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Worst case datum error?

 
 
Thomas Magma
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      02-28-2005, 09:04 PM
Does anyone know what the worst case position error would be when flipping
between two different datums? I heard it could be up to several kilometres
in certain regions around the world. Does anyone know of any reference or
website that might have this information?

Thanks
Thomas


 
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Sam Wormley
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      02-28-2005, 10:11 PM
Thomas Magma wrote:
> Does anyone know what the worst case position error would be when flipping
> between two different datums? I heard it could be up to several kilometres
> in certain regions around the world. Does anyone know of any reference or
> website that might have this information?
>
> Thanks
> Thomas
>
>


The *error* translation from WGS-84 to another datum is typically less
than two meters. If you chose datum A to use with software or maps
using datum B, the "error" due to incompatible datums can be hundred
of meters.

-Sam Wormley
http://edu-observatory.org/maps/waypoints.html
Note datum links


 
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Graham W
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      02-28-2005, 10:23 PM
Thomas Magma wrote:
> Does anyone know what the worst case position error would be when flipping
> between two different datums? I heard it could be up to several kilometres
> in certain regions around the world. Does anyone know of any reference or
> website that might have this information?


I assume you mean the largest distance between identical coordinates in
different datums. I believe the older Japanese datum differs from WGS84
by up to 2 km.
 
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Thomas Magma
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      02-28-2005, 10:58 PM
Thanks Graham,

That is what I meant. Like if two people were told to go to a certain
Lat/Long coordinate but used two completely different datums. How far apart
could these two people be in the worst case scenario.

Do you know where you acquired the info on how the "older Japanese datum
differs from WGS84"?

Thomas

"Graham W" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Thomas Magma wrote:
> > Does anyone know what the worst case position error would be when

flipping
> > between two different datums? I heard it could be up to several

kilometres
> > in certain regions around the world. Does anyone know of any reference

or
> > website that might have this information?

>
> I assume you mean the largest distance between identical coordinates in
> different datums. I believe the older Japanese datum differs from WGS84
> by up to 2 km.



 
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Don Robinson
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      03-01-2005, 06:17 AM
Try
http://www.colorado.edu/geography/gc.../coordsys.html

Don Robinson


 
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Stichting ST
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      03-01-2005, 09:04 AM
On Tue, 01 Mar 2005 09:23:41 +1100, Graham W <(E-Mail Removed)>
wrote:

>Thomas Magma wrote:
>> Does anyone know what the worst case position error would be when flipping
>> between two different datums? I heard it could be up to several kilometres
>> in certain regions around the world. Does anyone know of any reference or
>> website that might have this information?

>
>I assume you mean the largest distance between identical coordinates in
>different datums. I believe the older Japanese datum differs from WGS84
>by up to 2 km.


All datums made after say 1950 do not differ very much between each other.
Some tenth of meters.
Older mapdatums say Swiss CH1903 differs about 200 meter and yes indeed old
Tokio is very far off with about 500 meters.
If you have a program like Ozi Explorer you can experiment with many different
mapdatums. Recalibarte and see where your waypoint moves to.
For a map showing the differences: see this (german) link with picture;
http://www.kowoma.de/gps/geo/mapdatum.htm

Piet
 
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Dennis Pogson
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      03-01-2005, 12:59 PM
Thomas Magma wrote:
> Thanks Graham,
>
> That is what I meant. Like if two people were told to go to a certain
> Lat/Long coordinate but used two completely different datums. How far
> apart could these two people be in the worst case scenario.
>
> Do you know where you acquired the info on how the "older Japanese
> datum differs from WGS84"?
>
> Thomas
>
> "Graham W" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
>> Thomas Magma wrote:
>>> Does anyone know what the worst case position error would be when
>>> flipping between two different datums? I heard it could be up to
>>> several kilometres in certain regions around the world. Does anyone
>>> know of any reference or website that might have this information?

>>
>> I assume you mean the largest distance between identical coordinates
>> in different datums. I believe the older Japanese datum differs from
>> WGS84 by up to 2 km.


If you have a GPS you can find this out by simply standing on one spot and
changing the datums, noting down the Lat/long for each datum.


--
Satellite photocharts of the UK & Ireland
available, excellent detail and accurate
calibration using Oziexplorer.
Remove *nospam* to reply.


 
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Glenn Proctor
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      03-01-2005, 01:19 PM
Stichting ST wrote:

> For a map showing the differences: see this (german) link with picture;
> http://www.kowoma.de/gps/geo/mapdatum.htm


Google's translation of this page is pretty good, certainly enough to get the
gist of what's going on:

http://translate.google.com/translat...language_tools

Glenn.
 
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Graham W
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      03-01-2005, 02:24 PM
Thomas Magma wrote:

> Thanks Graham,
>
> That is what I meant. Like if two people were told to go to a certain
> Lat/Long coordinate but used two completely different datums. How far apart
> could these two people be in the worst case scenario.
>
> Do you know where you acquired the info on how the "older Japanese datum
> differs from WGS84"?


A BBC broadcast several years ago, confirmed by later reading...

Not very helpful, sorry.
 
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Graham W
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      03-01-2005, 02:25 PM
Stichting ST wrote:
> All datums made after say 1950 do not differ very much between each other.
> Some tenth of meters.


AGD66 and AGD72 differ from AGD94 and WGS84 by about 200 metres

 
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