Some Tomtom GPS-Chips (see table below) tell the height above WGS84 ellipsoid instead of producing the height above sea level (ASL). The difference between the height ASL and that above WGS84 ellipsoid is not constant (varies between -106 m and +85 m ) although it varies quite smoothly. The correction for a particular position can be obtained with the online geoid calculator.
|TomTom Models with the height bug|
|Model||height bug||Option for TTTracklog||Option for Height||Option for GPSBabel|
|TomTom ONE 3rd Edition||YES||--agc||h-48.4||-x height,wgs84tomsl|
|TomTom GO 520/520T||NO||none||h0.0||none|
|TomTom GO 720/720T||NO||none||h0.0||none|
- Note: the option for Height is an example where the correction needs to be -48.4 m.