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

[Igor Brejc]

Tom Hughes wrote:
> Stefan de Konink wrote:
>
>   
>> The reason seems to be that some people *think* they are not accurate.
>>     
>
> I think the experiment we conducted at the 4th birthday party showed 
> pretty conclusively that it's not accurate. We were only about 12 foot 
> above sea level (as measured by looking over the wall at the Thames) but
> the various GPS units present reported values from about 0 to about 200 
> foot or so. They also varied radically over time despite the fact that
> we were sat still.
>
> Tom
>
>   
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

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