What is a Vertical Datum?
The Geodetic Glossary (2009) defines height as ‘distance, measured along a perpendicular, between a point and a reference surface’. This definition is concise and direct but leaves a vagueness concerning the reference surface. This reference surface is the Vertical Datum. A datum is required to reach accurate and reliable measures of height above a surface.
The EPSG dataset currently lists 128 vertical datums worldwide. There are various types of height including:
- Ellipsoidal (The difference between the topographic elevation and the ellipsoid)
- Orthometric (The difference between the topographic elevation and the geoid)
- Geoid (The difference between the ellipsoidal height and the
