NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Accuracy of sextant observations at sea
From: Gary LaPook
Date: 2010 Sep 23, 13:24 -0700
From: Gary LaPook
Date: 2010 Sep 23, 13:24 -0700
Well, I had been feeling pretty good about my observations until I
read Jeremy's post. But, of course, he IS a professional....
gl
On 9/23/2010 11:56 AM, Anabasis75@aol.com wrote:
gl
On 9/23/2010 11:56 AM, Anabasis75@aol.com wrote:
Hi Gary,I'll quote myself here [NavList 9887]:On Sep 23, 2009 3:40 pm, Anabasi...---com wrote:
> I shot 70 star fixes on my trip from Japan to the USA and here are a few
> interesting statistics.
>
> 1) average fix error from GPS: 0.566 nm (low of 0.0 and high of 2.7 nm
> error)
>
> 2) 88.6% of the fixes were under 1.0 nm fix error.
>
> 3) 60.0% of the fixes were under 0.5 nm fix error
>
> 4) two fixes had errors under 0.05 nm (under 100 meters).
>
> My next project is to determine the average intercept based on the GPS fix
> as the DR but that is over 700 data points so might be awhile.
>
> Jeremy
As you can see, these are position errors, not LOP errors. I also ran standard Dev for my fixes and it was 0.5813 nm. I will add that my worst fix was 2.7 nm off under awful conditions.The trouble I have with LOP statistics is that there are so many variables at play as render them only interesting but not very useful. With a good sky and horizon I can pinwheel every time (intercepts well under 1 nm), if the horizon and/or sky is terrible, I can have errors of several miles. Also, can someone expect the aforementioned statistics in a bouncing sailboat as opposed to a large ship? Probably not.I just ran the statistics for the individual LOPs, 551 in all. These were shot in a wide variety of conditions including the haze of the East China Sea, near Cape Hope, and in the tropics. There is a wide variation of error from day to day and twilight to twilight depending on the environment.I only ran them on the computer reduced sights as these use GPS fixes for the AP as opposed to my tabular reductions. (planets, the moon, and stars) I didn't use the computer for most of my sunlines, but there are a few included in there.Standard deviation for all 551 sights was .800225.I did shoot 1 moonlight fix. The position error was about 2.5 nm which would be good enough in a pinch, but well below my standard.Jeremy