SimCore

This repository is focused on integrating the Geant4 simulation framework into another event processing framework.

This is centered upon a processor that does the necessary configuring, processing, and persisting steps tied with Geant4.

Detector Visualization

The event processing framework that actually runs this simulation is not well designed for running a visualization. For this reason, a small program has been written that loads the input detector description GDML file and launches an interactive Geant4 terminal.

The simulation is not well configured in this mode, so this interactive terminal should only be used for visualization.

This command is built automatically and is installed as g4-vis. Run g4-vis --help for an explanation on how to use this executable.

Common Geant4 Vis Commands

More detailed documentation for these commands are given in the Geant4 Book for App Developers

In general, you can get started quickly by running the following commands in the given sequence after the Geant4 interactive terminal is launched.

/vis/open OGL
/vis/drawVolume
/vis/viewer/refresh

You will likely want to change the point of view from which you are looking at the detector. The camera working commands is what Geant4 calls these.

Here is a quick reference table for moving the camerage around.

Command	Description
/vis/viewer/pan x y units	Move camera a certain amount left/right (x) and up/down (y) a given amount of units
/vis/viewer/set/viewpointThetaPhi theta phi units	Rotate the camerage to the input direction vector in degrees or radians
/vis/viewer/zoom scale	Zoom towards the center of the image by the input factor

Limitations

The class we use to read-in our GDML and construct the Geant4 detector model makes a large number of assumptions about how the GDML is structured. With this in mind, it is best to use the central detector.gdml file as the "entrypoint" and comment out the different parts of the detector you don't want to see.

Tips and Tricks

• The central detector.gdml file asks for other GDML files, so it is best to run this executable in the same directory as the detector description you want to visualize.

• You can make multi-line comments in GDML by using <!-- ... -->. For example, the magnetic field is not part of the visualization, but is loaded when constructing the detector. You can ignore this by commenting out the magnetic field part of detector.gdml.