By O.A. Isioye, F. A. Fajemirokun
Keywords: GNSS CORS, Height, RTK, ITRF
One of the goals of modern geodesy is the global unification of vertical datums so that height data from them can be properly integrated. Well established vertical geodetic framework, apart from being the backbone of any national surveying and mapping system, also enhances the reliability of elevation data used in spatial information systems for preserving the environment and enhancing sustainable development. The GNSS technology is a three dimensional positioning tool and GNSS heighting can be viewed as a viable alternative to other more conventional forms of height measurement. Nowadays the time of GNSS static baseline determination is almost out-of-date for everyday applications. The current trends are to continuously observe and measure using GNSS, install permanent GNSS base stations or networks and provide real time accurate positioning. These three trends together offer an advanced component of geodetic infrastructure known as a GNSS CORS network. These networks need to have a geodetic datum, meaning that they have to be linked to the available terrestrial reference frames. In some countries/regions, GNSS CORS networks are so well developed and dynamic that they have a more prominent role than the existing classical passive geodetic infrastructure, in reference frame determination, monitoring and positioning. This paper focuses discussion on the trend in GNSS based heighting and their associated accuracies and limitations. The procedures for realizing the link between the GNSS CORS and the available reference frames and effort made by countries and agencies around the world in keeping with trends in GNSS based heighting are discussed. In addition, this paper outlines the limitations and possibilities of real time accurate GNSS height determination in Nigeria.