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
    Trouble solving for spherical triangle
    From: Hahns Burg
    Date: 2020 Jul 11, 16:36 -0700

    I’m interested in spherical trigonometry and have written a very basic BASIC program (see Excel file attached) which calculates destination (lat and lon) for a given DR (lat, lon), course, and distance.  I’ve solved for the spherical triangle (example: Law of Sines and Law of Cosines hold for my solution).

    The Rub

    Here’s the rub:  while the math itself holds, where course is set to exactly east or west (i..e., 90 or 270), I’m noticing destination latitude does not equal original DR latitude (where we know latitude should not be changing).  The errors increase with distance greater than 100 nmi.

    I have a simple Excel spreadsheet modeling the following:

    Three Points:

    A = North Pole

    B = DR

    C = Destination

    Three sides and angles from center of earth

    a = distance sailed

    c = [90 - DR latitude] and distance from North Pole

    b = [90- destination latitude] and distance from North Pole

    My math starts with B.   Then solves for c, then a; and lastly solves for the balance of A and C.    See attached Excel file.

    What am I doing wrong?

     

    File:
    Spherical-Trigonometry.xlsx
       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Get a 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