Lambertus wrote: > Robert Vollmert wrote: > >> Not sure how common they are, but there's some GPS units with built-in >> barometer (Garmin Etrex Vista HCX at least). The data they provide >> should be good enough to be useful. >> >> > Those sensors need calibration against a known point and can give a huge > offset when uncalibrated. I have such a GPS (GPSmap 60CSx) and never > calibrate it as will most others presumably. As a cyclist all I'm > interested in is the relative altitude differences not the precise > actual altitude as opposed to, say, skydivers. Measuring relative > altitudes is quite accurate (+/- few meters) though. The data is useless > when you want to use it as a primary source, but it should be alright if > you want to use it to determine offsets when compared with a known > point. This requires you to process the GPX nodes trace-by-trace so you > can determine the offset from which the trace started. > > I appose to using altitude data on nodes. E.g. one would not be able to > move a node when that data is added without having to correct/remove the > height data as well. Also adding altitude data invites to add > -otherwise useless- nodes everywhere. I prefer to have altitude data > kept apart from OSM database. Perhaps our own SRTM database > corrected/enhanced using our traces. > maybe one idea for opposing viewpoints would be to have a separate table of node elevations ie node_id, elevation I'm thinking in Rails code that anyone wanting to use elevation could do a "has_one, belongs_to" kind of simple relationship .
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