The Greek origin of the word geodesy means "to divide the Earth" . This definition indicates that geodesy is historically tightly linked to mapping and surveying. But it also reflects that geodesy touches on legal and planning aspects.
In the late 19th century, F.R. Helmert narrowed the definition of geodesy down to "the science of measurement and mapping of the Earth's surface". Although this definition may seem short, it is fundamental, even to modern geodesy.
- It comprises a geometrical component on any scale. Thus classical surveying, positioning and navigation, measurement of deformation from plate tectonics or earthquakes, sea-level determination from satellite altimetry all fit into the framework of geodesy. The geometrical component may be time-dependent, as becomes clear from these examples
Since the shape of the Earth is strongly determined by its gravity field, and since many measurement types refer to the local gravity vector (think of levelling or putting up a theodolite) a second important component of geodesy is the determination of the Earth's external gravity field. Also the gravity field is a time-dependent quantity (tides, seasonal mass redistributions, etc).
- The third leg of geodesy is Earth rotation (or reference frames). All geodetic measurements have to be referenced to a coordinate frame. Depending on the application one may consider for instance a local frame, an Earth-fixed one or even inertial. Reference frames and the transformations between them are also time-dependent, for instance due to Earth rotation or polar motion.
The goal of modern geodesy is to integrate these three legs of geodesy (geometry, gravity and Earth rotation) into a common system. With measurement precision increasing over the years and making use of satellite-based technologies they cannot be treated individually anymore.
From the above you see that geodesy is both a science and an engineering discipline. As a science it belongs to the wider family of Earth sciences like geophysics, oceanography, geology, glaciology. At the University of Calgary, where geodesy is accomodated in the Department of Geomatics Engineering, the engineering side is emphasized.
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