For the success of an experiment it is important to provide a consistent detector description to simulation, reconstruction and analysis applications from a single source. DD4hep is a framework for the complete description of detector models based on a single source of information. When referring to the detector description this includes, in addition to the geometry and the materials used in the device, also parameters describing e.g. the detection techniques, constants required for alignment and calibration, description of the readout structures and conditions data. The main motivation behind the DD4hep framework is to devise a toolkit that addresses all these issues for all the stages of an experiment. The tool relies on usage of pre-existing and widely used software, combining it into a consistent generic detector description. The main components are the ROOT geometry package (TGeo), which is used for construction and visualisation of the geometry, and the Geant4 simulation toolkit, which can be interfaced via DD4hep to perform detector simulation in complex detector designs.
The core element of DD4hep is the the so-called Generic Detector Description Model (based on ROOT/TGeo ). The generic detector description is an in-memory model that consists of a set of objects containing geometry and auxiliary information about the detector. The aim of the project is to extend support for tessellated solids in ROOT/TGeo and later adopt this implementation to DD4hep to allow import and simulation of CAD designs.