I'm a member of mountainviews.ie so familiar with their maps and information. I do know they have members of the community that have access to / borrowed high-quality surveying equipment which has resulted in the comprehensive dataset they have.
I would not be surprised if there have been updates in the past 10 years regarding elevation, location, etc. Donal On Sun, 1 Dec 2019, 13:38 moltonel 3x Combo, <molto...@gmail.com> wrote: > On 29/11/2019, Donal Hunt <donal.h...@gmail.com> wrote: > > The latest major revision of WGS 84 is also referred to as "Earth > > Gravitational Model 1996" (EGM96), first published in 1996, with > revisions > > as recent as 2004. This model has the same reference ellipsoid as WGS 84, > > but has a higher-fidelity geoid (roughly 100 km resolution versus 200 km > > for the original WGS 84). > > Hopefully the 2004 revision is close enough to the 1996 one, as it > seems that osm is defaulting to 1996. > > > The tl;dr is that you need to reference which model your peak height is > > measured against. EGM96 is preferred (I'm assuming) because it has higher > > definition and more refined model. > > AIUI from the wiki and taginfo, in an OSM context, the naked "ele" tag > refers to EGM96, and there are subtags like "ele:wgs84" or even > "ele:local" for "whatever's printed on the local signpost". > > I've figured out the overpass query I had in mind: > https://overpass-turbo.eu/s/OCb but it finds basically every peak we > have with an elevation. > > See also > https://help.openstreetmap.org/questions/15397/elevation-of-irish-mountains-why-the-discrepancy-osmwikipedia > which complains the the issue ireland-wide, and notes that the osm > data in other countries is fine. > > All the mountainviews imports basically have > ele:local/ele_local/ele:tm75 (3 keys with first value) and > ele/ele:wgs84 (two tags with second value). I couldn't find a > definition of the "tm75" coordinate system that we got from the > mountainview export, I'm guessing this is an irish-specific > coordinates system, and I have doubts that it is equivalent to the > egm96 that we would like. > > At this point, I have a few questions: > * Are the "tm75" values usable for the naked "ele" tag ? > * If not, can we convert tm75 to egm96 ? > * As a bonus, I think we should remove "ele_local" where we already > have "ele:local" > * Is it ok to edit 790 as a single changeset (once we agreed with the > changes) or do we want to check each individually ? > > * Second bonus (probably for a second stage): is there's any point in > keeping the iemv:* tags ? Might have been a requirement for the import > ? It was done in 2009, maybe it's time to see if they have updated > data. > > > > Cheers. > > _______________________________________________ > Talk-ie mailing list > Talk-ie@openstreetmap.org > https://lists.openstreetmap.org/listinfo/talk-ie > _______________________________________________ Talk-ie mailing list Talk-ie@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-ie