Fast and accurate relative positioning for baselines less than 20 km in length is possible using dual-frequency Global Positioning System (GPS) receivers. By measuring orthometric heights of a few GPS stations by di€erential levelling techniques, the geoid undulation can be modelled, which enables GPS to be used for orthometric height determination in a much faster and more economical way than ...

the best quadratic unbiased estimation (bque) of variance components in the gauss-helmert model is used to combine adjustment of gps/levelling and geoid to determine the individual variance components for each of the three height types. through the research, different reasons for achievement of the negative variance components were discussed and a new modified version of the best quadratic unbi...

nowadays, combination of gps heights with orthometric heights, derived from precise leveling, is broadly used to obtain point-wise solutions of the geoid, which is called “gps/leveling geoid”. the “gps/leveling geoid” is commonly used to constrain the gravimetric geoid solutions in a least squares surface fitting process. in this paper, unlike the usual application, the “gps/leveling geoid” is ...

Egypt has recentely established a new precise geodetic framework based on the global WGS84 datum to furnish a national GPS-based reference system. For agricultural development along the Nile valley, the National Agricultural Cadastral Network (NACN) has been established with a precision of 1 part per million. However, the orthometric heights of the 112-station network have been computed utilizi...

Interest in the study of global gravitational models has increased recently all over world because it is necessary for height datum transformations. Today International Center Global Earth Models (ICGEM) provides largest collection produced through data from satellite's missions CHAMP, GRACE, and GOCE ... Etc. To allow easy access internet with its more intelligent technologies, one Gravity Org...

The determination of the orthometric height from geometric leveling has practical difficulties that, despite a number of scientific and technological advances, passed a century without substantial modifications or advances. Currently, the Global Navigation Satellite System (GNSS) has been used with reasonable success for orthometric height determination. With a sufficient number of benchmarks w...