GPS Elevation

The GPS coordinates contain only 2 pieces of information: latitude and longitude on the terrestrial globe. Altitude (or elevation, or z value) is the height of the point on Earth, relative to the sea level which is counted as the base altitude (0 meters).

Altitude cannot be calculated from coordinates directly.

However, NASA's satellites scoured the Earth's surface with radars and more or less accurately modeled the elevation of each point on the globe. dCode uses this data to find the altitude of a GPS point.

Example: The altitude of the Greenwich Observatory (latitude: 0, longitude: 51.478) is 37 m

NB: The values given take the sea level as an altimetric reference.

The altitudes found are subject to a margin of error of 1 to 2% (approximately ±10m)

Altitude data represents gigabytes of digits, there are several research studies that offer it. SRTM (Shuttle Radar Topography Mission) data, among the most comprehensive on the globe, is available here (link)