For interest's sake, what's the actual difference like when you convert ODN -> EGM96? (or vice versa?)
Thanks Graeme On Tue, 23 Jun 2026 at 02:08, Graham Whaley <[email protected]> wrote: > Hi, > well, I was just about to pull the trigger and upload the import wiki > page and send the formal import plan email when I (possibly stupidly!) > thought to myself 'better just check what really goes in the "ele" tag'... > well, that opened a can of worms! > Seems that although it is detailed on the wiki that it should be in the > form of EGM96 in metres (https://wiki.openstreetmap.org/wiki/Key:ele). > And what I currently have from the OS trig data is I believe OS ODN ( > https://docs.os.uk/more-than-maps/a-guide-to-coordinate-systems-in-great-britain/ordnance-survey-coordinate-systems/ordnance-datum-newlyn > ). > > It seems there is a long-ish history debating what should go in 'ele' - > for instance one thread with a number of other relevant references buried > in it: > https://community.openstreetmap.org/t/irish-mountains/65758/9 > > I guess I have a couple of questions: > Q1. Is there a consensus in the UK as to what should be put in 'ele'. I > have a feeling most if not all current OSM nodes (for peaks for instance as > well as trigpoints) will be in ODN metres. > Q2. Is there any problem with me adding elevations with three decimal > place precision? That is the data I have, but it seems the majority (but by > no means all) current node data is integer only. > > And a statement: > S1. At a minimum I'd intend to put the ODN in 3 decimal point metres into > the 'ele:local' tag, as also recommended on the 'ele' wiki page > > And an observation: > I still see a few 'ele's with 'ft' in them - I'll see if I can add that > to my list of things to potentially clean up on the way past... > > Right, well, I'm currently struggling to find a method to actually convert > ODN -> EGM96 - I'll keep looking at that. If anybody just happens to have a > tool, or PROJ/GDAL command or some R/sf code with appropriate EPSG > codes...? I've got the OS data loaded as EPSG:7405 which gives me 'OSGB36 + > ODN', but am struggling to get that into 'WGS84 + EGM96' if that makes > sense. > > Oh, if anybody wants a visual preview of the data I now have a slippy map > up and running: > https://grahamwhaley.github.io/OSM_UK_trigpoints/web/index.html > > thanks, > Graham > > > On Tue, 16 Jun 2026 at 17:35, Graham Whaley <[email protected]> > wrote: > >> Hi all, >> thanks to everybody for the feedback and questions. I didn’t hear any >> objections, so I’ll plough on with the work. I’ve written out most of the >> wiki page (locally) and am preparing the official email to the list (as per >> the import guidelines) to formally lay out details and kick off the 14 day >> review period. I’ve been refining the code and am just tickling a slippy >> map to show the current status of the data (HTML and JS not really my >> thing, but I think I can hack something together with leaflet…). Once >> things here are fairly stable I’ll load up the wiki page and send the >> formal email. >> >> Many thanks, >> Graham >> >> >> _______________________________________________ > Talk-GB mailing list > [email protected] > https://lists.openstreetmap.org/listinfo/talk-gb >
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