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: Cocked hats, again.
    From: Peter Fogg
    Date: 2007 Mar 17, 07:05 +1100


    DW: "An attemp to summarize and establish consensus."
    1. The most likely location is the center of the cocked hat.
    2. The probability of being within the cocked hat is 25%.

    DW; one statement contradicts the other! The thing about the centre is not that it is the most likely location, it is this:
    It is the ONLY fix position that can be calculated.

    Let's say that you are terribly worried that your shape might not enclose the position (why, I'm not sure, although this assumption underlies this subject). So you decide to enlarge the shape by an equal amount applied to each position line, equal to one standard deviation. Now you have a larger triangle, and are assured that it contains the position by an increase of about 70%.

    Let's say you're still worried (oh yes, you're a determined worrier). So you increase the size of your shape by another same amount. Now you have an even bigger shape, and the assurance that, on average, 90% of the time this much larger shape contains the position.

    Phew! That's a relief. Now you can relax.

    Having relaxed, you then need to put all this work to some useful purpose. Oh yes, that's right, while all this worrying was going on the boat was proceeding on its merry way. You now need to run that (increasingly) old fix forward to establish what you REALLY want to know: where you are! and establish a DR that you can use for your next round of sights.

    And where is that fix?

    Why, its at the centre of all three of these increasingly large shapes that you have constructed, of increasingly larger dimensions! It has remained in exactly the same place!

    At this point you may (or may not) wonder why you went to the effort, since it has changed nothing in terms of your practical navigation.



    --~--~---------~--~----~------------~-------~--~----~
    To post to this group, send email to NavList@fer3.com
    To unsubscribe, send email to NavList-unsubscribe@fer3.com
    -~----------~----~----~----~------~----~------~--~---

       
    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