Welcome to the NavList Message Boards.

NavList:

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

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
       
    Reply
    Re: HO 211 (Ageton) sight reduction accuracy
    From: Paul Hirose
    Date: 2016 Jun 28, 22:57 -0700

    On 2016-06-22 22:03, Paul Hirose wrote:
    > alt   alt   alt   az    az     az
    > RMS   >.5'  max   RMS   >.5°   max     table type
    >
    > 0.69' 4.24% 23.7' 1.71' 0.054% 1.457°  0.2' 84° no interp
    > 0.55' 3.74% 21.1' 1.65' 0.05%  1.445°  0.2' 84° interp t<5
    > 0.55' 3.74% 23.8' 1.62' 0.047% 1.102°  0.2' 84° interp K<8
    >
    > 0.62' 2.96% 19.3' 1.41' 0.034% 0.852°  0.2' 54° no interp
    > 0.28' 1.95% 12.3' 1.30' 0.027% 1.045°  0.2' 54° interp t<5
    > 0.27' 1.52% 12.5' 1.32' 0.027% 1.015°  0.2' 54° interp t<8
    > 0.27' 1.65% 12.0' 1.26' 0.021% 0.787°  0.2' 54° interp K<5
    > 0.28' 1.42% 12.1' 1.30' 0.023% 0.987°  0.2' 54° interp K<8
    >
    > 0.42' 11.5% 14.2' 2.53' 0.16%  1.650°  0.5' 54° interp t<5
    
    I forgot to examine a couple cases in my previous message on a 0.2' table.
    
    If such a table is used with no interpolation and you exclude sights
    where t is within 5° of 90, and also exclude stars with declination
    greater than 75°, root mean square altitude error is 0.17', 1.25% of the
    solutions have more than half a minute error, and the worst is 3.1'.
    
    In addition to the above, suppose the precision of function A changes
    from whole numbers to tenths at 54° instead of 84°, and there's a
    corresponding change to B. Then RMS altitude error decreases to 0.14',
    0.648% exceed 0.5' error, and the worst altitude is 1.7'.
    
    The significance of 54° is that it's the point where the A function no
    longer changes one count per tenth minute difference in angle.
    
    Now consider a hypothetical HO 211 tabulated every tenth minute. With
    600 entries per degree, I don't think it would be practical, but it may
    be interesting to see how such a table performs in a Monte Carlo simulation.
    
    With no interpolation, altitude RMS error is 0.60', 3.24% exceed 0.5'
    and worst altitude is 21.2' off. Moving the change of precision to 54°
    makes a lot of sense at this tabulation interval, since otherwise you
    get many adjacent table entries with the same values.
    
    That improves altitude RMS from 0.60' to 0.36', but there's little
    difference in the worst error. Increasing precision to two decimal
    places at 85° doesn't help much either.
    
    Interpolation of B(R) from A(R) when t is near 90° gets RMS altitude
    error down to a quarter minute. However, the biggest gain occurs if we
    simply exclude t near 90 and high declinations. Then RMS altitude error
    is 0.08' and the worst sight is only 1.1'.
    
    Of course it's not always practical to exclude the 8% of sights that
    meet those criteria. And as I've shown, interpolation when a sight is in
    the danger zone doesn't guarantee accurate results. We need a different
    solution for such sights. One is the Sadler technique, which will be
    evaluated in my next message.
    
    alt   alt   alt   az    az     az
    RMS   >.5'  max   RMS   >.5°   max     table type
    
    0.17' 1.25%  3.1' 1.65' 0.05%  1.362°  .2' 84° no interp t<5 d<75
    0.14' 0.648% 1.7' 1.32' 0.022% 0.882°  .2' 54° no interp t<5 d<75
    
    0.60' 3.24% 21.2' 1.43' 0.037% 1.153°  .1' 84° no interp
    0.36' 1.70% 18.2' 0.85' 0.006% 0.652°  .1' 54° no interp
    0.25' 1.30% 14.4' 0.79' 0.006% 0.773°  .1' 54° interp t<5
    0.38' 1.71% 14.6' 0.86' 0.002% 0.733°  .1' 54°/85 no interp
    0.26' 1.18% 12.4' 0.82' 0.004% 0.808°  .1' 54°/85 interp t>5
    0.08' 0.14%  1.1' 0.85' 0.002% 0.672°  .1' 54° no interp t<5 d<75
    

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

    Name:
    (please, no nicknames or handles)
    Email:
    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:

    Email Settings

    Posting Code:

    Custom Index

    Subject:
    Author:
    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