Plane of reference

A reference or reference surface is an imaginary surface on which calculations or measurements are related.

It is often an idealized, simplified model of real surfaces whose metrological and mathematical detection would be impossible or too expensive or inappropriate.

Isosurface

An isosurface connects points of equal property or the same value:

• Isobar = equal pressure surfaces, such as the atmospheric pressure to specify altitudes
• Equipotential surface, such as the gravity field of the Earth and other celestial bodies

Height reference surface

Height reference surfaces of the earth into account the deviation of the average shape of the earth by a bullet, or the deviation of the gravity field iso-surface of an ellipsoid:

• Zero level
• Sea level ( sea level )
• Reference ellipsoid ( Normalellipsoid, Erdellipsoid, Niveauellipsoid )
• Geoid
• Quasigeoid
• Mean sea level (current height reference surface in Germany )
• Equipotential surface, such as the gravity field of the Earth and other celestial bodies

• Dimensional Metrology