NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: The term AP
From: Peter Hakel
Date: 2015 Jan 21, 01:44 +0000
From: Gary LaPook <NoReply_LaPook@fer3.com>
To: pmh099@yahoo.com
Sent: Tuesday, January 20, 2015 4:36 PM
Subject: [NavList] Re: The term AP
From: John Karl <NoReply_JohnKarl@fer3.com>
To: garylapook---.net
Sent: Tuesday, January 20, 2015 9:36 AM
Subject: [NavList] Re: The term AP
From: Peter Hakel
Date: 2015 Jan 21, 01:44 +0000
When I first began learning about CelNav I found the term unhelpful. For a while I thought that the intercept method was about correcting the error introduced by the assumption. Only later I concluded that the AP can be seen as the origin of a convenient local coordinate system accessed via polar coordinates: intercept distance as radius and azimuth as angle.
Peter Hakel
From: Gary LaPook <NoReply_LaPook@fer3.com>
To: pmh099@yahoo.com
Sent: Tuesday, January 20, 2015 4:36 PM
Subject: [NavList] Re: The term AP
"Assuming, just for ease of computation, I were here.." You are assuming that position just for that purpose, obviously nobody believes he is actually there. Why get so upset about the "AP" terminology? Have you ever met anyone who was confused by that concept and label?
gl
From: John Karl <NoReply_JohnKarl@fer3.com>
To: garylapook---.net
Sent: Tuesday, January 20, 2015 9:36 AM
Subject: [NavList] Re: The term AP
Doug &
all,
I don't like the term "trial position" for the same reason I don't like "assumed position." In the St. Hilaire sight reduction we are not trying, experimenting, or assuming anything. Knowing the body's GP and Ho we can compute the entire exact circular LOP. St. Hilaire gives us the azumuth, and great circle distance, to the nearest point (a PLOP) from the AP to the LOP. Knowing this azimuth, we can appoximate the LOP (at the PLOP) with a straight line perpendicular to the intercept. It's the most efficient method of extracting, from only two equations, a very useful approximation to the LOP.
J. Karl
