[OSM-dev] gpx elevation data for given bounding box?

[Igor Brejc]

Karl Newman wrote:
> On Sat, Sep 13, 2008 at 2:06 PM, Igor Brejc <igor.brejc at gmail.com 
> <mailto:igor.brejc at gmail.com>> wrote:
>
>     Some units (Garmin eTrex Vista, for example), use barometric altimeter
>     as the only source for the elevation data. Which means that it's
>     reliable only if calibrated regularly (every few hours, if weather
>     changes). Otherwise the data is more or less useless for mapping
>     purposes - errors could be in hundreds of meters. So you cannot
>     rely on
>     such GPX elevation logs.
>
>     Igor
>
>
> Garmin units with barometric altimeters use an autocalibration method 
> where the GPS altitude is used as an input to correct for pressure 
> changes. According to some users' tests, if set up properly initially 
> (i.e., calibrate it to a known elevation or wait about half an hour 
> before starting out), it works quite well, maintaining accuracy within 
> 5 to 10 meters the entire day. See here for one such testimonial (not 
> the best documentation of an experiment, but it's what I could find 
> quickly): http://forums.groundspeak.com/GC/index.php?showtopic=187738
>
> Karl
Funny, I thought my unit (Vista Cx) did not have the autocalibration 
feature. Now I did a search through the manual and found it (and it was 
already turned on). Karl, thanks for the info :)

Igor

-- 
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