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: Graphical method by Favet / de 'Lisle
    From: Gary LaPook
    Date: 2011 Apr 29, 11:12 -0700

    I am attaching an explanation of how to use the Rust table to determine azimuth.


    EXPLANATION OF AZIMUTH RULES

    In most situations there is no ambiguity as to which
    quarter the Zn lies since you know the approximate direction you are
    looking when you take the sight. The problem arises because the azimuth
    angle is limited to the range of zero to 90 degrees and when the Zn is near
    east or west the correct Zn might fall either
    side of the line so there is an ambiguity in converting from azimuth
    angle to Zn.

    One easy rule to apply first is that if the declination is greater than
    the latitude then the azimuth can never be in the opposite semicircle.
    To generalize this rule, if the declination has
    the same name as the latitude and the declination is greater than the
    latitude, then you start with the direction of the elevated pole (the
    nearer pole) when converting from azimuth angle to azimuth (Zn.)

    The second rule to apply is that if the declination is contrary then the Zn
    must be in the opposite semicircle. To generalize this rule, if the
    declination and the latitude have contrary names then you start with the
    direction of the depressed pole (the further pole) when converting from
    azimuth angle to Zn.

    These two rules take care of most of the cases, especially for
    navigators in low latitudes.

    The remaining ambiguity concerns situations in which the declination is
    the same name as the latitude but is less than the latitude. In this
    situation the azimuth of the body will be both north and south of the
    east - west line during part of each day. In this case use the
    auxiliary table to resolve this remaining ambiguity.

    -----------------------------------------------------------------------

    You can also make a flat Bygrave to compute Hc and Zn or use the Bygrave formulas
    on a calculator. All the information for making a flat Bygrave are here:

    https://sites.google.com/site/fredienoonan/other-flight-navigation-information/modern-bygrave-slide-rule

    gl

    --- On Fri, 4/29/11, Gary LaPook <glapook---.net> wrote:


    From: Gary LaPook <glapook---.net>
    Subject: [NavList] Re: Graphical method by Favet / de 'Lisle
    To: NavList@fer3.com
    Date: Friday, April 29, 2011, 9:20 AM

    On Oct 8, 1:42 pm, Gary LaPook < glap...---net> wrote:
    > Gary LaPook writes:
    >
    > Attached is Rust's diagram for computing the azimuth of the sight which
    > was included in Weems "Line Of Position Book," 1927. It was developed
    > using the sine formula. You enter on the left with LHA and go to the
    > right to the declination then straight up to the altitude then to the
    > right to the azimuth. Also included is a table used to determine in
    > which quadrant the azimuth falls when the body is close to east or west.
    > This diagram can be used with any set of tables, H.O. 208, H.O. 211,
    > etc., and the extra steps used in those tables to compute the azimuth
    > can be disregarded.
    >
    > The shape of these curves show the potential loss of accuracy using the
    > sine formula as the azimuth approaches 90º as the altitude curves become
    > almost vertical and only slight changes in altitude results in large
    > azimuth changes.
    > --
    >
    > Rust diagram.pdf
    > 206KDownload
    ----------------------------------------------------------------
    NavList message boards and member settings: www.fer3.com/NavList
    Members may optionally receive posts by email.
    To cancel email delivery, send a message to NoMail[at]fer3.com
    ----------------------------------------------------------------
    NavList message boards and member settings: www.fer3.com/NavList
    Members may optionally receive posts by email.
    To cancel email delivery, send a message to NoMail[at]fer3.com
    ----------------------------------------------------------------

    File:

      

       
    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