NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: typical standard deviation?
From: Jeremy C
Date: 2009 Aug 15, 11:55 EDT
From: Jeremy C
Date: 2009 Aug 15, 11:55 EDT
I can provide all sorts of data for people with more of a math bent, but i
am but one observer.
This might be something to try at the bi-annual gathering at Mystic with
lunar distance measurements. A number of observers with the same sextant
taking say 10 observations or so each should be able to come up with some decent
data to begin with.
Sadly at sea, the only place you will get a fairly large number of
observers with sextants is a school ship with the cadet cadre doing their sea
projects. The big problem with this is that they really don't care enough
for the most part to try and get accurate sights and are also neophytes so will
be all over the place with their observations. Still, if I ever go out on
a training ships as an instructor, i might look at gathering data of that nature
for whatever it's worth.
Jeremy
In a message dated 8/14/2009 6:17:26 A.M. Central Asia Standard Time,
maartenvannoorden@gmail.com writes:
>EXCELLENT! I am afraid that with so few people such as myself out here
who actually practice celnav, our hopes for at sea data are fairly
slim,
especially from the larger vessels.
>I wouldn't expect to find such data. During the history of celestial
navigation _IT_ was the most accurate navigation system available so
there was no other data that the celnav positions could have been
compared with to develop such an accuracy data set. Really, only since
the development of GPS (maybe LORAN C) has such another set of
positions
become available so only now can such data be developed. But how many
navigators continued to use celnav on a regular basis and then logged
the accuracy of the celnav position derived after comparison with the
contemporary GPS positions and then made their logs available.
Acually you don't need an exact GPS nor a hugh amount of people to
estimate the error. A good way of doing the analysis would be to use
what is called a 'MSA' (Measurement System Analysis) and is used in
industry to distinguish between operator errors and machine errors. A
simple setup would involve one sextant, one ship and 2 or 3 operators.
The operators (users) will shoot in random orders with the same
instrument and calculate their position. The total variance (square of
the standard deviation) is the sum of the variance of the inter
operator error and the error caused by the measurement setup.
If you want to include all types of potential errors due to for
instance horizon (as mentioned above), you can either instruct the
operators very well (the error will be in the test setup) or not at
all (the error will be in the operator part).
If the experiment is carried out at the same location, no GPS fix is
needed or desired, it will add an extra variance to the equation (but
probably very small)
If somebody is willing to carry out this experiment, I am more than
happy to assist with the statistical part.
Regards,
Maarten van Noorden
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