Geodesy - Heights

In geodesy, point or terrain heights are "above sea level", an irregular, physically defined surface. Therefore a height should ideally not be referred to as a coordinate. It is more like a physical quantity, and though it can be tempting to treat height as the vertical coordinate, in addition to the horizontal coordinates and, and though this actually is a good approximation of physical reality in small areas, it quickly becomes invalid for regional considerations.

Heights come in the following variants:

  1. Orthometric heights
  2. Normal heights
  3. Geopotential heights

Each has its advantages and disadvantages. Both orthometric and normal heights are heights in metres above sea level, whereas geopotential numbers are measures of potential energy (unit: m² s−2) and not metric. Orthometric and normal heights differ in the precise way in which mean sea level is conceptually continued under the continental masses. The reference surface for orthometric heights is the geoid, an equipotential surface approximating mean sea level.

None of these heights is in any way related to geodetic or ellipsoidial heights, which express the height of a point above the reference ellipsoid. Satellite positioning receivers typically provide ellipsoidal heights, unless they are fitted with special conversion software based on a model of the geoid.

Read more about this topic:  Geodesy

Famous quotes containing the word heights:

    “Men go out to admire the heights of mountains, the huge waves of the sea, the broadest spans of rivers, the circle of ocean, the revolutions of stars, and leave themselves behind.”
    —St. Augustine (354–430)

    “Forgetting: that is a divine capacity. And whoever aspires to the heights and wants to fly must cast off much that is heavy and make himself light—I call it a divine capacity for lightness.”
    —Friedrich Nietzsche (1844–1900)

    “This monument, so imposing and tasteful, fittingly typifies the grand and symmetrical character of him in whose honor it has been builded. His was “the arduous greatness of things done.” No friendly hands constructed and placed for his ambition a ladder upon which he might climb. His own brave hands framed and nailed the cleats upon which he climbed to the heights of public usefulness and fame.”
    —Benjamin Harrison (1833–1901)