andrewilloughby Posted February 5, 2003 Share Posted February 5, 2003 I have bought a Garmin etrex and want to use it to give accurate Grid References using the British National Grid as used on Ordnance Survey maps. So far the results are very dissapointing, with the gps giving me a reference half a mile or more adrift. Any ideas please? Quote Link to comment
el10t Posted February 5, 2003 Share Posted February 5, 2003 Hi, Its worth checking wich datum your GPS is set to. It sounds like this might be the problem. Rich mobilis in mobili Quote Link to comment
+Bill D (wwh) Posted February 5, 2003 Share Posted February 5, 2003 You need to set the datum and the co-ordinates of your GPS unit according to the map you're working with. I've never used an etrex so I can't tell you where to go in your menus or whatever, but for OS maps you need to set the Datum to OSGB 36 (Ordnance Survey Great Britain 1936) and the co-ordinates to British Grid. Bill Quote Link to comment
Team Galaxy - Simon Posted February 5, 2003 Share Posted February 5, 2003 What level of accuracy is your eTrex reporting when you mark waypoints? If it's low then give the GPSr five minutes or so and accuracy should improve. With a decent signal it should be reporting accuracy of under 20ft. "The sooner all the animals are extinct, the sooner we'll find their money" Quote Link to comment
+Faye & Brad Posted February 5, 2003 Share Posted February 5, 2003 I have had a look, and on the eTrex Legend, it is on the Main Menu / Setup / Units. Position Format is where you change to "British Grid", and Map Datum gets set to "Ord Survey GB" Hope this is of some help. Quote Link to comment
+Nia Posted February 5, 2003 Share Posted February 5, 2003 we have the yellow e-trex and had exactly the same problem, when we started. You can keep changing it, but we kept forgetting and leaving it on the wrong setting. this can be very annoying. I recomend you use something like "Waypoint Workbench" a free spreadsheet by Chris and Maria. there is a link to their site at the bottom of all their posts. Tech-no notice Quote Link to comment
+Chris n Maria Posted February 6, 2003 Share Posted February 6, 2003 quote:Originally posted by Nia:I recomend you use something like "Waypoint Workbench" a free spreadsheet by Chris and Maria. there is a link to their site at the bottom of all their posts. What like this..... Bear rescues a speciality! London & UK Geocaching Resources: http://www.sheps.clara.net Quote Link to comment
+paul.blitz Posted February 6, 2003 Share Posted February 6, 2003 quote:I have bought a Garmin etrex and want to use it to give accurate Grid References using the British National Grid as used on Ordnance Survey maps. So far the results are very dissapointing, with the gps giving me a reference half a mile or more adrift. There is approx 100m difference between the datums for WGS84 (as used by GPS satellites & geocaching) and OS maps. As others have said, you need deg/min readout on a WGS 84 datum for geocaching, and British Grid with OSGB datum to use maps. Ozi Explorer (PC mapping / GPS software) is very good as it supports use of 2 setups at once (ie WGS84/OSGB) so I can calibrate maps to British grid (using the inherent grid on the map), then do everything else in WGS84. Paul Team Blitz White gravel? What white gravel? I can't see any.... heck, who cares! Quote Link to comment
andrewilloughby Posted February 8, 2003 Author Share Posted February 8, 2003 Thanks for the replies so far. I have it set to British National Grid, but I was not aware of different 'datums'. This seems to be the problem and thanks to those who told me I need to use OSGB 36. Unfortunatly this is not listed on my etrex. Ah, just found ord srvy GB sounds like that might be the right one! Quote Link to comment
+John Stead Posted February 9, 2003 Share Posted February 9, 2003 Ordnance Survey GB is the right datum. Quote Link to comment
andrewilloughby Posted February 9, 2003 Author Share Posted February 9, 2003 It works now, thanks everyone. The yellow etrex is not destined to be a paperweight. Quote Link to comment
4x4xFinch Posted February 12, 2003 Share Posted February 12, 2003 quote:As others have said, you need deg/min readout on a WGS 84 datum for geocaching, and British Grid with OSGB datum to use maps. I'm using GRB36 and OSGB as main datum. I thought that I'd be able to get faily close using an OS map grid and then still using the OSGB datum on my GPS, find the Cache. Is this not the case? Can you point me to other treads on this? quote:Ozi Explorer (PC mapping / GPS software) is very good as it supports use of 2 setups at once (ie WGS84/OSGB) so I can calibrate maps to British grid (using the inherent grid on the map), then do everything else in WGS84. How does this work in practice? thanks, Simon Quote Link to comment
+jeremyp Posted February 16, 2003 Share Posted February 16, 2003 quote:Originally posted by 4x4xFinch: I'm using GRB36 and OSGB as main datum. I thought that I'd be able to get faily close using an OS map grid and then still using the OSGB datum on my GPS, find the Cache. Is this not the case? The waypoint has its position posted in degrees and minutes in WGS84 and as a British grid ref which is always in OSGB36. If you type the lat/long into your GPS to make a waypoint, make sure you are in WGS84 mode when you type it in. If you type in the British grid ref, make sure you are in OSGB36 mode when you type it in. Once you have the waypoint in the GPS you can change datum and the coordinates will be changed automatically to always refer to the same spot on the ground. ------- jeremyp The second ten million caches were the worst too. http://www.jeremyp.net/geocaching Quote Link to comment
101325 Posted February 19, 2003 Share Posted February 19, 2003 I've been using a very bog standard road atlas, a calculator and a milimetre scale with my eTrex venture, to produce GPS waypoints accurate to about 200 yards. good enough for motorist navigation, and I was very pleased in that I did not need OS Maps or even access to the internet. Quote Link to comment
+Lance Ambu Posted February 19, 2003 Share Posted February 19, 2003 quote:Originally posted by 101325:I've been using a very bog standard road atlas, a calculator and a milimetre scale with my eTrex venture... That sounds almost painful. I have used GPSU (other programmes are available) to scan maps and calibrate with a couple of known points then plot waypoints by mouse click. Some programmes will accept Autoroute "pins" as well. I also have a Venture, but I'm not sure that mapsource is a good buy for this unit. Lance It's dark and we're wearing sunglasses. Quote Link to comment
+Pooter Posted February 20, 2003 Share Posted February 20, 2003 One of the good things about the Magellan Meridian is that you can set up two map datums for the machine to use and then use the rocker switch to flick between them. Quote Link to comment
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.