Geoidet

Geoidet is a term that appears sporadically in geodesy and related disciplines, but it does not have a single, universally accepted definition. In practice, it may be used in different ways depending on the author or context, which can lead to ambiguity.

One common interpretation is that geoidet refers to a geoid-related dataset, such as a geoid height model or grid that encodes the separation between the geoid and a reference ellipsoid. In this sense, geoidet is similar to what is typically called a gravimetric geoid model or a gravity-derived height model used to transform ellipsoidal coordinates to orthometric heights. Another, more informal usage treats geoidet as a determinant-like quantity or a small, geometry-oriented construct associated with the geoid, drawing an analogy to mathematical determinants or curvature measures. These latter uses are not standardized and are mostly found in niche or provisional discussions.

Etymologically, geoidet appears to be a portmanteau combining geoid with an ending such as det (for determinant) or -et (a diminutive or relational suffix). There is no consensus on its origin or precise meaning in major reference works, which contributes to its variable interpretation.

In practical terms, when used as a height or gravity model, a geoidet would be produced by integrating gravity data from gravimetric surveys and satellite missions (for example, GOCE) with GNSS and leveling measurements to define a local vertical datum. The concept supports applications in surveying, navigation, and geodynamic studies, but readers should consult the specific source to understand how that author defines geoidet. See also geoid, geoid height model, gravity anomaly, and reference ellipsoid.