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: Averaging
    From: Peter Fogg
    Date: 2004 Oct 20, 08:58 +1000

    Just a couple of short notes about the simple pen and paper method of comparing a number of sights of the
    same body over a few minutes with a line approximating the apparent rise or 
    fall of the body, caused by the
    rotation of the earth:
    This rise or fall is not a straight line, but an arc. This is why the straight 
    'line of best fit' should not be extended
    beyond 5 minutes.
    The statistical approach, presumably that of simple linear regression, works 
    from the opposite direction. A
    sample of observations is taken and a process employed that best fits a line 
    to them. What I am proposing is
    taking the given line of slope (a function of latitude and azimuth of body 
    observed) and best fitting the obs to it.
    Quite a difference.
    If this process has flaws in extreme situations (and I have wondered, idly, 
    what might happen at the prime
    vertical) then I am indebted for that information, but it doesn't change 
    things for all the other occasions.
    Properly speaking it is not a system of averaging at all. It is a system of 
    choosing, purely by visual comparison,
    a line of best fit. I guess this is why it quite acceptable, indeed necessary, 
    to ignore extreme values. To put it
    most simply, the given line is the fact, the observed values have to 'best 
    fit' it. Not the other way around.

    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