[talk-ch] swiss topo open data

Simon Poole simon at poole.ch
Wed Sep 15 10:57:26 CEST 2021

Hi Jean-Daniel

Technically I wouldn't expect the numbers to be exactly the same, as the 
elevation in OSM needs to be metres above above mean sea level as 
defined by the EGM96 <https://en.wikipedia.org/wiki/EGM96> geoid model. 
This is unlikely to really differ a lot, but should be taken in to 
account, if you see differences that are in the 30-50 m range then they 
are likely values above the GPS ellipsoid (and should be corrected).  
See https://wiki.openstreetmap.org/wiki/Key:ele 
might help with checking this.

Are you actually using the 1:25'000 map? If yes I would use Carte 
Nationale SwissTopo and add the scale. On the other hand I'm fairly sure 
their https://www.swisstopo.admin.ch/de/geodata/landscape/names3d.html 
dataset includes elevations too (general warning about the swissnames 
dataset, the names need to be taken with a lot of salt, don't use them 
without checking locally first).


Am 15.09.2021 um 07:43 schrieb Jean-Daniel Bonjour:
> Je constate souvent que certaines altitudes (montagnes, cols...) dans 
> OpenStreetMap sont très imprécises, c'est-à-dire présentent plusieurs 
> mètres de différence par rapport à la carte nationale SwissTopo.
> Donc question concrète : si je corrige ces altitudes erronées dans 
> OpenStreetMap, dois-je ajouter au sommet/col l'attribut 
> "source=SwissTopo" ? Ou est-ce suffisant que, lorsque j'upload le 
> changement, je mette juste dans le champ "Specify the data source for 
> the changes" (j'utilise JOSM), le commentaire "Carte Nationale 
> SwissTopo" ?
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