NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: AP terminology
From: Geoffrey Kolbe
Date: 2009 Nov 15, 08:07 +0000
From: Geoffrey Kolbe
Date: 2009 Nov 15, 08:07 +0000
Frank, Peter H and Peter F. The confusion comes from a loose (I hesitate to say incorrect) use of terminology. Peter Fogg is right, I think, that because the tables generally used for sight reduction require an Assumed Position, this term has degenerated into a generic term for the starting position when using the St Hilaire method - but that does not make it the "correct" term. Frank has a point, that we bring the baggage of our backgrounds with us when getting to grips with new concepts and problems and this can cause confusion. Peter Hakel tells us that his background is as a "theoretical and computational physicist (in the area of radiative properties of plasmas)". As I did my Ph.D. in the radiative properties of (atoms in) plasmas, there is no excuse there ;-). My problem was the term 'LOP'. To me, an LOP (or position line as we call it over here) is a straight line. We must remember that the St. Hilaire method is essentially a graphical method where a fix is generated by drawing lines on a chart. The LOP's drawn on the chart are lines which are tangential to a circle of position, centered on the Geographical Position of the celestial object of interest. Looking at Bowditch, there is some fuzziness in the definition of a line of position. "Circular lines of position" are synonymous with "circles of position" and lines of position, it seems, can be circles. But when discussing the St Hilaire method, Bowditch (article 1703 in my 1984 edition) describes the LOP as a straight line drawn to be tangential to the circle of position. In his post [NavList 10683], Peter Hakel finally tells us that... "The LOP's are circles", so now we know where he is coming from and his single parameter to describe a circle of position makes more sense. But since we are talking about LOPs in the context of the St Hilaire method, where LOPs are straight lines, I could not see what John Karl was getting at when he talked about "calculating the LOP directly" and I suspect he, too, was talking about the circle of position, not the LOP as (usually) drawn on a chart. Geoffrey --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList+@fer3.com -~----------~----~----~----~------~----~------~--~---