Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Re: Clarification offered and requested Re: Multi-Moon line exercise in 2 parts
    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 
    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.
    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.
    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 
         ***** 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 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
    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 
    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 
    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 unsubscribe, email NavList-unsubscribe@fer3.com

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.

    Email Settings

    Posting Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site