[OSM-dev] Altitude data & (cycle) route profiles
osm at na1400.info
Mon Mar 31 15:39:10 BST 2008
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.
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