there is a plotting tool specially 
designed to assist with the method. I have never seen one in natura, but 
it's some kind of a rule-plus-protractor with three arms that can be set 
to the given angles.

Herbert Prinz




NavList@aol.com wrote:

>
>I have found an intriguing example of triangulation from a 16th century 
mathematician, Willebrord 
Snellius(http://www.sailingissues.com/navcourse4.html). I have searched other 
web sources on the web and so far, have had no success in finding a straight 
forward explanation of how this method of triangulation works. Have any of 
you actually used the "Snellius Construction" technique, and could you help 
me understand it as a practical navigation application?
>
>Thank you,
>
>Todd Frye
>
>-----------------------------------------------
>[Sent from archive by: fryefamily-AT-sisna.com]
>
>
>>
>
>  
>




--~--~---------~--~----~------------~-------~--~----~
Navigation List archive: www.fer3.com/arc
To post, email NavList@fer3.com
To , email NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---

   

Reply