Good skills and experience in modelling. For example: Autodesk AutoCAD - 2D and 3D modelling in metric system Autodesk Inventor - 2D and 3D modelling in metric system FreeCAD - 2D and 3D modelling in metric system Reengineering from 3d scan to solid body(using Autodesk Netfabb and FreeCAD) and much more either