## October 18th 2014, GPS Altitude Correction

← October 16th 2014 Exiv2 | ● | October 18th 2014 Qt 5,4 Beta →

The altitude, which is measured by a GPS device at sea level, is given relative to the WGS84 ellipsoid. This does not correspond exactly with the mean sea level. The difference can be more than 100 meters due to the potato shape of the earth. For example, on one of Sardinia’s beaches, you get a WGS84 altitude of about 50 meters instead of 0 m.a.s.l. (meters above sea level).

We can correct the altitude by subtracting the geoid height. The geoid heights are calculated using the C++ code developed in the EGM project page.

{

point.height -= geoid(point.lat, point.lon);

}

← October 16th 2014 Exiv2 | ● | October 18th 2014 Qt 5,4 Beta →