Aimed at scientists, engineers, modelers and other technical users of GIS/mapping applications, this lesson provides a basic understanding of different vertical datums, how they are defined, some of their strengths and weaknesses and how to choose the appropriate datum for a given application. The lesson starts with basic definitions of height and vertical datums and guidance on choosing and working with the appropriate datum for a given situation. It then provides a conceptual introduction to ellipsoidal, geopotential and tidal datums including appropriate uses, examples and pros and cons.
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- Describe how heights and vertical datums are used in surveying.
- Define height as used in the context of surveying and mapping.
- Define vertical datum.
- Provide reasons for choosing different vertical datums.
- Identify types of vertical datums and their associated heights
- Define an ellipsoidal datum.
- Define an ellipsoid.
- Describe the global nature of ellipsoidal datums.
- Define an ellipsoidal height.
- Describe strengths and weakness of ellipsoidal datums.
- Define a geopotential datum.
- Describe earth’s gravity field.
- Explain why geopotential datums help describe water flow.
- Define the geoid.
- Recognize NAVD 88 as the current geopotential datum in the U.S.
- Define orthometric height, geoid height/geoid undulation, and dynamic height.
- Describe strengths and weakness of geopotential datums.
- Define a tidal datum.
- Describe the local nature of tidal datums.
- Explain why tidal datums are important and what they are used for.
- Describe strengths and weakness of tidal datums.
national geodetic survey, benchmark, bench mark, survey mark, vertical datum, datum, standard datum, ellipsoidal datum, geopotential datum, tidal datum, ellipsoidal heights, gravity field, geoid, the geoid, geopotential, geopotential datum, orthometric, orthometric height, geoid undulation, dynamic height, elevation measurement, reference surface, NAVD88, NAVD 88, U.S. national spatial reference system, NSRS, GPS, GNSS, official U.S. datums, ellipsoid, ellipsoid height, U.S. Global Positioning System, Global Navigation Satellite Systems, World Geodetic System 1984, WGS 84, WGS84, earth gravitational model, gravity anomalies, equipotential, equipotential surface, gravity potential energy, geodetic leveling, local mean sea level, International Great Lakes Datum, IGLD, dynamic height datum, mean sea level, zero height surface, ocean dynamic topography, Mean Sea Level, local Mean Sea Level, MSL, Mean Low Water, MLW, Mean High Water, MHW, Metonic Cycle, National Tidal Datum Epoch, National Water Level Observation Network, NWLON, tide station, Center for Operational Oceanographic Products and Services, CO-OPS
