A datum in this context is simply a known point from which relative measurements are made. Each measurement MAY use a different datum for a type of measurement.
Some possible data used for altitude measurements.
| Datum | Name | Description |
|---|---|---|
| AGL | Above ground level | The altitude from ground level at a known lat/long. |
| MSL | Mean sea level | The mean sea level for a known lat/long or region (e.g. US). |
| SFC | Surface | The surface, typically 0 AGL. |
| SPS | Standard pressure setting | The flight level in meters as measured at standard pressure setting (1013.2 mb). Note: This is a moving datum. |
| WGS84 | WGS84 (GPS) | The WGS84 datum used by GPS. |