[OSM-dev] Altitude data & (cycle) route profiles

MilesTogoe miles.togoe at gmail.com
Mon Mar 31 16:51:11 BST 2008

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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