KAHIBARO
20.4. Visualization Commands
Table of Contents
Opening viewers
In Geant4, visualization is controlled from the command line with macro commands that start with /vis/. Before you can see your geometry or tracks, you must open a visualization driver. The choice of driver depends on how you built Geant4 and which visualization libraries are available on your system.
The most common drivers for beginners are OpenGL and Qt. If you built Geant4 with Qt support, the Qt OpenGL viewer gives you a window with menus, mouse interaction, and a convenient GUI. The basic command to open a viewer is:
/vis/open <driver-name>
For example, if you want to use the Qt OpenGL viewer, a typical command in a macro file looks like:
/vis/open OGL 600x600-0+0
Here, OGL selects the OpenGL driver, and the rest configures the window size and position. The exact syntax can differ slightly between Geant4 versions and platforms, but the pattern is the same: specify a driver name and optional window parameters.
If you are not sure which drivers are available, you can ask Geant4 to list them with:
/vis/list
This prints the available visualization drivers in the terminal or session window. You can then select one by its short name in /vis/open.
Whenever you first open a viewer in a new session, you should also initialize the visualization system with:
/vis/initialize
In many example applications, this is already called for you in the main macro. If it is missing, geometry might not appear in the viewer even if the window opens correctly.
Once the viewer is open, you can start a run and then see particle tracks and hits drawn automatically if the example or your own code has enabled trajectory and hit drawing. If nothing appears, check that the viewer is open, visualization is initialized, and that you have actually created and run at least one event with /run/beamOn.
Drawing geometry
After you have an open viewer, you need to issue commands that tell Geant4 what to draw and how to draw it. The central command for this is:
/vis/drawVolume
Without arguments, /vis/drawVolume draws the world volume and everything inside it as defined in your DetectorConstruction class. This is usually the command you use first to verify that your geometry is correctly constructed and positioned.
You can also draw a specific logical or physical volume by name, for example:
/vis/drawVolume myDetector
In this case, myDetector must be the name assigned to a volume in your C++ geometry code. Drawing a single volume can help you debug a particular detector element without clutter from the rest of the setup.
To make sure that the viewer reflects the latest geometry changes, use:
/vis/scene/create
followed by /vis/drawVolume. Creating a new scene clears old contents and rebuilds the visual representation from the current geometry. If you change the geometry and rerun without recreating the scene, you might still see an old version.
Geant4 allows you to control drawing style, such as wireframe or solid, from macro commands. For instance, you can select a surface style before drawing:
/vis/viewer/set/style wireframe
and then call /vis/drawVolume to see only outlines of shapes. This is especially helpful when checking for overlaps and relative positions.
You can also selectively draw only the world volume or only volumes with a particular attribute, using commands in the /vis/filtering/ family combined with /vis/drawVolume. While these commands are more advanced, the pattern remains the same: configure what you want to see, then issue /vis/drawVolume to render it.
Whenever the geometry looks wrong or parts are missing, first confirm that:
You have opened a viewer, initialized visualization, created a scene, and called /vis/drawVolume after the geometry has been constructed.
If any of these steps are skipped, the viewer may open but the geometry will not be drawn, which can be confusing for beginners.
Views: 9