Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Re: GPS & Magnetic Bearings
    From: Brooke Clarke
    Date: 2003 Feb 9, 15:25 -0800

    Hi Rino
    Yes, there are "attitude sensing" GPS receivers that use multiple antennas, 
    but it's more comples than just using two antennas.
    "GPS-based attitude determination is just an extension of differential carrier 
    phase position determination." quoted from:
    an interesting article.
    Rino wrote:
    > There are some models of GPS receivers that can give you a heading:  They
    > do it by using two antennas, and then calculating the heading between
    > them.
    > Rino
    > -----Original Message-----
    > From: Navigation Mailing List
    > [mailto:NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM]On Behalf Of Robert Eno
    > Sent: Sunday, February 09, 2003 17:11
    > Subject: Re: GPS & Magnetic Bearings
    > Just a quick note on the magnetic variation: I was told by an authority on
    > the subject that after 5 years, the accuracy of the magnetic variation
    > information contained within your GPS software starts to drop off. The
    > reason being, is that the calculations for determining the variation is
    > based on a set rate for a particular epoch. As we all know, the rate of
    > change in variation is generally steady over a short period of time,
    > however, over the long haul, that rate starts to change. So for example,
    > if
    > in 1995, the rate of change for a certain area was 12 minutes eastward per
    > year, that rate of change might be, say 20 minutes eastward per year in
    > 2003.
    > That is my understanding but I could have misinterpreted the message.
    > Comments?
    > Robert Eno
    > ----- Original Message -----
    > From: Brooke Clarke 
    > To: 
    > Sent: Sunday, February 09, 2003 2:39 PM
    > Subject: GPS & Magnetic Bearings
    > > Hi:
    > >
    > > I know my old Motorola GPS uses the World Magnetic Model that is updated
    > every 5 years, mine has the 1995 version.  This model will tell you the
    > magnetic deviation if you know the date and your location, both of which a
    > GPS receiver knows.
    > >
    > > GPS has no provision to determine direction. For example on a trip to
    > Japan I had a way point for my hotel in a big city.  Many blocks away I
    > knew
    > I needed to head in a certain direction to get back, but the GPS has no
    > compass functionality.  The answer was to walk very quickly for a block
    > and
    > then see which direction the GPS said I was going based on the change in
    > my
    > position.  Some GPS receivers now incorporate a fluxgate or other
    > > electronic compass into the receiver for this reason, but the GPS system
    > derives bearing from change in position.  For more on sensors and the WMM
    > see my web page: http://www.pacificsites.com/~brooke/Sensors.shtml#Earth's
    > Magnetic
    > >
    > > Have Fun,
    > >
    > > Brooke
    > >
    > > Jared Sherman wrote:
    > >
    > > > Fred-
    > > >  
    > > >
    > > > GPS knows nothing about steering directions, it only knows the actual
    > course taken by the GPS antenna. If you are steering 340 but making 350
    > due
    > to leeway, the GPS will only tell you that you are making 350. Or, that
    > the
    > GPS antenna is making 350 so it presumes the rest of the boat is moving
    > that
    > way too. GPS literally "can't" be swung like a compass can.
    > > >
    > > > GPS knows nothing about true/magnetic, unless someone tells it to
    > display one versus the other and gives it deviation information. I'm not
    > sure if that is available from the GPS system (I don't think so) but the
    > deviation data for the world can be stored in ROM and then "generated" by
    > the GPS unit running the current date against that to extrapolate the
    > correct information for the time and position that the GPS system has
    > given
    > it.
    > > >
    > > > There was some discussion...here?...some time ago about one brand of
    > GPS
    > that indeed had a firmware error and was apparently calculating
    > magnetic/true incorrectly. French or English I think--a brand that doesn't
    > appear here on the US market.
    > >

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    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 Settings

    Posting Code:

    Custom Index

    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