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: Question about Pub 249 combined Star and Planet sight reduction
    From: Rod Deyo
    Date: 2000 Nov 20, 8:36 PM

    My thanks to Richard B. Emerson, Dan Allen, and Paul Hirose for their
    responses. A few further comments:
    
    1) Perhaps the issue is moot for small craft when the measured Hs values are
    uncertain, but as you get away from the epoch used for Pub 249 Vol 1
    calculations, the nutation and procession corrections are as large as 4 nm .
    I hate to just give away that amount of error on what otherwise might be
    consistent sights.
    2) The question I raised was how to properly weight multiple LOPs when some
    of them are intended to be corrected as a single group. Just eyeballing the
    answer is tough for me if there are five LOPs, three which need to be moved
    a few miles in a particular direction (for example, several Pub. 249 Vol 1
    star sights corrected for nutation and procession) and then weighted against
    two that are not shifted (several planet or other star sights not done using
    Pub 249 Vol 1, but using the Almanac and 249 Vols 2-3 or Pub 229). Ideally,
    you then pick the point as your final fix that minimizes the square of the
    distance from each of the corrected LOPs (this is an unbiased estimate,
    since no line or set of  lines is favored over the others).
    3) At the moment, I've convinced myself that it's probably best to either a)
    assume it makes no real difference and do not correct (this is probably good
    enough if the correction is 1 nm or less) or b) correct each AP by the
    nutation and procession, plot the resulting LOPs, and then eyeball each of
    the LOPs together to get the final fix.
    
    Rod Deyo
    

       
    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