1 Introduction
This manual introduces the DDRec package which is part of and provides the high level view on the HEP detector geometry that is needed during reconstruction and analysis. In the detailed simulation of the response of a typical High Energy Physics detector very little information is needed in principle on the actual structure of the material distribution in the detector. This becomes obvious if one considers the fact that the Geant4 program is also used in medical applications where the human body is approximated by a voxelised phantom. During the reconstruction of particle trajectories and calorimeter clusters, in particular in the phase of pattern recognition, one typically regards the detector as an abstract structure of measurement surfaces or volumes that generally follow a layering structure. DDRec contains an API that provides this information for reconstruction algorithms, thereby decoupling the details of the actual simulation model used from the reconstruction code. The DDRec API provides the following functionality:
- description of measurement surfaces with coordinate systems for track finding and fitting
- description of non-active surfaces with material properties in order to take effects of multiple scattering and energy loss into account
- conversion of cellIDs assigned to simulated tracker and calorimeter hits to positions of readout cells and vice versa
- access to a list of materials between any two points inside the world volume of the detector
- access to the materials at any given point or along a straight line between two points
- averaged material properties for a list of materials
- computation of radiation and interaction lengths for detector layers, modules or arbitrary sections through the detector
In this manual we describe the different classes in DDRec and how they should be used in the detector geometry constructors as well as in the reconstruction code.
Doxygen code documentation
Please also refer to the code documentation that is created with doxygen for more details on the classes and their members. This documentation can be build with:
cmake -D INSTALL_DOC=ON ${path_to_dd4hep_source}
make install
and will then be available at
${DD4hepINSTALL}/doc/html/index.html