# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

**Re: Snellius Construction questions**

**From:**John Karl

**Date:**2009 Jan 5, 19:44 -0800

One way this Snellius construction can be understood is by first understanding the case a single LOP that results from the horizontal angle between two markers B & C (buoys, etc.). If you measure a horizontal angle A between the two markers, your ship is on a circular LOP with radius R = a/(2sin A), where a is the distance between the markers. The three locations, B, C, and the ship, all lie on this circular LOP. You can can find the center of the LOP circle by striking arcs of radius R from both markers; then draw the LOP with radius R centered on this point. Alternatively, as the website shows, the center of the LOP circle can be found by the construction line they laid out at angle A from the B- C connecting line. By drawing the special case where the line from one marker (say B) to the ship passes through the center of the circle, you can see that a right triangle is formed, B-ship-C, with the right angle at C. You'll also see that the perpendicular bisector of the B- C line must passes through the center of the LOP circle. By studing the angles in this figure, you can understand their construction. It's tough without graphics and hand waving, John Karl On Jan 5, 2:43�pm,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@googlegroups.com To unsubscribe, email NavList-unsubscribe@googlegroups.com -~----------~----~----~----~------~----~------~--~---