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Google Earth: Long/Lat accuracy?

 
 
Terry Pinnell
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      08-25-2005, 10:53 AM
Anyone know how accurate the longitude & latitude co-ordinates are in
Google Earth please? A couple of test locations I tried (in the
Dolomite area of N Italy) seemed some way off (30" or so) when
compared with an alternative source.

Are there a few easily identifiable locations, ideally in Europe,
which we could use to test?

--
Terry, West Sussex, UK
 
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Dennis Pogson
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      08-25-2005, 10:56 AM
Terry Pinnell wrote:
> Anyone know how accurate the longitude & latitude co-ordinates are in
> Google Earth please? A couple of test locations I tried (in the
> Dolomite area of N Italy) seemed some way off (30" or so) when
> compared with an alternative source.
>
> Are there a few easily identifiable locations, ideally in Europe,
> which we could use to test?


The Greenwich Meridian passes through West
Sussex.................................


 
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Terry Pinnell
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      08-25-2005, 11:08 AM
"Dennis Pogson" <(E-Mail Removed)> wrote:

>Terry Pinnell wrote:
>> Anyone know how accurate the longitude & latitude co-ordinates are in
>> Google Earth please? A couple of test locations I tried (in the
>> Dolomite area of N Italy) seemed some way off (30" or so) when
>> compared with an alternative source.
>>
>> Are there a few easily identifiable locations, ideally in Europe,
>> which we could use to test?

>
>The Greenwich Meridian passes through West
>Sussex.................................
>


Yes, I know, but I'm really suggesting pin-pointing locations and
specifying their true longitude *and* latitude. It could be that my
test was flawed, but it would be reassuring to test GE to within say
5" for both.

--
Terry, West Sussex, UK
 
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Shayne
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      08-25-2005, 11:11 AM
My question is what datm does google use so we can set our gps to that one
before entering the coordinates.
If you are set to the wrong datum on gps you could be off.
After you enter the coordinates in the right datum then you can change the
datum back to the one you use which is probobly wgs84 and you will have the
same location with different coordinates.
"Terry Pinnell" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Anyone know how accurate the longitude & latitude co-ordinates are in
> Google Earth please? A couple of test locations I tried (in the
> Dolomite area of N Italy) seemed some way off (30" or so) when
> compared with an alternative source.
>
> Are there a few easily identifiable locations, ideally in Europe,
> which we could use to test?
>
> --
> Terry, West Sussex, UK



 
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Shayne
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      08-25-2005, 11:34 AM
Just did a search on google datum help file, here's what I got.
As Google Earth currently uses WGS84 datum projection.

"Shayne" <(E-Mail Removed)> wrote in message
news:LHhPe.195737$9A2.111469@edtnps89...
> My question is what datm does google use so we can set our gps to that one
> before entering the coordinates.
> If you are set to the wrong datum on gps you could be off.
> After you enter the coordinates in the right datum then you can change the
> datum back to the one you use which is probobly wgs84 and you will have
> the same location with different coordinates.
> "Terry Pinnell" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
>> Anyone know how accurate the longitude & latitude co-ordinates are in
>> Google Earth please? A couple of test locations I tried (in the
>> Dolomite area of N Italy) seemed some way off (30" or so) when
>> compared with an alternative source.
>>
>> Are there a few easily identifiable locations, ideally in Europe,
>> which we could use to test?
>>
>> --
>> Terry, West Sussex, UK

>
>



 
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Anton Betzler
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      08-25-2005, 04:29 PM
Terry Pinnell <(E-Mail Removed)> wrote:

> Anyone know how accurate the longitude & latitude co-ordinates are in
> Google Earth please? A couple of test locations I tried (in the
> Dolomite area of N Italy) seemed some way off (30" or so) when
> compared with an alternative source.


it's not so bad (30ArcSec), but there is a noticable shift at the hi res
images. I had to move all trackpoints 0.0002 degrees to the East in my
testfile <http://mac-im-netz.de/dateien/tricias.html> to get my foot on
the path ;-)
The roads are more accurate than the satellite image.

hth
Anton
 
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sierra
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      08-25-2005, 04:33 PM
Just checked the corner of my terrace in SE Spain

GPS **.**.32.0" **.**.38.3" Altitude 143m
GE **.**.32.1" **.**.38.8" Altitude 142m

(** degrees and minutes correct), The Google pointer is a bit hit and
miss - doesn't come to a point.
GPS set to WGS84

 
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Terje Mathisen
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      08-25-2005, 07:00 PM
Anton Betzler wrote:

> Terry Pinnell <(E-Mail Removed)> wrote:
>
>
>>Anyone know how accurate the longitude & latitude co-ordinates are in
>>Google Earth please? A couple of test locations I tried (in the
>>Dolomite area of N Italy) seemed some way off (30" or so) when


30 inches is just 75 cm, which is way better than the pixel resolution
in most areas, so I assume you meant something else?

>>compared with an alternative source.

>
>
> it's not so bad (30ArcSec), but there is a noticable shift at the hi res
> images. I had to move all trackpoints 0.0002 degrees to the East in my


So about 6 m offset? Still not too bad. :-)

> testfile <http://mac-im-netz.de/dateien/tricias.html> to get my foot on
> the path ;-)
> The roads are more accurate than the satellite image.


Here in Oslo, Norway the roads have very good coordinate quality, and
GE's images seem to match them very well.

When I display roads on top of the sat images, they all seem to match
within a meter or so, when I just now compared the location of the
closest road junction outside our house, the fit was comparable.

Terje

--
- <(E-Mail Removed)>
"almost all programming can be viewed as an exercise in caching"
 
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Terry Pinnell
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      08-25-2005, 07:03 PM
"sierra" <(E-Mail Removed)> wrote:

>Just checked the corner of my terrace in SE Spain
>
>GPS **.**.32.0" **.**.38.3" Altitude 143m
>GE **.**.32.1" **.**.38.8" Altitude 142m
>
>(** degrees and minutes correct), The Google pointer is a bit hit and
>miss - doesn't come to a point.
>GPS set to WGS84


I'd call that spot on!

--
Terry, West Sussex, UK
 
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Terry Pinnell
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      08-25-2005, 07:10 PM
Terje Mathisen <(E-Mail Removed)> wrote:

>Anton Betzler wrote:
>
>> Terry Pinnell <(E-Mail Removed)> wrote:
>>
>>
>>>Anyone know how accurate the longitude & latitude co-ordinates are in
>>>Google Earth please? A couple of test locations I tried (in the
>>>Dolomite area of N Italy) seemed some way off (30" or so) when

>
>30 inches is just 75 cm, which is way better than the pixel resolution
>in most areas, so I assume you meant something else?
>
>>>compared with an alternative source.

>>
>>
>> it's not so bad (30ArcSec), but there is a noticable shift at the hi res
>> images. I had to move all trackpoints 0.0002 degrees to the East in my

>
>So about 6 m offset? Still not too bad. :-)
>
>> testfile <http://mac-im-netz.de/dateien/tricias.html> to get my foot on
>> the path ;-)
>> The roads are more accurate than the satellite image.

>
>Here in Oslo, Norway the roads have very good coordinate quality, and
>GE's images seem to match them very well.


Both Anton and myself used the " symbol to mean seconds of arc. 30" is
1/120 of a degree, so that's around 3000 feet, or nearly 1km.

--
Terry, West Sussex, UK


>When I display roads on top of the sat images, they all seem to match
>within a meter or so, when I just now compared the location of the
>closest road junction outside our house, the fit was comparable.
>
>Terje

 
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