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Thread: Old Garmin calibration?

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    Default Old Garmin calibration?

    Hello,

    I have an old Garmin GPS II +.

    It is about 200 - 400 m out when plotted on a map.

    Is there anyway to calibrate this?

    Thanks

    porkop
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    Wink Garmin Data Base.

    Quote Originally Posted by porkop View Post
    Hello,

    I have an old Garmin GPS II +.

    It is about 200 - 400 m out when plotted on a map.

    Is there anyway to calibrate this?

    Thanks

    porkop
    G'Day Cobber,
    Just going from memory.
    In the setup menu, you can select various data bases.
    They were sold on the world geodetic datum, but to co-ordinate with our maps, you need to select the 1966 Australian Data Base.
    If you've lost the manual, I'm sure that mine is here somewhere, and I'll dig it up if necessary.
    Kindest Regards, " The Druid ".

    Last edited by beer4life; 14-04-10 at 08:04 PM.

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    Talking

    This is the list of the various country Data bases you can use.
    The one you need is on the left page marked with *



    Will post the relevant how to if necessary.
    Last edited by beer4life; 14-04-10 at 09:07 PM.

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    Default

    Thanks B4L, I checked the setting and it was on Austrln Geod 84. I set it to 66 and will check it out with my tomtom coordinates tomorrow.

    Regards

    Porkop
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    Cool

    Quote Originally Posted by porkop View Post
    Thanks B4L, I checked the setting and it was on Austrln Geod 84. I set it to 66 and will check it out with my tomtom coordinates tomorrow.

    Regards

    Porkop
    G'Day Cobber,
    First went down this road about 1993 to sort out the location of Holbrook Airport. Later with the location of Shannons Flat Homestead.
    Needless to say, I was able to locate various weed sites and rabbit warrens to within a 5M radius once the US removed their degradation during Desert Storm.
    Surveyors can now, with terrestrial nodes, get down to the mm range.
    Kindest Regards, " The Druid ".

    Last edited by beer4life; 14-04-10 at 09:59 PM.

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    Default

    I have compared it to my tomtom and founf that the garmin is out by

    Latitude .09 minute
    Longitude .07 minute

    how does this compare to actual metres on the ground??

    porkop
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    Wink GPS and Map Datum co-ordinates.

    Quote Originally Posted by porkop View Post
    I have compared it to my tomtom and founf that the garmin is out by

    Latitude .09 minute
    Longitude .07 minute

    how does this compare to actual metres on the ground??

    porkop

    G'Day Cobber,
    That's like comparing chalk with cheese.
    Do you know what datum the Tomtom is using?
    I'd be more inclined to say that the Garmin is more accurate when using the correct Datum for the map in use.
    The level of accuracy is reliant on the number of Satellites acquired.
    Wikipedia says, "The internal coordinate system of Google Earth is geographic coordinates (latitude/longitude) on the World Geodetic System of 1984 (WGS84) datum."

    To the best of my knowledge all current Australian topographical maps are on the Australian 1966 Datum.

    1 minute of Latitude is constant at ~ 1.85 Km.
    1 minute of Longitude varies with Latitude from Zero at the Poles to 1.86 Km at the Equator.
    For 40 degrees N or S, 1 minute of longitude ~ 1.42 Km.

    Kindest Regards, " The Druid ".

    Last edited by beer4life; 15-04-10 at 05:33 PM. Reason: Degrees/minutes. oops.

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    Default

    Quote Originally Posted by beer4life View Post

    G'Day Cobber,
    That's like comparing chalk with cheese.
    Do you know what datum the Tomtom is using?
    I'd be more inclined to say that the Garmin is more accurate when using the correct Datum for the map in use.
    The level of accuracy is reliant on the number of Satellites acquired.

    To the best of my knowledge all current Australian topographical maps are on the Australian 1966 Datum.

    1 minute of Latitude is constant at ~ 1.85 Km.
    1 minute of Longitude varies with Latitude from Zero at the Poles to 1.86 Km at the Equator.
    For 40 degrees N or S, 1 minute of longitude ~ 1.42 Km.

    Kindest Regards, " The Druid ".

    so going by those figures that gives me about an error of

    1850m x .09 = 166.5m Latitude

    and

    1420m x .07 = 99.4m Longitude (average)

    mmmhh well out of calibration.

    Which would seem right when I plotted it on google mapes the other night.



    I am currently using Austrn Geod 66 from the menu list.

    porkop
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    Talking There is no such thing as calibration error!

    Quote Originally Posted by porkop View Post
    so going by those figures that gives me about an error of
    1850m x .09 = 166.5m Latitude
    and
    1420m x .07 = 99.4m Longitude (average)
    mmmhh well out of calibration.
    Which would seem right when I plotted it on google mapes the other night.
    I am currently using Austrn Geod 66 from the menu list.
    porkop
    You've missed the point.
    To compare one with the other, They must both be on the same co-ordinate Datum system.

    All you are doing at the moment is posting the difference in the two datum co-ordinates, and not any errors in one or the other.

    There was such a thing as "Selective Availability" which was turned off during the Gulf War, due to the shortage of Military Units for their front line troops.
    They have undertaken not to turn this back on globally, but now have the capability to use it in a conflict area or wherever.

    Kindest Regards, " The Druid ".

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    Quote Originally Posted by beer4life View Post
    You've missed the point.
    To compare one with the other, They must both be on the same co-ordinate Datum system.

    All you are doing at the moment is posting the difference in the two datum co-ordinates, and not any errors in one or the other.

    There was such a thing as "Selective Availability" which was turned off during the Gulf War, due to the shortage of Military Units for their front line troops.
    They have undertaken not to turn this back on globally, but now have the capability to use it in a conflict area or wherever.

    Kindest Regards, " The Druid ".


    Ok, how do I tell what datum my tomtom is in. the old garmin is easy, it has many to choose from but he tomtom just comes up with maps.
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    Talking

    Quote Originally Posted by porkop View Post
    Ok, how do I tell what datum my tomtom is in. the old garmin is easy, it has many to choose from but he tomtom just comes up with maps.
    OK, to spell it out, your Tomtom is fine for street navigation, dare I say quite accurate when applied to google earth maps which use the Word '84 Geodetic Datum.
    If you apply those co-ordinates to a Central Mapping Authority Topographical Map, based on the 1966 Australian datum, you will be in error as you have noted.
    If you set the Garmin to the WGD84, it should very closely agree with the TomTom for your current location.

    To repeat, you do not calibrate a GPS unit, the co-ordinates are obtained from an algorithm with measured time from several Satellites with extremely accurate on board Atomic Clocks.

    In a nutshell, Surveyors do not use TomToms, they're for the yokels.

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    Quote Originally Posted by beer4life View Post
    In a nutshell, Surveyors do not use TomToms, they're for the yokels.
    Have you ever tried using a theodolite while navigation back streets at night?
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    I have changed the garmins datum to Australian Gead 84 and now I have a 4 sec error when comparing to the tomtom, this equates to about 3m error between the 2.

    I can live with that.

    Thanks for your assistance.
    __________________________________________________ __
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    Wink

    Quote Originally Posted by porkop View Post
    I have changed the garmins datum to Australian Gead 84 and now I have a 4 sec error when comparing to the tomtom, this equates to about 3m error between the 2.

    I can live with that.

    Thanks for your assistance.
    Well, it is within spittin' distance. But don't forget you'll be way out on our Topographic maps.



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