The dxf file, created with CAD software, using 3Dface or PolygonMesh elements to model flat surfaces, or to model 3D objects, and using the PolyfaceMesh element, to model the single macro-element with three or four nodes. Care must be taken that each 3Dface element has nodes all lying in the same plane and that there is nodal coincidence between one element and the adjacent one; (or at least that the distance between the two nodes is under a certain tolerance that can be managed by the user). The user can manage the accepted tolerance value through specific options available from the Advanced options window of the Model Menu.