On 29.11.17 23:39, Martin Koppenhoefer wrote:
sent from a phone
On 28. Nov 2017, at 06:10, Oleksiy Muzalyev <[email protected]> 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.
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