NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: AP terminology, WAS: 2-Body Fix -- take three
From: Tom Sult
Date: 2009 Nov 13, 14:38 -0600
From: Tom Sult
Date: 2009 Nov 13, 14:38 -0600
Well the summer calculated 3 points based on assumptions also. If you recall the story he calculated his position then made an sumption a few degrees one way then the other to get three point. So in a sence summer is a third redundancy of the St H method. Thomas A. Sult, MD Sent from iPhone On Nov 13, 2009, at 14:33, John Karlwrote: > > No one has addressed my question of why the St Hilaire method > calculates an altitude at a location our ship is NOT at, when we've > just measured the altitude where our ship IS at. (For politically > correct reasons, I'm not using the name of this location.) > > Now lets go back to Sumner's 1837 calculation, where he picked three > different longitudes and calculated three points on the circular LOP. > This calculation is exact, and the equation for each point is the same > as the one of the two necessary in the St Hilaire method (thus each > Sumner point is half the work of a St Hilaire reduction). And he > could calculate as many exact points as he wished. > > So I'll put my question yet another way: Why is the St Hilaire method > superior to Sumner's and consequently the only one used today?? > > I claim that the answer to this question has been made confusing > because of the conventional name (names?) used for the location of the > St Hilaire altitude calculation. As evidence of this confusion I note > that some authors write that we need to assume some point because the > distance between the GP and the LOP is too great to plot, that there's > insufficient information to plot the LOP, or that iterations are > required to get exact points on the LOP. The Sumner calculation > demonstrates that none of this is correct. > > JK > > > > --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList+@fer3.com -~----------~----~----~----~------~----~------~--~---