NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Guy Schwartz
Date: 2009 Mar 7, 21:42 -0800
Lu
When I first learned Celestial Navigation (US sailing) we used
HO 249. I then learned law of cosines which greatly improved (decreased
distances) the GPS or DR location relative to the fix location.
So I guess I do expect law of cosine to be more accurate than HO
249, NASR. There is no rounding to whole numbers with any intermediate factors
using the Law of cosine.
Guy
From: NavList@fer3.com
[mailto:NavList@fer3.com] On Behalf Of Lu Abel
Sent: Saturday, March 07, 2009 8:37 PM
To: NavList@fer3.com
Subject: [NavList 7586] Re: Say it aint so......
Guy:
While I studied for the USPS Navigator grade back when Ageton rather than NASR
was the accepted "compact table" reduction method, I do not believe
the use of an Assumed Position rather than a DR as the starting point for sight
reduction should significantly affect the accuracy of a sight
reduction. The major items affecting the accuracy of a sight
reduction (and remember, this is for calculating Hc and comparing it to Ho) is
the accuracy of almanac data and the granularity of the tabular reduction data.
For a quick sanity check, consider what would happen if you were doing Law of
Cosines with your DR position the same as the assumed L/Lo positions required
by NASR. Would you expect one to be more accurate than the other?
Lu Abel
Guy Schwartz wrote:
Hello folks:
I am studying for the Navigator grade in the US Power Squadron.
Part of my sight folder is a two object sight that need to be
plotted using law of cosine and using the Nautical Almanac Sight Reduction
methods.
The power squadron has a 3 mile tolerance (GPS location vs. fix
position).
My concern is that the 3 mile tolerance is for both Law of
cosine and NASR methods.
It seems to me the NASR would deserve a larger tolerance in that
there are assumed L and Lo positions as starting points
Am I right?
Thank you,
Guy
"May the SCHWARTZ BE WITH YOU"
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