Does anyone know how to tag Swiss altitudes in OSM? The wiki recommends using key ele:wgs84, with values in meters relative to the WGS84 ellipsoid. Near the bottom, the page says it would be even better to use a geoid-relative system, such as EGM96 or EGM2008, rather than WGS84. Although I can (sort of) understand the rationale behind this OSM guideline, does anyone here know how to do this transformation? How to convert Swiss altitude values to WGS84 or EGM, either with the PROJ library or in a custom function?
Background: I’m working on an AllThePlaces script that converts Swiss Open Transport Data to OSM tags. Just like the thousands of other scripts at AllThePlaces, this program will run at least weekly, and it will produce about ~150K point features. In the upstream data feed, many transit stations carry an altitude in “meters above sea level”, which in Switzerland usually means the LN02 reference system. Calling a webservice for so many coordinates multiple times per week would be rather suboptimal; it would be much preferable to do this conversion locally with the PROJ library. (In All The Places, we’re already using PROJ for converting horizontal Swiss LV95 coordinates to WGS84 and are happy with it). Of course, nobody actually cares about elevations in OSM, but I woldn’t mind doing this correctly. If it’s too much bike-shedding, though, I could of course give up and emit the upstream altitudes as ele, ele:ln02 or ele:local.
If somebody here is familiar with altitude conversions, would you mind adding a Switzerland section to the OSM wiki page for Altitude Conversion to WGS84? Thanks in advance 
— Sascha