Page 1 of 3 Next Regional Centre for Mapping of Resources for Development Ruaraka, Nairobi farah@rcmrd.org Countries have traditionally maintained their own geodetic reference systems resulting in maps in neighboring countries not edge-matching properly at the borders. Apart from increasing the potential for misunderstanding and conflicts, this situation makes it difficult for countries to share information and to work on joint plans and projects. Information on one country's maps could not be easily referenced to that on another country's maps. As we move towards more regional integration, and adopt regional approaches to peace and security, environmental management, trade and industry, we need maps that are continuous across national boundaries. This will be possible through the establishment of a common geodetic reference frame. The African Geodetic Reference Frame (AFREF) was conceived as a unified geodetic reference frame for Africa to be the fundamental basis for the national and regional 3D reference networks. It is expected to be consistent and homogeneous with the International Terrestrial Reference Frame (ITRF) Standards. ITRF is the global reference frame system for the earth as adopted by the International Association of Geodesy (IAG). When fully implemented, it will consist of a network of permanent Global Navigational Satellite system (GNSS) stations, continuous or otherwise, such that a user any where in Africa would have free access to GNSS data nd products, and would be at most 1000 km from such stations. Its full implementation will include a unified vertical datum and shall support efforts to establish a precise African Geoid. All African countries have started embracing the use and applications of GNSS technologies particularly Global Positioning system (GPS) in the various geo information applications, services and products. GPS uses World Geodetic System 1984 (WGS84) WGS 84 system is a modern, global and uniform system best fitting the earth. The International Terrestrial Reference System (ITRS) is the global terrestrial reference system officially adopted by the International Association of Geodesy (IAG). The WGS84 reference system, which is widely used in the world and in Africa as stated earlier, is now identical to ITRS at centimeter level. GPS technology may therefore be used in the implementation of AFREF. GNSS, such as GPS technology is very accessible, precise, economical and sustainable. Most GPS products do not require the user to have in depth knowledge of its technology as their production is application based and user friendly. With the increased use and application of GPS and the requirements to relate the GPS solutions with the already existing mapping products based on local and national coordinates reference systems, there is an urgent need to establish and determine the transformation data to and from such systems to GPS references systems. This shall be achieved on full realization of the AFREF project. The realization of AFREF has vast potentials for geodesy, mapping, surveying, geo-information, natural hazards mitigation, earth sciences, etc. Its implementation will provide a major springboard for the transfer and enhancement of skills and knowledge in surveying, geodesy and especially Global Navigation Technologies (GNSS) with its applications along coastal regions. The concept of a unified geodetic datum for Africa is not entirely new. An effort was made in the 1980s to establish a unified datum using satellite techniques via the African Doppler Survey (ADOS) project. The ADOS project was started in 1982 and was completed in 1986. EUREF is the common geodetic reference frame for Europe. Permanent tracking stations form the backbone of the EUREF network, which are densified at the national level using local campaigns of finite duration. The main components of the network are permanent GPS stations, Operational Centres, Local Data Centres, a Regional Data Centre, Local Analysis Centres, a Regional Analysis Centre and a Network Coordinator. The creation of EUREF took advantage of the existence of various components, adding the network coordinator function to coordinate activities that were already on-going in member countries. EUREF is the European regional component of the Global Network of IGS. As such it delivers free-network solutions from EUREF local analysis centres to IGS for the maintenance of the International Earth Rotation Service (IERS). SIRGAS (Sistema de Referencia Geocentrico para Americas del Sur) is the equivalent of EUREF for the South American countries. It was initially established in 1993 during the International Conference on the Definition of a South American Geocentric Datum, sponsored by the IAG.  Fig. 1 Workflow and products of the photogrammetric/remote sensing process
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