NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Celnav article in Ocean Navigator Magazine
From: Stan K
Date: 2016 May 11, 04:10 -0400
From: Stan K
Date: 2016 May 11, 04:10 -0400
The Sight Averaging tool of Celestial Tools (V5.1.1 or later) has the option of doing a least-squares linear regression fit of the entered sights (time and altitude). It then calculates the "residuals" for each sight, the differences, in arc-minutes between the measured altitude entered and the altitude calculated by the least-squares linear regression fit determined from using all the entered times and altitudes. The user can then eliminate the outlier sights, the ones with large residuals, from the average, or, as Robert suggested, just reduce the one sight with the smallest residual.
-----Original Message-----
From: Robert VanderPol II <NoReply_RobertVanderPolII@fer3.com>
To: slk1000 <slk1000@aol.com>
Sent: Wed, May 11, 2016 2:19 am
Subject: [NavList] Re: Celnav article in Ocean Navigator Magazine
While the ON article is correct that the median is a statistically more valid value, it is also not computationally efficient. The ON method described only works well if you are using electronics for the sight reduction. If I were doing it manually, the only way I would use that method is if it involved a critical landfall with obscured hazards offshore and/or I had a lot of time to kill. Actually, for manual reduction there is a subset of celestial measurements that the median would work for, specifically those that involve the altitude being at a constant or almost constant height: the noon shot, polaris or any body that is approaching meridian passage. Pick the median altitude and associated time then reduce just the one data point. Other than the average there is a graphical method I think would work generally. Graph the data points, eyeball a line to fit the data, then pick the one closest to the line and reduce that. All in all I think I will stick with averaging 3 to 5 sights.
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From: Robert VanderPol II <NoReply_RobertVanderPolII@fer3.com>
To: slk1000 <slk1000@aol.com>
Sent: Wed, May 11, 2016 2:19 am
Subject: [NavList] Re: Celnav article in Ocean Navigator Magazine
While the ON article is correct that the median is a statistically more valid value, it is also not computationally efficient. The ON method described only works well if you are using electronics for the sight reduction. If I were doing it manually, the only way I would use that method is if it involved a critical landfall with obscured hazards offshore and/or I had a lot of time to kill. Actually, for manual reduction there is a subset of celestial measurements that the median would work for, specifically those that involve the altitude being at a constant or almost constant height: the noon shot, polaris or any body that is approaching meridian passage. Pick the median altitude and associated time then reduce just the one data point. Other than the average there is a graphical method I think would work generally. Graph the data points, eyeball a line to fit the data, then pick the one closest to the line and reduce that. All in all I think I will stick with averaging 3 to 5 sights.
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