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: Position discepancy
    From: Greg Rudzinski
    Date: 2011 Dec 13, 12:10 -0800

    Fred,

    If you are comparing a celestial line of position of Polaris or Jupiter to a GPS position you are doing well to be within 2 nautical miles. Celestial is used when there is plenty of sea room. When in sight of land there is a switch to piloting where positioning will be more precise using bearings, horizontal angles, soundings, and ranges. Bowditch will explain how sight variables will produce uncertainties which in some cases will be over 3 nautical miles even with a perfect observation and no mistakes in sight reduction. Some of the uncertainty variables are time, height of eye, temperature, pressure, index error, and the perpendicularity of the sextant to the horizon.

    Greg Rudzinski

    [NavList] Position discepancy
    From: fredstevens---com
    Date: 13 Dec 2011 10:43

    I have a known location... well, "known" as far as Google
    Earth goes. I am assuming that it is a correct position
    since it is verified by GPS. When I go to either the NA or
    online almanacs, like USNO Almanac or Henning Umland's to
    verify the coordinates using Jupiter and Polaris, there is
    always a significant discrepancy between them and those from
    GPS/GoogleEarth, a few nautical miles at the very least.
    Enough to be worrisome if at sea.

    Any idea why so much difference?

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

       
    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