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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Clarification offered and requested Re: Multi-Moon line exercise in 2 parts
From: UNK
Date: 2009 Aug 9, 14:07 -0700
From: UNK
Date: 2009 Aug 9, 14:07 -0700
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 ********************** ------------------------------------------------------------- [Sent from archive by: antoine.m.couette-AT-club-internet.fr] --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---