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Best datum for geocaching/ord survey

 
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JACK2008
Occasional Visitor


Joined: Aug 17, 2008
Posts: 1

PostPosted: Fri Mar 26, 2010 4:16 pm    Post subject: Best datum for geocaching/ord survey Reply with quote

Hi
I am running Garmin Xt, Memory Map (trial) and Oziexplorer.

With Garmain and Memory map I get the same grid reference so the site i'm at, but I really wnt to use Oziexplorer but it seems to be 100m or so metres out when compared. I have tried all the datums/projections without luck.

What is the best datum and projection to provide a OS grid reference on OZiexplorer.

Thanks
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jolly47roger
Regular Visitor


Joined: Jan 11, 2008
Posts: 116

PostPosted: Mon Mar 29, 2010 6:15 pm    Post subject: Reply with quote

In OZI on a PC you need to set the grid to 'BNG' and the Datum to 'Ord Srvy Grt Britn' (right click on the items in the bar above the map display)

You might like GPSU, too, for handling tracks and routes.
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philpugh
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Joined: Dec 28, 2005
Posts: 2003
Location: Antrobus, Cheshire

PostPosted: Fri Apr 09, 2010 8:39 pm    Post subject: Reply with quote

Just to clarify the previous reply.

For OZIExplorer you need to set the datum of your GPS to the same as that which the map was created with. If it is an OSGB map then it probably will be OSGB 36 and transverse Mercator projection. The 100m or so error seems right for a OSGB map being used with WGS84 datum (the usual default datum). YOu can calibrate a scanned map image to any datum with OZIExplorer - assuming you know three co-ord positions in the relevant datum.

The .map file that will be with the OZI mapping file should be readle with a standard text editor and includes the datum and the calibration points also.

EDITED TO INCLUDE: Geocaching information is usually supplied in WGS84 datum as this is the defacto international standard.
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