Geant4 User's Guide for Application Developers - Geant4 - CERN

Detector Definition and ResponseLimitation: a volume with a MANY position can have only this one position; if more than one position is neededa new volume has to be defined (gsvolu()) for each position.• GSDV* routines for dividing volumes are implemented, using G4PVReplicas, for shapes:• BOX, TUBE, TUBS, PARA - all axes;• CONE, CONS - axes 2, 3;• TRD1, TRD2, TRAP - axis 3;• PGON, PCON - axis 2;• PARA -axis 1; axis 2,3 for a special case• GSPOSP is implemented via individual logical volumes for each instantiation.• GSROTM is implemented. Reflections of hierachies based on plain CSG solids are implemented through theG3Division class.• Hits are not implemented.• Conversion of GEANT 3.21 magnetic field is currently not supported. However, the usage of magnetic fieldhas to be turned on.4.1.11. Detecting Overlapping Volumes4.1.11.1. The problem of overlapping volumesVolumes are often positioned within other volumes with the intent that one is fully contained within the other.If, however, a volume extends beyond the boundaries of its mother volume, it is defined as overlapping. It mayalso be intended that volumes are positioned within the same mother volume such that they do not intersect oneanother. When such volumes do intersect, they are also defined as overlapping.The problem of detecting overlaps between volumes is bounded by the complexity of the solid model description.Hence it requires the same mathematical sophistication which is needed to describe the most complex solid topology,in general. However, a tunable accuracy can be obtained by approximating the solids via first and/or secondorder surfaces and checking their intersections.4.1.11.2. Detecting overlaps: built-in kernel commandsIn general, the most powerful clash detection algorithms are provided by CAD systems, treating the intersectionbetween the solids in their topological form.Geant4 provides some built-in run-time commands to activate verification tests for the user-defined geometry:geometry/test/grid_test [recursion_flag]--> to start verification of geometry for overlapping regionsbased on standard lines grid setup. If the "recursion_flag" isset to 'false' (the default), the check is limited to the firstdepth level of the geometry tree; otherwise it visits recursivelythe whole geometry tree. In the latter case, it may take a longtime, depending on the complexity of the geometry.geometry/test/cylinder_test [recursion_flag]--> shoots lines according to a cylindrical pattern. If the"recursion_flag" is set to 'false' (the default), the check islimited to the first depth level of the geometry tree; otherwiseit visits recursively the whole geometry tree. In the latter case,it may take a long time, depending on the complexity of the geometry.geometry/test/line_test [recursion_flag]--> shoots a line according to a specified direction and positiondefined by the user. If the "recursion_flag" is set to 'false'(the default), the check is limited to the first depth level of thegeometry tree; otherwise it visits recursively the whole geometrytree.geometry/test/position--> to specify position for the line_test.geometry/test/direction--> to specify direction for the line_test.geometry/test/grid_cells--> to define the resolution of the lines in the grid test as numberof cells, specifying them for each dimension, X, Y and Z.The new settings will be applied to the grid_test command.108