NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re Obtain a fix when you don't have an clear AP.
From: John Brown
Date: 2015 Jan 16, 15:04 +1030
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From: John Brown
Date: 2015 Jan 16, 15:04 +1030
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I have been following the discussions on this topic with interest and find that most of it revolves around which is the best result using complicated computer programs. I decided to give it a try using the LHA formula method of Sumner and the non mathematical method of Ure which in essence is Sumner's method taken to one more level.
Cos LHA = sin Ho + ( sin Lat x sin Dec ) / ( Cos Lat x Cos Dec ).
The video clip gives a couple of clues to location. The man speaks with an American accent and in the first few minutes he is seen with an American flag waving over his right shoulder. If we assume that his AP is the whole of the United States then we will need a pair of chosen latitudes in Mexico and Canada. From a map in an atlas I decided on Lat 30 N for Mexico and 50 N for Canada.
The first iteration using these chosen latitudes gave a calculated latitude of 46 deg 06 min N.
The second iteration used chosen latitudes of 43 N and 49 N. This gave a calculated latitude of 47 deg 15.9 mins N.
The third and final iteration used chosen latitudes of 46 deg 30 min N and 47 deg 30 min N and yielded a position of Lat 47 deg 28.8 mins N 122 deg 13.9 W. This seems to agree fairly closely with what others have found.
The final position was worked out using Charles Ure's "Mathematical non plotting system." This is contained in a small book that Ure published privately in the mid seventies here in Australia. It came out at the same time that pocket calculators were coming onto the market but he was not an advocate for scientific calculators believing it was too easy to make errors with them. He advised that the simplest calculator was the best and he included in his book sin and cos tables to five decimal places. His book would probably be the smallest book on navigation with the longest title. (see photo.)
Regards,
(the other)
John Brown
Adelaide, South Australia.
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