+Firth of Forth Posted March 28, 2003 Share Posted March 28, 2003 I'm about to replace some stone copings, and was told by the stonemason that one had a OS marking on it. Does anyone know whether these are still used? Quote Link to comment
+jeremyp Posted March 29, 2003 Share Posted March 29, 2003 Most OS trigpoints and benchmarks are now obsolete. ------- jeremyp The second ten million caches were the worst too. http://www.jeremyp.net/geocaching Quote Link to comment
+Teasel Posted March 30, 2003 Share Posted March 30, 2003 quote:Originally posted by Firth of Forth:I'm about to replace some stone copings, and was told by the stonemason that one had a OS marking on it. Does anyone know whether these are still used? Ooooh, make sure you keep the plate! (If you don't want it, I'll happily take it off your hands for you, saddo that I am!) Quote Link to comment
Morseman Posted March 31, 2003 Share Posted March 31, 2003 quote:Originally posted by Teasel: quote:Originally posted by Firth of Forth:I'm about to replace some stone copings, and was told by the stonemason that one had a OS marking on it. Does anyone know whether these are still used? Ooooh, make sure you keep the plate! (If you don't want it, I'll happily take it off your hands for you, saddo that I am!) It might not be a plate! The original triangulation work, the 1st Triangulation of the UK, didn't use concrete pillars, it was before concrete came into common use. Marks were made on solid items, like gateposts and corners of buildings. In fact, as well as the trig points, 'benchmarks' were made on corners of buildings as during the 1920s and 30s. These were local marks made when making or checking maps. The marks oten consist of a set of 4 lines chiseled into the stone. A solid horizontal bar, with three others forming an arrow pointed to the centre of the bar, chiselled below it. You might have a bit of a post and packing problem. --... ...-- Morseman Quote Link to comment
DeputyDawg Posted March 31, 2003 Share Posted March 31, 2003 Hope you can possibly build it into the new part of wall, would be shame to lose a bit of mapping history in the city, even if it had it has no value nowdays...p.s. may still show up as 'spot' height on an OS map of the area, SEA..MBBe Quote Link to comment
+Teasel Posted March 31, 2003 Share Posted March 31, 2003 quote:Originally posted by Morseman:It might not be a plate! The original triangulation work, the 1st Triangulation of the UK, didn't use concrete pillars, it was before concrete came into common use. I thought it all began with the Newlyn datum and, later, OSGB36. Didn't realise there were scratches on gateposts and such beforehand! I was expecting it to be a steel plate - part of the network of fundamental bench marks (spot heights) which extended the Newlyn tide guage across the country. (The concrete pillars were for triangulation to extend measurements of glass rods on Hampstead Heath across the country.) I agree that building it back into the wall would be the best course of action. I was just wanting to make sure it didn't end up in some builder's skip! Anyone know of any good material on trigpoints and the like? I've read the OS coordinate systems blurb, and this site, but there must be more out there! Quote Link to comment
+Teasel Posted March 31, 2003 Share Posted March 31, 2003 D'OH duplicate posting! Quote Link to comment
+Daisy&me Posted March 31, 2003 Share Posted March 31, 2003 Does that mean that Newlyn is where 'sea level' is measured from? As I stood on the beach at Hayling Island yesterday my GPS said the elevation was 6ft, which I thought was pretty accurate, but then I got to wondering what sea level meant anyway. Quote Link to comment
+Chris n Maria Posted March 31, 2003 Share Posted March 31, 2003 quote:Originally posted by Daisy&me:Does that mean that Newlyn is where 'sea level' is measured from? In effect Yes. In the UK for Ordnance Survey heights are measured against the mean sea level at newlyn cornwall. Originally all heights above sea level were calculated from this point by the use of leveling which is the use of an inclineometer (spirt level type thing) to show the angle from one position to the other. Obviously it is a pain to keep going to cornwall if yo want to measure a height in scotland - so local benchmarks of known location and height were marked on objects such as walls churchs etc. This is what Firth of Fourth seems to have on his wall. Mapping is just more complicated then it originally seems: the planet is moving, the continents are moving, the seas are moving and land is being deposited/eroded. In order to create maps you have to fix an arbitery point to draw your lines from - like the grenwich meridian & the newlyn datum. These days heights are measured against the Geode - which is a mathematical model of the earths surface. Check out the ordnance survey site for more explinations. Chris Bear rescues a speciality! London & UK Geocaching Resources: http://www.sheps.clara.net Quote Link to comment
+Daisy&me Posted March 31, 2003 Share Posted March 31, 2003 Thanks. I'll be there in the summer so I'll go have a look at the bench mark if I can find it. Quote Link to comment
+Chris n Maria Posted March 31, 2003 Share Posted March 31, 2003 quote:Originally posted by Daisy&me:Thanks. I'll be there in the summer so I'll go have a look at the bench mark if I can find it. It's a bit bigger than a benchmark This might help you find what you are looking for. Bear rescues a speciality! London & UK Geocaching Resources: http://www.sheps.clara.net Quote Link to comment
+The Wombles Posted March 31, 2003 Share Posted March 31, 2003 quote:Originally posted by Morseman:The original triangulation work, the 1st Triangulation of the UK ............. The base for the first triangulation of the country (in 1794) is marked by the Ordnance Survey Stone near Old Sarum, Salisbury. The original reference point was apparently an old canon, cemented upright, upon which the survey equipment was mounted. The canon is still visible today. Dave Quote Link to comment
+Lance Ambu Posted March 31, 2003 Share Posted March 31, 2003 Then came triangular chocolate, made with triangular almonds from triangular trees and triangular honey from triangular bees and so, mr Confectioner please give me ********* Lance It's dark and we're wearing sunglasses. Quote Link to comment
Morseman Posted April 1, 2003 Share Posted April 1, 2003 quote:Originally posted by The Wombles: The base for the first triangulation of the country (in 1794) is marked by http://www.follies.btinternet.co.uk/ordnancetxt.html near Old Sarum, Salisbury. The original reference point was apparently an old canon, cemented upright, upon which the survey equipment was mounted. The canon is still visible today. Dave That's not quite true. The cannon was placed a little while after the start of the 1st Triangulation, witnessed by King George III, on Hounslow Heath in 1784. Sir Joseph Banks, President of the Royal Society, supervised the laying of accurately made glass rods, encased in wood for protection, with each end open to allow the next rod to be accurately placed next to it. From this the first baseline was created and a line from King's Arthur and Hampton Poorhouse was used. The third point, used to measure the angles from each end of the baseline, was a point at St. Ann's Hill. The ends of the line were marked by wooden posts, but these rotted, and old cannon were used instead sometime later. In 1791 the Ordnance Survey took over the Trigonometric Survey. (All taken from The History of the retriangulation of Great Britain 1935 1962 published by the Ordnance Survey) --... ...-- Morseman Quote Link to comment
DeputyDawg Posted April 1, 2003 Share Posted April 1, 2003 What a bit of interest this has stirred, am new to this but wonder why wonder why 'Benchmarking' isn't as popular, or at all, for that matter, as it appears to be in the States....or am I missing something? Interesting though, thanks,Chris,etc, Wombles & Morseman --... ...-- DeputyDawg -.- -. Quote Link to comment
+Firth of Forth Posted April 1, 2003 Author Share Posted April 1, 2003 Good grief! What have I started?? The benchmark in question is in fact carved into the stone as described by 'Morseman'. I have now had a reply from OS saying that they dont keep track of these any more and therefore it does not need to be recarved into the stone. Quote Link to comment
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