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Thread: Google Earth

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    Silver Lounger t8ntlikly's Avatar
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    I have noticed lately that Google Earth is off about 3 blocks or more. Is anyone else noticed this or maybe I have something askew?
    Attached Images Attached Images
    Thanks John
    Teamwork is essential; it gives the enemy other people to shoot at. (Murphy's War Laws #39)

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    Plutonium Lounger
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    It has always been that way, as far as I know.

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    Silver Lounger t8ntlikly's Avatar
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    [quote name='HansV' post='772041' date='23-Apr-2009 14:05']It has always been that way, as far as I know.[/quote]
    Makes me wish that Virtual Earth had a ruler
    Thanks John
    Teamwork is essential; it gives the enemy other people to shoot at. (Murphy's War Laws #39)

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    Platinum Lounger
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    There are various reasons for this which can cause issues. As you probably know, I am an avid ultrarunner and therefore use GPS mapping tools and hardware to map my routes, speed and distance. When uploading Garmin tracking data it often assumes I have run through people's back yards and living rooms due to the terrain offset

    Google Earth by its very nature and design attempts to show its imagery in 3 dimensions, the images taken by the Google aeroplane show it in 2 dimensions and therefore the image is stretched and distorted over the terrain view. Due to the fact that the surface of the Earth is not perfectly smooth the terrain view is not detailed enough to be an exact match so the photo will be stretched differently. This will cause distortion and mismatching of the final result.

    The other, little known fact is that Google uses a spherical base model, not elliptical (which the Earth is)

    US data uses 30 metre terrain data but as it expands outside to the rest of the world this data is reduced to 90 metre data
    Jerry

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    4 Star Lounger
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    [quote name='t8ntlikly' post='772045' date='24-Apr-2009 07:10']Makes me wish that Virtual Earth had a ruler[/quote]
    It does have a Ruler ... it's Jezza, obviously

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    Super Moderator BATcher's Avatar
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    [quote name='t8ntlikly' post='772035' date='23-Apr-2009 21:50']I have noticed lately that Google Earth is off about 3 blocks or more. Is anyone else noticed this or maybe I have something askew?[/quote]
    In the UK we don't really have 'blocks', but I have never noticed an error where the line of the road is badly off from the actual location of the road itself on the satellite map.
    BATcher

    Time prevents everything happening all at once...

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    Silver Lounger t8ntlikly's Avatar
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    [quote name='Jezza' post='772080' date='23-Apr-2009 16:40']There are various reasons for this which can cause issues. As you probably know, I am an avid ultrarunner and therefore use GPS mapping tools and hardware to map my routes, speed and distance. When uploading Garmin tracking data it often assumes I have run through people's back yards and living rooms due to the terrain offset

    Google Earth by its very nature and design attempts to show its imagery in 3 dimensions, the images taken by the Google aeroplane show it in 2 dimensions and therefore the image is stretched and distorted over the terrain view. Due to the fact that the surface of the Earth is not perfectly smooth the terrain view is not detailed enough to be an exact match so the photo will be stretched differently. This will cause distortion and mismatching of the final result.

    The other, little known fact is that Google uses a spherical base model, not elliptical (which the Earth is)

    US data uses 30 metre terrain data but as it expands outside to the rest of the world this data is reduced to 90 metre data[/quote]

    Thanks Jezza, Coming from the Fleet Tracking side of the GPS market, I have often seen the "going through peoples' yards" as you put it. What really caught me on this, was the fact that on another location look up I went first to Google Earth, and thought that the map was really old, because Virtual Earth put me within a block of the "correct" location, and Google put me in a field about 3 or 4 blocks to the So. When I realized what was going on, I put the pages side by side and was able to get the Google map to the correct location and measure the building that was in question. I almost always now look up the location in Virtual Earth first, and in Google Earth second. As for Virtual Earth having a ruler oh exalted one guess we can't have everything.
    Thanks John
    Teamwork is essential; it gives the enemy other people to shoot at. (Murphy's War Laws #39)

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