GPS Datum - 5 or 6 Figures?
Q. Set my Garmin Geko 201 to Ord survey GB & british but I only get a 5 figure TG number. For example Post Code NR148BH comes up with TG19810 followed by BNG00340.
What do I need to do to correct this & what is the BNG number.
A great site & any assistance would be appreciated.
Nigel Howell, Norwich
A. To use your GPS with Ordnance Survey maps of the UK you need to change the position format of your GPS to BRITISH GRID and the map datum to ORD SRVY GB.
The position will then look something like this:
TG = The 2 letter reference for the 100km grid square;
19810 = The Easting, to 1m resolution;
BNG = 'British National Grid';
00340 = The Northing, to 1m resolution.
If you require a 'normal' six figure grid reference, simply round off the last two numbers on each line; this will give TG198003.
A. The five figure numbers give accuracy to the nearest metre - while the standard three figure grid reference only gives accuracy to the nearest 100m.
See the question on GPS Waypoint Designations for more information
Hope this helps
A. I am really confused with this. I went out yesterday and marked GPS points. My Garmin etrex 10 is set to British Grid and my map datum is ord survey GB. I should be getting points near the River Tummel at Pitlochry but the GPS points looked like this: NN92012 BNG959777 When I put this into UK grid reference finder I keep getting points in the Atlantic off Cornwall!! All I want is a 6 (or preferably 10) figure grid reference number!!! Can anyone tell me what is wrong and how to get what I want??
Jean O, Blairgowrie
A. I'd recommend highlighting the need to set your GPS receiver to British Grid/Ordnance Survey GB early in the information about GPS Waypoints. My Garmin GPS 60 manual is appalling and I've heard of others who really struggle with inputting routes and waypoints because of poor explanations in manuals. Mine was set to Lattitude and Longitude by default and I was puzzled for several days over the difference in the numbers in your GPS text files and the numbers in my Garmin. It was impossible to overwrite them because the fields are completely different of course. I only solved it by reading this answer. Thanks, Mike
Mike Hind, Leeds