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When tagging mountaintops I'd like to add elevations to them, but I'm not sure if it's permissible to use the elevations given in maps. I have GPS data as well and could use those, but in case of mountain tops I suppose the 'official' figures on the maps are more accurate.

If I can use map data for this purpose, what 'source' tag do I use?

asked 28 Jul '11, 10:57

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kfj
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You should not copy anything from anything we do not have permission for. but you could use out of copyright maps such as NPE (GB).GPS devices with calibrated barometric altimeters (such as garmin vista HCX) give accurate heights but that will take some time. To catch copiers maps sometimes have incorrect data so if you copy this trap data they may catch you and us out.

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answered 28 Jul '11, 11:19

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andy mackey
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+1 for not copying from existing map, certainly copyrighted. Concerning mountaintops, the information might be available in public-domain databases; you'll have to do a bit of research to find that.

(28 Jul '11, 12:23) Vincent de P... ♦

Concerning altimeter-assisted GPS measures, I've found (owning both a vista hcx and a gpsmap 62s, and comparing with maps and fellow hillwalkers) that they are less reliable than GPS-only measures. Altimeters are influenced by the weather, after all. On garmin devices, the map screen will give you the gps-assisted measure while the satellite screen will give you the gps-only measure. Be sure to measure on a clear day and using the "average waypoint" feature. Ideally, measure multiple times at a few hours interval minimum.

(28 Jul '11, 12:23) Vincent de P... ♦

I'm working in extremely rugged terrain, often days from the nearest road. Revisiting in better conditions is often not an option. I use a vista hcx and I can let it average my peak measurements, 'calibrating' the altimeter to use GPS altitude. I usually hang around on peaks for a while doing panorama photography there. So that's what I'll use if I can't find a proper quote somewhere in the public domain.

(28 Jul '11, 14:00) kfj
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Makes me think of a feature: If people could all contribute their own elevation readings and the database would average over them, we might arrive at a very good value in the end. Just an idea.

(28 Jul '11, 14:00) kfj

Your answer 'not copy anything from anything' scares me a bit: how about toponyms? Am I supposed to ask the local fauna or are these considered public domain? I thought the no copy policy referred to the graphic rendition of the topology in the maps. I'm not trying to be contrary, I just want to get it right.

(28 Jul '11, 14:00) kfj

anything we do not have permission for.unless out of copyright is my understanding of the situation. but I agree its a pain,the OS open data debate for example

(28 Jul '11, 14:23) andy mackey
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The accuracy of GPS elevations is quite low (around 50 meters) because the system was set up to be much more accurate horizontally than vertically. If you use a barometric tool you have to frequently calibrate it (and ideally observe the air pressure at a fixed point).

In this context I'd also like to mention that there is different reference systems for elevations (i.e. you can not directly copy elevation data from one system to the other without transforming it). In OSM you should use WGS84 or specify the reference system (e.g. ele:<refsys>=123m)

(28 Jul '11, 14:51) dieterdreist

In my area 200 feet above mean sea level (Cambridgeshire uk) is high and the baro seems accurate against other map contours. I now see that barometric elevations wouldn’t be good in your case, because of the time taken to get to these area would allow pressure changes due to atmospheric conditions. Its good you have found extended averaging should be a good source of accurate elevations.

(30 Jul '11, 17:12) andy mackey

I agree that some of the copyright stuff seems over the top, But in my opinion the main threat to OSM is the copyright legal issue which I’m sure you understand as your question indicates. I press the point for anyone who thinks it is a trivial issue.

(30 Jul '11, 17:13) andy mackey
showing 5 of 9 show 4 more comments

First off, the altitude stated on a national topomap will be in relation to a) the local projection and b) the local height datum. Peaks located on boundaries may have equally valid heights differing by upto several metres . A barometric height will presumably also be calibrated to a known height in a given national datum. OSM does not have any kind of standard for elevation data.

Second, copying height data from maps is indeed fraught (as stated in a previous answer). However, it is clear that some usage of map-derived height data has been tolerated by national mapping agencies for many years. In the UK, the Scottish Mountaineering Club has published Munro's Tables since 1891. The heights and, indeed, criteria for inclusion have all been derived from Ordnance Survey Maps. More recent compilations, such as Corbett's Tables, the Nuthalls, and the labour of love which is the Marilyns all rely on deriving height, prominence and geolocation information from Ordnance Survey maps. I am unaware of any legal opposition to this practice from the Ordnance Survey. Most alpine climbing guides (FAC,SAC,DAV,OeAV etc.) include a substantial amount of derived elevation data (and other things like toponyms): although these are usually critically assessed and errors in mapping toponyms usually noted. Again I have not noted copyright notices or other forms of permission/licenses for these works.

Lastly, many heights of well-known peaks can be assumed to have entered the public domain: I can recall off the top of my head heights for most Welsh 3,000 ft peaks, several Munros and a number of alpine peaks. Additionally in parts of Europe unnamed peaks will often be referred to by their height in guidebooks and elsewhere in the form Point/Punte/Punto/Punkt ####. An example is this peak in the Engadine Dolomites: Pt. 3044.

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answered 28 Jul '11, 15:56

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SK53 ♦
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as far as mountaintops go, I suspect that the GPS elevation might be reasonably precise - at least there is not much around to be in the satellites' way. From my (limited) experience I'd say the numbers I get from my vista hcx are usually at most a few metres off what's on the signposts on the summits. BTW - are the elevations and topnyms on such signposts (as deployed by the park administration in my trekking area) in the public domain and hence usable?

(28 Jul '11, 16:52) kfj

this page might give some more information regarding GPS altitude readouts... http://gpsinformation.net/main/altitude.htm

Most countries have a point that their sea level is measured from... e.g Newlyn Tidal Observatory in the UK, Alicante Town Hall in Spain... What I don't know is whether they consider mean sea level to be the same in such places? Any ideas anyone?

(29 Jul '11, 18:04) c2r

the information regarding GPS altitude measurements you(c2r) quote seems to be ten years old. While the geometric argument is of course still valid, I think the accuracy of today's devices is much higher. And on my mountain peaks I should have an as unobstructed as possible position :)

(30 Jul '11, 09:05) kfj

Hello, that's true, but the principles still hold - I've got a GPS device which when connected to OSMtracker 'shows' error on the GPS tab.. mountains, forest, tall buildings etc. still cause the accuracy to decrease, even when locking on several satellites...

(01 Aug '11, 07:35) c2r

but when you're on top of the mountain, the mountain helps, rather :)

(01 Aug '11, 08:05) kfj

Note in Canada Canvec has provided an open source information, so if you properly attribute the source you can use their data. Of course if the particular mountain you are on has a sign then you can use source=local_knowledge
For example one mountain I've hiked up numerous times in Joshua Tree National Park has this sign

... alt text

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answered 04 Aug '11, 16:43

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Sundance
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thanks for clarifying the issue with signposts. I've been sloppy with signposts insofar as I haven't made a specific note when entering the waypoint into my GPS, so from now on I'll use a specific symbol for waypoints that refer to signposts, so I can use them with the local lnowledge tag. I'll try and make a photo of each as well for convenient reference.

(05 Aug '11, 09:37) kfj

A camera is great for taking notes,if you sync the time on camera to the GPS they can be nailed to the location (geo tagged) with JOSM and other software , there more in the wiki about this and Dictaphone notes

(05 Aug '11, 09:48) andy mackey
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question asked: 28 Jul '11, 10:57

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last updated: 05 Aug '11, 09:48

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