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Aug 09, 2009


Dear ALL, and especially dear Jeremy and Peter,




... A bit surprised here and there by some of your comments, I came to the 
conclusion that I had missed some important data as earlier submitted by you 
Jeremy.

And that is true ... I have based all my computations and results on 
exclusively the 33 shots performed within the time frame UT 9:39:40 - UT 
10:01:35 as detailed in the "Moon near LAM" file.

So, I had not noticed - until a few minutes ago - the file "Moon Away from LAM"... 

     **** which explains why I could not understand some comments about an 
observation totally outside the time frame indicated hereabove, which 
apparently is considered a "faulty one " for some reason. I did not process 
such observation which is in the file "Moon away from LAN" which I have not 
studied until now.

      ***** This also explains why I was surprised at Peter's comments about 
processing "all 30" shots, while I did process "33 shots" ... simply because 
Peter was referring to this "Moon away from LAN" file which does have 30 
shots while the file "Moon Near LAM" carries 33 shots,
      
      ***** It also explains why Peter is wondering why we have so different 
SDEV in Longitude ( you have over 40 ' while I have 3.8 ' ) ... simply 
because we do not speak about the same set of measures.

---------

So, thank you Jeremy for your reply and results. Before I could comment in 
detail about what seems significant differences between your GPS values, 
Peter's results and mine, I would first notice the following.

First

Jeremy you indicate that, out of the 33 shots you have posted, you processed 
only 20. In order to have all results compared on the same basis, would you 
be so kind as to indicate which exact 20 shots you processed so that I can 
re-run my computations on your exact same set of values.

Second,

Peter please be so kind as to confirm that you did process all the 33 shots of 
the "Moon near LAN" file, and only these ones.

Last but not least :

     **** for those of us who use a "parabolic fitting" type of software, I 
would surmise that your software first identifies culmination time and 
height, from the curve shape, and then computes LAM as well as associated 
Height at time of LAM. Please be so kind as to indicate time elapsed in 
seconds between Culmination Time and LAM time. I get 2.9 seconds for this 
result.

     ***** when running Marcq Saint Hilaire method on 33 running fixes using 
Oberved position at LAM as DR position, I am getting back exactly to the same 
result within 0.1 NM (while giving all 33 observations exactly the same 
weight ). I would therefore think that, all your 33 data having been 
processed by 2 entirely different mathematical approach, this would somewhat 
reduce the risk of error since in both cases I get the same results.

So I would offer also that you rerun all 33 sights from your time of Transit + 
your position at Transit and confirm that your final result exactly matches 
your position found through a "parabolic apporach method". If such is the 
case, then we have a very interesting case to study since all three of us 
would get exactly the same own results through 2 different methods, with the 
only BIG problem being that our various results would not currently seem to 
match. WE would therefore need to dig further and I will offer all intercepts 
and azimut values recomputed from any of your LAM posiiton and time used as a 
basis for running fixes.

Hopefully I am clear enough on this topic ...

I might be late to reply to your answers since I am flying again in a few 
days, but I will certainly follow up on this subject.


Best Regards to you all

Antoine


Antoine M. Cou?tte


PS : George, thank you very much for your extremely kind word of "welcome 
aboard " . Well ... I have to confess the following : before being an Airline 
Pilot, I was an Aircraft Carrier Jet A/C Pilot ( French Navy and US Navy ), 
and before being an Aircraft Carrier Pilot, I was a Naval Officer on a 
destroyer for a number of years in many areas on our Planet, and at a time 
when ONLY Celestial Navigation was available.

***************************[NavList 9440] Re: Multi-Moon line exercise in 2 parts
From: pmh099---com
Date: 9 Aug 2009 09:09

Jeremy,

I ran your on-transit data through my rapid-fire fix program (see attached 
input data file) and obtained results that agree very well with those from my 
earlier posting (calculated by a least-squares parabolic fit).  This way I 
obtain:

1900L fix:
Latitude:     N    21 degrees  47.3'   :  standard deviation =   1.6'
Longitude:  E  130  degrees  04.5'  :  standard deviation = 44.6'

From looking at the azimuths (recorded to 0.1 degrees) the meridian crossing 
(viewed by the observer) occurred at UT=9:51:19.  The moon azimuth was 
changing at the rate of 0.1 degrees per 14 seconds, so this could serve as a 
rough error estimate, say +/- 7s.  Most likely this could be refined by 
taking more data points around LAM and do some kind of fitting and/or 
interpolation.

My standard deviation in longitude is much larger than Antoine's so his 
procedure must be performing a more sophisticated statistical analysis than 
my simple program does.  Perhaps I am overestimating it, considering that my 
mean longitude value is very close to Antoine's.  There may be a rigorous way 
of narrowing its variance down, instead of just using the standard formula. 
On the other hand, my "sigma" values are consistent with the notion that 
meridian transits are good for calculating latitude and less good for 
measuring longitude.  I remember Frank mentioning in the past the notion of 
the "error ellipse" where you would have a smaller error along the azimuth 
line and a larger one along the direction perpendicular to it.  Something to 
think about, perhaps other list members can help me better understand this 
point and resolve the apparent contradiction.

Also, while in this case I do not see any outliers in the data (all intercepts 
are TOWARD and generally increasing with time), there is a curious jump in 
value from 7.5 at 9:48:15, to 9.3 at 9:48:51.  I wonder what happened there, 
although it may be nothing important.


Peter Hakel

**********************
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[Sent from archive by: antoine.m.couette-AT-club-internet.fr]


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