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
    Name or NavList Code:
    Email:
       
    Reply
    One-body fix
    From: Peter Hakel
    Date: 2009 Apr 26, 11:11 -0700
    Re: [NavList 8049] The rapid-fire fix

    Thank you, Frank, for the detailed discussion of the rapid-fire fix from multiple observations of a single body during a very short time interval.  Coincidentally I have just been looking into the rather academic problem of obtaining a fix from the altitude and azimuth of a body. I understand that this is not done in practice because azimuth is difficult/impossible to measure to sufficient accuracy.  Nevertheless, I would like to know just how accurately one can measure azimuth in the field/ocean and what portable devices (besides compasses), are available for this (if any).

    I hereby display the solutions to this "one-body fix" problem, if only as a curiosity.  I expect that these have been worked out before but I haven't found them anywhere so far (references would be much appreciated).  The known quantities are the GP (Dec, GHA), observed altitude (Ho), and azimuth to GP (Zn).  From the navigation triangle we can calculate the LHA and then the Latitude:

    sin LHA = sin Zn * cos Ho / cos Dec

    sin Latitude = ( sin Ho * sin Dec  -  cos Ho * cos Dec * cos LHA * cos Zn )  /  ( 1  -  cos Ho * cos Dec * sin LHA * sin Zn )

    The denominator in the Latitude expression can vanish under very special circumstances, in which the result is Latitude = 0.  I don't think we need to worry about cos Dec = 0 in the first formula.  The LHA is hereby considered to be between -180 and +180 degrees rather than the conventional 0 - 360 degree range.  An additional step in getting the LHA from the arcsine is needed when Ho < 0, i.e. for bodies below the horizon. In the end, Longitude = - ( GHA + LHA ).


    Peter Hakel



    --~--~---------~--~----~------------~-------~--~----~
    Navigation List archive: www.navlist.net
    To post, email NavList@navlist.net
    To , email NavList-@navlist.net
    -~----------~----~----~----~------~----~------~--~---

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    NavList is a community devoted to the preservation and practice of celestial navigation and other methods of traditional position-finding. We're a group of navigators, navigation enthusiasts and hobbyists, mathematicians and physicists, and historians interested in all aspects of navigation but primarily those techniques which are non-electronic.

    To post a message, if you are already signed up as a NavList member, start a new discussion or reply to any posted message and use your posting code (this is a simple low-security password assigned when you join). You may also join by posting. Your first on-topic messsage automatically makes you a member, and a posting code will be assigned and emailed to you for future posts.

    Uniquely, the NavList message boards also permit full interaction entirely by email. You can optionally receive individual posts or daily digests by email, and any member can post messages by email (bypassing the web site) by sending to our posting address which is "NavList@NavList.net". This functionality is similar to a traditional Internet mailing list: post by email, read by email, reply by email. Most members will prefer the web interface here for posting and replying to messages.

    NavList is more than an online community... more about that another day.

    © Copyright notice: please note that the rights to all messages and posts in this discussion group are held by their respective authors. No messages or text or images extracted from messages may be reproduced without the explicit consent of the message author. Email me, Frank Reed, if you have any questions.

    Join / Get NavList ID Code

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

    A NavList ID Code guarantees your identity in NavList posts and allows faster posting of messages.

    Retrieve a NavList ID Code

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

    Email Settings

    NavList ID 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