OpenStreetMap
See TL08/T16 - Egleton.
I went out today to compare my Garmin eTrex 10’s idea of the location of this Triangulation Pillar with the Ordnance Survey National Grid reference of 486466.32,306589.94 .
I am pleased to report that the Garmin read 52N39.0111 0W43.399 (WGS84 decimal minutes), the closest representation of the Ordnance Survey data. I converted the National Grid reference at Coordinate transformation tool to give 52N39.010738 0W43.399301, note that not all online co-ordinate conversion tools agree!
This pillar has a flush bracket with the number S6767.
I have added this as a point, in changeset 45201297.
I do not know that it is in the perfectly correct place as I do not know that Bing’s idea of the absolute position of points on the earth’s surface is the same as mine. OK, the location of my new point is 52.6501638, -0.723312, and it should be 52.6501790, -0.723322. Do I need to fix this, and if so, how?
Discussion
Comment from SomeoneElse on 16 January 2017 at 12:01
Re the elevation, I probably wouldn’t use the elevation from an eTrex 10 as I don’t think that’s got an altimeter in it and is just reporting the GPS altitude. It might be close to the real value, or it might not. Personally I’d also be careful with an altimeter-equipped value, based on changing weather conditions and how recently calibrated.
However, any trig point that’s been there for 50 years or so is probably going to be on an out of copyright map somewhere - presumably you could use the elevation from that?
Re “Bing’s idea of the absolute position of points on the earth’s surface” - that’s an excellent question. Imagery such as Bing’s can be offset (though it’s less of a problem than it once was) so it makes sense to check available compatible sources such as GPS traces as well. In the absense of any other information where you’ve put it is as good a place as any. The general way things work in OSM is that things get added and then refined later - don’t get worried about “I might not have put it in exactly the right place” - someone can always move it later.
For info - if you’ve got any general questions you can always ask over at the help site: https://help.openstreetmap.org/questions/ .
Finally, welcome! You actually missed a mapping party at Scalford just up the road from you at the weekend :)
Comment from Peter Fowler on 16 January 2017 at 12:59
Comment from SomeoneElse on 16 January 2017 at 13:32
The wiki pages often suggest other tags that I don’t know about (I had no idea that “type=triangulation” was used, for example). Looking at the area in an OSM editor, I can see that the “NLS - OS 1:25k 1st Series 1937-61” map that’s available as background does show it as being just above a 475’ (145m) contour, so somewhere in that region would do I guess. Depending on the editor you’re using you may need to zoom out to zoom level 16 to see this background.
Re mapping parties, the talk-gb mailing list is the place that most things will be mentioned. There may also be discussion in the talk-gb channel on IRC. There are regular active meetups (usually in pubs) in at least London, Birmingham, Notingham/Derby and Edinburgh. I think someone has recently been trying to organise something in Oxford too. Mapping meetups are rarer - I’d guess April/May for the next Midlands one.