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croesus Occasional Visitor
Joined: Apr 13, 2009 Posts: 3
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Posted: Mon Apr 13, 2009 10:42 am Post subject: Co-ordinate problem with two GPS's |
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I have an Active 10 and a Garmin Etrex H - They seem to give different co-ordinate values for the same place. I think I have set them up accurately - datum etc. e.g.
Active 10: N55 24.544, W1 41.310
Garmin: N55 24.540, W1 41.210
The variation is more pronounced in the W value in all cases. Any ideas? I need to use them together for setting up geocaches (A10) with someone else finding them using the Garmin.
I assume there must be some setup I have missed. |
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collegelecturer Occasional Visitor
Joined: Aug 05, 2007 Posts: 5
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Posted: Mon Apr 13, 2009 12:03 pm Post subject: |
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You can sometimes get electrical interference between two GPS placed side by side with both switched on and this may produce different readings. Use one at time. This may not solve it but is worth trying. |
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croesus Occasional Visitor
Joined: Apr 13, 2009 Posts: 3
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Posted: Mon Apr 13, 2009 12:32 pm Post subject: Co-ordinate problem with two GPS's |
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Thanks for the suggestion.
Tried it GPS's away from each other and off while one gets reading. Still reads W 0.1 of a minute away consistently - I'm not sure how far this is, but it is significant when navigating a cache! |
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mikealder Pocket GPS Moderator
Joined: Jan 14, 2005 Posts: 19638 Location: Blackpool , Lancs
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Posted: Mon Apr 13, 2009 12:57 pm Post subject: |
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Check both devices are using the same datum, quite often this sort of error in reported position can be down to units using different settings - Mike |
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croesus Occasional Visitor
Joined: Apr 13, 2009 Posts: 3
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Posted: Mon Apr 13, 2009 2:04 pm Post subject: Co-ordinate problem with two GPS's |
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Solved!
It is all about Datum - There does not seem a way to change the Active 10 - I assumed (wrongly) that this would be OSGB.
I set the Garmin and the EasyGPS settings not to OSGB, but to WGS 84 - now they both come up with same co-ordinates.
Thanks to those that replied |
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FrequentFlyer Lifetime Member
Joined: Jun 12, 2006 Posts: 962 Location: London
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Posted: Mon Apr 13, 2009 4:15 pm Post subject: |
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What does that sort of error actually mean ? 1Metre out....2, 4, 10 ? Another good reason to carry a map as apposed to tumbling over the edge of a cliff ! |
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philpugh Lifetime Member
Joined: Dec 28, 2005 Posts: 2003 Location: Antrobus, Cheshire
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Posted: Tue Apr 21, 2009 5:33 pm Post subject: |
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FrequentFlyer wrote: | What does that sort of error actually mean ? 1Metre out....2, 4, 10 ? Another good reason to carry a map as apposed to tumbling over the edge of a cliff ! |
In the UK the difference between OSGB and WGS84 in Lat/Long varies from 50-150 metres depending on exactly where in the UK you are. It's very significant.
With the OS mapping in the Active 10 you should get the option to display BNG format - which is the only practical display format for the OSGB datum. You should also be able to set the Etrex to display BNG / OSGB and then you can compare. _________________ Phil |
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M8TJT The Other Tired Old Man
Joined: Apr 04, 2006 Posts: 10118 Location: Bexhill, South Sussex, UK
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Posted: Tue Apr 21, 2009 8:09 pm Post subject: |
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FrequentFlyer wrote: | What does that sort of error actually mean ? 1Metre out....2, 4, 10 ? Another good reason to carry a map as apposed to tumbling over the edge of a cliff ! |
Going N/S 1 degree = 60 nautical miles. 1 nautical mile is 6024 feet so 1 min is 6024 feet, so 0.1 mins is about 602 feet. E/W distances depend on latitude (Cos lat) so at 55N 0.1 min is approx 602 x Cos 55) = about 345 feet. You can do the Imperial to metric conversin yourself if you want. A foot is about 305mm.
So falling off a cliff is a possible scenario unless you look where you are going. |
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