|GPS TIFF Tag GPSAltitudeRef|
TIFF Tag Reference
TIFF Tag GPSAltitudeRef
Indicates the altitude used as the reference altitude.
If the reference is sea level and the altitude is above sea level, 0 is given. If the altitude is below sea level, a value of 1 is given and the altitude is indicated as an absolute value in the GPSAltitude tag. The reference unit is meters. Note that this tag is BYTE type, unlike other reference tags.
The specification defines these values:
0 = Above sea level