What is a vertical datum?
A vertical datum is a reference point, plane, or surface from which elevations are measured, e.g., an earth model ellipsoid, the equipotential gravitational surface called the geoid (NAVD88), or the Local Mean Sea Level (LMSL). It is termed a tidal datum when defined by a particular phase of the tide, e,g, Mean Lower Low Water (MLLW). Vertical datums typically represent a terrestrial or earth-based surface to which geospatial coordinates (such as heights, elevations, or depths) are referenced. The vertical datum is the base foundation for nearly all civil and military design, engineering, and construction projects in USACE. Back to top 2. What is the difference between plane and geodetic datum reference systems? A plane reference system uses a flat surface as the origin or 0 elevation. A flat surface does not account for the curvature of the earths surface and should not be used for large projects. Typically these small surveys may not even be referenced to the NSRS and might use a loc
