Why Google Earth and Prime Meridian Don’t Line Up

Prime Meridian in Google EarthOne thing several people have noticed since the Google Earth application was released is that the Prime Meridian (0 degrees in Longitude) does not line up with Greenwich, England like they expect. So, if you go to Greenwich in GE, and turn on lat-lon lines by going to the menu “View->Grid”, you will see the Meridian line is about 100 meters east of the Greenwich observatory (viewable quite clearly in the satellite photo). This is not a mistake on Google’s part. The developers of Google Earth (originally known as Keyhole) chose to support the same coordinate system as that used by GPS technology known as WGS-84 World Geodetic System. Here’s an excellent post by one of the GE developers at the Google Earth Community which explains this in detail.
So, if you go to Greenwich, England with your GPS, it will in fact require you to walk about 100 meters to the east of the observatory before you will reach the GPS prime meridian. And don’t believe anyone who tries to tell you Google is trying to realign the planet.

About Frank Taylor

Frank Taylor started the Google Earth Blog in July, 2005 shortly after Google Earth was released. He worked in 3D graphics for many years and was very impressed with this exciting product. Frank left in 2009 to circumnavigate the earth by sailboat as part of the Tahina Expedition.



Comments

  1. bill mcleod says:

    Your comments about wgs84 and google – and the explanation by Seer, raise questions about using GE for navigation worldwide.
    Using GE as the map and a GPS, my house in Queensland, Australia appears about 50 metres from where it actually is.
    My remedy was to screenshot GE for the area, then calibrate the image using Oziexplorer and a number of known points.
    Using this method, I can now be viewed using GPS(and a recalibrated GE image)to an accuracy of about 2 metres.(on the end of a fishing jetty)
    I wonder how the accuracy of google earth (WGS84)
    appears at different points on the globe – apart from Greenwich.
    Anyone know?
    I had considered that perhaps the hi-res “tiles” for some areas, might not have been calibrated accurately by GE mapmakers.
    “globemakers”

  2. Reminds me of the time I took my GPS to a monument in Ecuador where the equator was surveyed by a European scientific team back in the day.
    So while everyone is shuffling by, checking out the monument and enjoying the day, there was a geeky gringo flipping through all his different datums struggling in vain to get exactly 0 latitude to come up on his Garmin.
    Man, those were good times.

  3. Your comments about wgs84 and google – and the explanation by Seer, raise questions about using GE for navigation worldwide.
    Using GE as the map and a GPS, my house in Queensland, Australia appears about 50 metres from where it actually is.
    My remedy was to screenshot GE for the area, then calibrate the image using Oziexplorer and a number of known points.
    Using this method, I can now be viewed using GPS(and a recalibrated GE image)to an accuracy of about 2 metres.(on the end of a fishing jetty)

  4. I’m using a very handy tool named GoogleOzi http://flygps.host.sk/GoogleOzi to make a ‘screenshot’ of Google Earth. Excelent is that it makes an OziExplorer map file, so it is calibrated already with 1 m accuracy!

  5. Comparing sailor-maps (paper-version) with Gearth, I found for the Dutch coastal waters Gearth grid position inaccuracies of 85 m lon to the east and 90 m lat to the north. Combined a 125 m @45 degrees vector. This inaccuracy seems to be an intentional offset, as it is found at many points in lat/lon.
    Map reference is “Hydrografische kaart 1812, Waddenzee oostblad, submap 1812.3, insert Lauwersoog, position is centre of crossing coastal road and lock, lat 53.408198 and lon 6.196590. Gearth gives lat 53.4091667 and lon 6.1980
    Kind regards,
    Uulke Visser
    Enschede, Netherlands.

  6. I’ve noted some disturbing errors in Trinidad and Tobago – even using the WGS84 protocol with my old trustworthy Garmin12. We’re talking about 50 meters off, as Bill McLeod notes.
    The good news is that Naparima BWI is just as inaccurate.

  7. Could this be anything to do with expanding Earth theory? If you don’t know about it.. google it.. or see it on youube.
    Cheers,
    D

  8. ray brown jr says:

    AS TO INACUARCIES 0F COORDINATES IN VARIOUS PLACES, YOU ARE PROBABLY USING THE WGS84 DATUM INSTEAD OF YOUR LOCAL DATUM WHICH WILL CAUSE AN OFFSET OF ANY NUMBER OF METERS. FOR INSTANCE, THE WGS84 (NAD83) COORDINATES FOR THE SPACE NEEDLE HERE IN SEATTLE ARE 47.6205 -122.349278. THE NAD27 COORDINATES FOR THE SPACE NEEDLE ARE 47.620667 -122.348056. THIS LEADS TO A DIFEERANCE OF 95 METERS OR 312 FEET BETWEEN THE 2 DATUMS. SOME PLACES IN THE WORLD ARE 300 METERS OR MORE DIFFERENT BETWEEN LOCAL AND WGS84 DATUMS. WHEN THEY STARTED LAUNCHING ICBM MISSILES AND INTERCONTINENAL AIR TRAVEL EVERYONE HAD TO BE ON THE SAME PAGE FOR POSITIONAL ACCURACY. LOCAL DATUMS BECAME OBSOLETE UNLESS THOSE DATUMS WERE MADE TO MATCH WGS84. THANKS-RAY BROWN-SEATTLE.

  9. I’ve noticed that Google Earth coordinates are off by more than 80 meters in Eastern MA from WGS84 data. Here the error is to the SSW.

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