[OSM-talk] GPS Altitude vs Pressure Altitude article, Tool for measuring elevation above sea level

[Oleksiy Muzalyev]

On 29.11.17 23:39, Martin Koppenhoefer wrote:
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> sent from a phone
>
>> On 28. Nov 2017, at 06:10, Oleksiy Muzalyev <oleksiy.muzalyev at bluewin.ch> wrote:
>>
>> Besides the number of the satellites increased lately, and the quality of the GPS receivers is also improving. And everyone who has got a modern smartphone has got a GPS altimeter.
>
> Some smartphones and some consumer gps units also feature barometric altimeters. Our consumer GPS units, especially those in smartphones with their suboptimal antennas, are unsuitable for measuring elevation precisely, the accuracy in the z-direction, from what emerged from previous discussions about this, is about 10 times inferior with respect to x/y.
>
>
> cheers,
> Martin

It seems the global sources of elevation are not precise either. For 
example, the OSM shows correctly that the elevation in this part of the 
New Orleans is below sea level: 
http://ausleuchtung.ch/elevation/?lat=30.017679032856247&lon=-90.19947052001955&zm=14&rd=2

However, the Google Map Elevation API shows 0 meters for the same area: 
http://www.enetplanet.com/ . It means the elevation data which was 
entered by the local mappers is more correct. And this is essential 
information for such flood risk zones.

Certainly, one should calibrate an altimeter. For example, measuring the 
elevation at a location with the known elevation. I think it would be 
even better to have both the GPS and the barometric altimeter, and both 
calibrated on the day of actual measurements.

Best regards,

O.