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: great circle distance
    From: Roger M. Derby
    Date: 2000 May 23, 1:12 PM

    As you say, it comes from a time before electronic calculators.
    
    When using computers of whatever size you have to take into account the
    assumptions made in programming the math library.  Trig functions are
    especially contankerous beasts; e.g. zero degrees assumed to be East instead
    of North, only one quadrant programmed with the angle converted in a
    non-documented fashion, etc.  Humans look for the reasonable answer.  The
    computer just does as it's told.  I spent many hours making a VAX 11-750 do
    great circle calculations correctly.  It was ornery enough that I finally
    set up a table of test cases to run after each fix, just to ensure that the
    thing hadn't gone awry again.
    
    Roger
    
    ----- Original Message -----
    From  "Zorbec Legras" 
    To: 
    Sent: Tuesday, May 23, 2000 9:40 AM
    Subject: [NAV-L] great circle distance
    
    
    > Van: Frank Dinkelaar 
    > Aan: NAVIGATION-L{at}listserv.webkahuna.com
    > Onderwerp: Re: short horizon Hs correction
    > Datum: din, 23 mei 2000 13:28
    >
    >
    >
    > cos D =  abs(sinL1 - sinL2) - abs(cosL1 x cosL2 x cos Dlo)
    >
    >
    > why abs?
    >
    > look at this it comes from a time there was no Electonic calculators
    >
    > a= (sin l1 X sin l2)
    >  ==> sign of a is + l1 l2 same name / - diff name
    >
    > b= (cos l1 X cos l2 X cos Dlo)
    > ==> sign of b is + if Dlo < 90�/ - if DLO > 90�
    >
    > cos D = a-b
    >
    > D in minutes of angle is the distance in Nm
    >
    >
    > Pm if Dlo > 180� turn the ship!
    >
    >
    >
    > Cpt. Zorbec
    >
    >
    >
    > .
    > ______________________________________________
    > FREE Personalized Email at Mail.com
    > Sign up at http://www.mail.com/?sr=signup
    >
    

       
    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