Chapter 4Geodesy

Geodesy is the theoretical and practical framework for utilizing GNSS vector observations and classical terrestrial observations such as angles and distances. While geodesy has much theoretical and mathematical depth, we limit this chapter to operational aspects of geodesy as needed to process GNSS observations and classical terrestrial observations. Not to exclude fundamentals, we first discuss the international terrestrial and celestial reference frames and then turn to the geodetic datum. The 3D geodetic model plays a pivotal role in the subsequent discussion, followed by the more historical 2D ellipsoidal model, and, last but not least, the popular 3D conformal mapping models.

The precise definition of reference frames becomes more important as the accuracy of geodetic space techniques increases. There are three types of frames we are concerned with—the earth-fixed international terrestrial reference frame (ITRF), the geocentric space-fixed international celestial reference frame (ICRF), and the geodetic datum. Specialized literature considers the ITRF and ICRF as an implementation of theoretical constructions such as the international terrestrial reference system (ITRS) and the geocentric celestial reference system (GCRS). In this chapter, we do not make such a distinction. Given the demand of modern geodetic measurement techniques on precise definitions of reference frames, it is certainly not an understatement to say that the definition and maintenance ...

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