+Happy Landins Posted July 8, 2004 Share Posted July 8, 2004 I have noticed a problem in the Geocaching site's conversion from LAT/LONG to the British OS Grid reference. The Geocaching algorithm knocks off any leading zeros. This means that with any place with a leading zero the British OS map references don't reflect accurately the LAT/LONG The correct British Grid format should be AA 11111 11111 (2 letters followed by 2 sets of five digits). But the Geocaching algorithm wipes out any leading zero at the front of either of the two sets of five digits. For example For waypoint GCJV0P Geocaching incorrectly gives the British OS Grid reference : SJ 5238 65821 It should read British Grid: SJ 05238 65821 or Similarly, for waypoint GCHW76 the Geocaching British Grid reference shows: TF 62075 1762 It should read as British Grid: TF 62075 01762 I've written to GEOCACHING HQ about this but only had a "got your email" reply so far. This is a serious problem that will need fixing soon. But at least you know why it screws up your OS map reference. Quote Link to comment
+NickandAliandEliza Posted July 8, 2004 Share Posted July 8, 2004 It was noticed last year I don't use them so don't know whether the thread is of help to anyone............. Quote Link to comment
+Team Ullium Posted July 8, 2004 Share Posted July 8, 2004 I only started geocaching this year and to begin with I was fooled by this stripping of leading zeros in the geocaching algorithm but soon cottoned on to what was happening. Even so, I agree with Happy Landins that it should be a simple error to correct and I am surprised that it hasn't been sorted before now as I'm certain we are not the only ones to have noticed this glitch!? I use these British Grid co-ords all the time ... first to find areas on Multimap and OS websites and secondly in the field when taking compass readings on OS maps. I'm willing to bet I am not alone in using OS maps when necessary....and even knowing about this glitch....I have still been caught out on occassion. Ullium. Quote Link to comment
Lactodorum Posted July 8, 2004 Share Posted July 8, 2004 Thanks for reporting this "feature". I've not noticed it as I never use OS co-ordinates (I use Memory Map on the PC/PDA). However I am sure many people use normal OS paper maps for navigating their way around so this could be a problem. I'll push the problem "upstairs" and let you know what happens. Cheers, Lactodorum Quote Link to comment
+The Wildleys Posted July 8, 2004 Share Posted July 8, 2004 I also noticed this bug some time ago. It would be good to have this fixed! I prefer to use OS grid references for most "normal" caches, and to have my GPSr set to BNG, as it's easy to see exactly where you are on the map. Quote Link to comment
+Longfram Kev Posted July 8, 2004 Share Posted July 8, 2004 I use the grid ref and map to find out roughly where the cache is in relation to area and parking etc. then use Lat / Lon to find the exact cache site. Some caches only give Lat / Lon. Although some times I wish you could swap between the two more easily, and didn't have to keep changing the GPS settings. Kev. Quote Link to comment
+Team Ullium Posted July 8, 2004 Share Posted July 8, 2004 Yes it is a bit of a pain when in the field swapping back and forth from British Grid to Lat & Long....and with even some GPS units it is even more onerous as you have to change the map datum also....otherwise you could be quite a bit off Ullium. Quote Link to comment
+The Wildleys Posted July 8, 2004 Share Posted July 8, 2004 You guys might be interested in any replies I might get to this thread. Quote Link to comment
+Happy Landins Posted July 8, 2004 Author Share Posted July 8, 2004 NICE FREE MAP BITS I frequently use the OS Grid references, and this is why and how . . . I have found this useful link on the OS site http://www.ordnancesurvey.co.uk/oswebsite/getamap/ You can punch in the OS ref (leaving no blank spaces) e.g. SJ1234576543 and it will give you a 1:25000 high res printable map showing the exact location of the cache. If you choose the 1:250000 scale this lets you see the roads in the area so you can find where the 1:25000 is located (again centred on the cache) This is a handy hint because it gives you the exact part of the map you want, at the best available scales and, best of all, at no cost! Thank you Mr OS Map maker! Quote Link to comment
+NickandAliandEliza Posted July 8, 2004 Share Posted July 8, 2004 I tend to use Streetmap as it gives you the various conversions including longitude / latitude, post codes, Landranger refs etc and if you want them large maps. Quote Link to comment
+GAZ Posted July 10, 2004 Share Posted July 10, 2004 It was noticed last year I don't use them so don't know whether the thread is of help to anyone............. I do, it gives a quick idea where it is......copy and open autoroute.....paste in the "find" under OS grid......all done in a few seconds, and still be on the cache page at the same time. Quote Link to comment
Mittellegi Posted July 10, 2004 Share Posted July 10, 2004 The "Geo" conversion is also slightly different from that done by my eTrex Legend, and also by the OS document which gives precise formulae (obtained this in hard copy format many years ago, and have yet to discover if they supply now as a pdf (I also have a similar document from the Swiss mapping agency, which uses an oblique Mercator transformation, and which also does not appear to be available officially as a pdf)) I think it all depends on whether you use a rough and ready transformation, a 3-parameter shift, or a 7-parameter shift. Not surprisingly, the Swiss go the whole hog and use 7! If there is any interest, I might be persuaded to scan and pdf either or both of these documents for the usual fee: hint, think multiples of 568ml. BB Quote Link to comment
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