[en] A modular neutron detector, named DEMON, was developed by four laboratories (from Caen, Strasbourg, Brussels and Louvain) to determine accurately the energy and direction of emission of the neutrons. The 99 constituent detectors are formed of liquid scintillator tanks 'viewed' by photomultipliers. The objective of this work was to establish a methodology of detector positioning based on the three-dimensional metrology polar measurements by means of an electronic tacheometer located at the level of the target position. The first part of the paper deals with the geometrical positioning of the detection system while the second part describes the concept of different functions of the programme