+espargosas Posted August 22, 2006 Share Posted August 22, 2006 The OS 1:50,000 maps that I use when L.D. walking in the U.K. operate through national grid references. I would like to relate these grid references to the Northings and Westings of my GPS. OS maps provide the longitude and latitude references in the margins. But it's very fiddly work relating the one to the other. Questions: (a) Is there an easy way to relate the two readings? and ( can these latter references be used as they are or is it necessary to apply a variation factor for magnetic/true north? If this calculation results in only a small difference it may be easiest to ignore it as, in any event, GPS is not super accurate. Thanks for any help anyone can offer. mikepease@sapo.pt Quote Link to comment
+rutson Posted August 22, 2006 Share Posted August 22, 2006 There is no easy way to convert between them, the calculations are hugely complicated, believe me, I've written conversion software. However, most if not all GPSRs can be set to show OSGB references. What receiver are you using? Quote Link to comment
+melmur Posted August 22, 2006 Share Posted August 22, 2006 If you have a PPC, then OSGPS does it easily enough. http://www.freenetpages.co.uk/hp/barrydavies/osgps_main.html So does Memory Map for the PC/PPC, but you have to pay for it. You could also use something like this: http://www.nearby.org.uk/conversions.cgi of which there are hundreds around, just google for them. There is also one on the OS website, but I can't find it at the moment. Quote Link to comment
+melmur Posted August 22, 2006 Share Posted August 22, 2006 (edited) Just seen the bit about magnetic variation in your first post: It doesn't matter if you're just using lat/long & grid references. GMA (Grid/Magnetic Angle) only applies when converting grid bearings to a magnetic bearings & back. Edited August 22, 2006 by melmur Quote Link to comment
NickPick Posted August 22, 2006 Share Posted August 22, 2006 The converter (for the PC) which the Ordnance Survey recommended me is GridInquest, available at Quest Geo Solutions webpage. you need to register, but it's free and harmless. The OS also have an online version of the converter at National GPS Network The OS will also let you download the formulae to write your own converter, or a DLL to incorporate into your own software. Saves all of that nasty mucking about with polynomial transformations! Quote Link to comment
+melmur Posted August 22, 2006 Share Posted August 22, 2006 The OS also have an online version of the converter at National GPS Network Yep, that's the one I was thinking of. Quote Link to comment
+Daisy&me Posted August 23, 2006 Share Posted August 23, 2006 Most GPSs will optionally show your coordinates in OSGB grid references. Are you sure your's doesn't? Quote Link to comment
+rutson Posted August 23, 2006 Share Posted August 23, 2006 There's an echo in here... Quote Link to comment
lampsh Posted September 5, 2006 Share Posted September 5, 2006 I have a Nuvi 310 which allows you to enter grid refs in OS format (then seems to inaccurately convert them to lat/lon) but I cannot see how to get it to display current loc using the OS grid refs. Thanks for the useful responses on converters, though, it does help me with my previous posting which seems, strangely, to have vanished... Quote Link to comment
+SierraFive Posted September 6, 2006 Share Posted September 6, 2006 The OS 1:50,000 maps that I use when L.D. walking in the U.K. operate through national grid references. I would like to relate these grid references to the Northings and Westings of my GPS. OS maps provide the longitude and latitude references in the margins. But it's very fiddly work relating the one to the other. Questions: (a) Is there an easy way to relate the two readings? and ( can these latter references be used as they are or is it necessary to apply a variation factor for magnetic/true north? If this calculation results in only a small difference it may be easiest to ignore it as, in any event, GPS is not super accurate. Thanks for any help anyone can offer. mikepease@sapo.pt Try www.maptools.com they make ruler like scales that you can put against a OSGB map and read off the latitude and longitude with ease. (You will need a large ruler in the first instance though to join up the lat / lon grid on your OSGB map so that you have something to put the scale against). Maptools.com are an American company but they will supply to the UK. I bought a couple of scales and they will fit in a standard envelope so shipping is dirt cheap too! Quote Link to comment
barryhunter Posted September 6, 2006 Share Posted September 6, 2006 You will have to be slightly careful using the Lat/Long grid's on at least Landranger, Explorer/Outdoor Leisure maps, as the Lat/Long is in the OSGB Datum, wheres its more typical (eg on geocaching and usually on a GPSr) to use the WGS84 datum. The difference varies but can be about 200m's out, which could be a problem if working quite accuratly. Quote Link to comment
+espargosas Posted September 6, 2006 Author Share Posted September 6, 2006 You will have to be slightly careful using the Lat/Long grid's on at least Landranger, Explorer/Outdoor Leisure maps, as the Lat/Long is in the OSGB Datum, wheres its more typical (eg on geocaching and usually on a GPSr) to use the WGS84 datum. The difference varies but can be about 200m's out, which could be a problem if working quite accuratly. Barry, Many thanks for your helpful comments. I have gone ahead and ordered a conversion ruler from 'Maptools', also recommended via Groundspeak. First time I've used. A great communication tool. Mike 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.