NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Systematic error and its resolution
From: Frank Reed CT
Date: 2007 Apr 6, 22:50 EDT
See what's free at AOL.com.
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From: Frank Reed CT
Date: 2007 Apr 6, 22:50 EDT
George H, you wrote:
"Take "using corrections with the wrong sign". Well, if you applied the
refraction correction with the wrong sign, it wouldn't make much difference
for high-altitude objects, but would systematically put lower bodies into
the wrong place."
refraction correction with the wrong sign, it wouldn't make much difference
for high-altitude objects, but would systematically put lower bodies into
the wrong place."
Sure. Obviously it can only work with those altitude corrections that have
the same value for all sights. And those are index correction and dip (and
semi-diameter, too, if you're doing a running fix with Sun sights). But
here's an interesting way you could use the graphical method Peter has posted.
You're quite correct, of course, that we don't ordinarily know that there is a
systematic error, and there's no way with just three sights to disentangle
random errors from systematic errors. But suppose we intentionally have a
systematic error. Imagine this; I take altitudes of three stars, and I correct
them for refraction. Now I simply ignore IC and dip and plot LOPs. Why
would I do this? I'm sure I could invent some hypothetical scenario where it
might be necessary in a "practical" case, but let's just say I'm leaving out the
corrections because I'm lazy today and I want to save myself the effort of
doing six additions/subtractions. Instead, I plot my triangle
and do the graphical trick. I've traded six additions and/or subtractions
for some plotting to achieve practically the same result. If nothing else, it's
a neat alternative.
-FER
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
See what's free at AOL.com.
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