ESTABLISHMENT OF A BASIC GEODETIC NETWORK FOR TOPOGRAPHIC SURVEYS AT 1/25000 SCALE IN THE MUNICIPALITY OF ALLADA

The geodetic network is an important element in the reliability of geographic information. The insufficiency of the geodetic points on a territory reduces the positioning precision of the elements collected at certain places during the work of topographic surveys carried out on this territory. Surveyors, cartographers and other geographic information actors are often confronted with these kinds of situations in Benin. This is why the National Geographical Institute (IGN) is often asked to put in place two points serving as a basis for carrying out certain punctual topographic works. Thus, in order to contribute to the grid of the Beninese territory by the geodetic points that the municipality of Allada was identified within the framework of the realization of the project. The methodology put in place to achieve the set objectives includes three (03) parts that are: the documentary research, the collection of the data and their treatment. These various steps resulted in the establishment of fifty one (51) new geodetic points added to the existing ten (10) to cover the entire area of the municipality. The average distance between two points being 2.5km. Among the various GPS / GNSS methods used to carry out the observation campaigns of these points, it is the method of the central pivot or static mode with short baselines that has been chosen in order to have centimeter precision. The realization of the assembly chart of the aerial photography photos (PVA) on a scale of 1/25000 on the map of the Allada geodetic points made it possible to assess the position of the geodetic points. The marking of these terminals (signaling of the terminals) on the photos is obtained thanks to the construction of horizontal slabs or terraces of dimension (1.50mx 1.50m and 0.10m thickness above the ground) realized on the spot in such a way that the marker represents the center of the dallette. Durability, precision and homogeneity are the three characteristics of this geodetic network.