A Simple Geometry Editor

GGE is the acronym for Geant4 Graphical Geometry Editor. GGE aims to assist physicists who have a little knowledge on C++ and the Geant4 toolkit to construct his or her own detector geometry. In essence, GGE is made up of a set of tables which can contain all relevant parameters to construct a simple detector geometry. Tables for scratch or compound materials, tables for logical and physical volumes are provided. From the values in the tables, C++ source codes are automatically generated.

GGE provides methods to:

1. construct a detector geometry including G4Element, G4Material, G4Solids, G4LogicalVolume, G4PVPlacement, etc.

2. view the detector geometry using existing visualization system, DAWN

3. keep the detector object in a persistent way, either in GDML format (currently only logical volumes are supported) or Java serialized format.

4. produce corresponding C++ codes after the norm of Geant4 toolkit

5. make a Geant4 executable, in collaboration with another component of MOMO, i.e., GPE, or Geant4 Physics Editor.

GGE can be found in the standard Geant4 source package under the directory environments/MOMO/MOMO.jar. JRE (Java Run-time Environment) is prerequisite to run MOMO.jar, Java archive file of MOMO. MOMO contains GGE, GPE, GAG and other helper tools.

Materials: elements and mixtures

GGE provides the database of elements in the form of the periodic table, from which users can select element(s) to construct new materials. They can be loaded, used, edited and saved as Java persistent objects or in a GDML file. In enviroments/MOMO, a pre-constructed database of materials taken from the PDG book, PDG.xml is present.

Users can also create new materials either from scratch or by combining other materials.

• By selecting an element in the periodic table, default values as shown below are copied to a row in the table.

  Use

  Name

  A

  Z

  Density

  Unit

  State

  Temperature

  Unit

  Pressure

  Unit

  Use marks the used materials. Only the elements and materials used in the logical volumes are kept in the detector object and are used to generate C++ constructors.

• By selecting multiple elements in the periodic table, a material from a combination of elements is assigned to a row of the compound material table. The minimum actions user have to do is to give a name to the material and define its density.

  Use

  Name

  Elements

  Density

  Unit

  State

  Temperature

  Unit

  Pressure

  Unit

  By clicking the column Elements, a new window is open to select one of two methods:

  • Add an element, giving its fraction by weight

  • Add an element, giving its number of atoms.

Solids

The most popular CSG solids (G4Box, G4Tubs, G4Cons, G4Trd) and specific solids (Pcons, Pgons) are supported. All relevant parameters of such a solid can be specified in the parameter table, which pops up upon selection.

Color, or the visualization attribute of a logical volume can be created, using color chooser panel. Users can view each solid using DAWN.

Logical Volume

GGE can specify the following items:

Name

Solid

Material

VisAttribute

The lists of solid types, names of the materials defined in the material tables, and names of user-defined visualization attributes are shown automatically in respective table cell for user’s choices.

The construction and assignment of appropriate entities for G4FieldManager and G4VSensitiveDetector are left to the user.

Physical Volume

Geant4 enables users to create a physical volume in different ways; the mother volume can be either a logical or a physical one, spatial rotation can be either with respect to the volume or to the frame to which the volume is attached. GGE is prepared for such four combinatorial cases to construct a physical volume.

Five simple cases of creating physical volumes are supported by GGE. Primo, a single copy of a physical volume can be created by a translation and rotation. Secondo, repeated copies can be created by repeated linear translations. A logical volume is translated in a Cartesian direction, starting from the initial position, with a given step size. Mother volume can be either another logical volume or a physical volume.

Name

LogicalVolume

Type and name of MotherVolume

Many

X0, Y0, Z0

Direction

StepSize

Unit

CopyNumber

Third, repeated copies are created by rotation around an axis, placing an object repeatedly on a “cylindrical” pattern. Fourth, replicas are created by slicing a volume along a Cartesian direction. Fifth, replicas are created by cutting a volume cylindrically.

Generation of C++ code:

User has to type in a class name to his geometry, for example, MyDetectorConstruction. Then, with a mouse button click, source codes in the form of an include file and a source file are created and shown in the editor panel. In this example, they are MyDetectorConstruction.cc and MyDetectorConstruction.hh files. They reflect all current user modifications in the tables in real-time.

Visualization

The whole geometry can be visualized after the compilation of the source code MyDetectorConstruction.cc with appropriate parts of Geant4. (In particular only the geometry and visualization, together with the small other parts they depend on, are needed.) MOMO provides Physics Editor to create standard electromagnetic physics and a minimum main program. See the on-line document in MOMO.