GeoModeller (old names include 3DWEG, Geomodeller3D) is a methodology and associated software tool for 3D geologic modelling developed by Bureau de Recherches Géologiques et Minières and over the last 20 years. The software is written using Open CASCADE in C++ for the engine (geometry, topology, viewers, data management, ...), Java for the GUI and data are stored in extensible mark-up language XML. GeoModeller has started to revolutionise the working practices, data standards and products of a geological survey as a whole. The software takes into account all structural geology data such as dip, dip directions, strike, hingelines and axialtrace to build the geometry of geological units.