GEARS 齿轮组

Visualization of detector geometry

The visualization chapter of the Geant4 Book For Application Developers documents in detail how to visualize a detector using various tools.

ASCIITree

The ASCIITree visualization driver does not really visualize anything. Instead, it prints a hierarchical list of volumes in a detector in a terminal. If your geometry is simple, the only two commands you need in your macro is:

/vis/ASCIITree/verbose 13
/vis/drawTree

If your geometry is complicated, you can specify the volume to be printed following the instruction here.

A sample ASCIITree macro is shipped with GEARS. Try it out this way in Linux or macOS:

$ cd /path/to/gears
$ cd tutorials/detector/visualization
$ gears ASCIITree.mac

Follow this instruction to try it out in Windows.

RayTracer

The RayTracer visualization driver is included in any Geant4 installation, and can be used for geometries that other tools may fail to visualize. Detailed instructions on RayTracer related built-in commands can be found here.

A sample RayTracer macro is shipped with GEARS. Try it out this way:

$ cd /path/to/gears
$ cd tutorials/detector/visualization
$ gears RayTracer.mac

It generates a g4RayTracer.viewer-0_0000.jpeg file in the same directory. Note that the working principle of RayTracer is to shoot many rays (360000 by default) through the detector geometry and draw their intersecting points to reveal the geometry surfaces. Because of this, it takes more time than other methods to finish. It cannot be used to show particle trajectories, the world geometry, nor any cross section. Its advantage is to show complex geometry that other visualization method may fail.

VRML

The VRML visualization driver is available in any Geant4 installation. It is used to generate files in VRML format, which can be viewed using an external program, such as ORBISNAP, FreeWRL (handy for MacOS), OpenVRML, view3dscene (only for Linux and Windows), 3D builder (default Windows 10 App), etc., or be converted to its succeeder X3D, which can be viewed directly in a modern web browser that supports WebGL.

A sample VRML macro is shipped with GEARS. Try it out this way:

$ cd /path/to/gears
$ cd tutorials/detector/visualization
$ gears VRML.mac

It generates g4_??.wrl in the same directory.

A shell script v2x is shipped in the same directory to convert the latest g4_??.wrl to g4_??.x3d, embed the latter to g4_??.html and run a simple http server using python3 in the current directory. Open http://127.0.0.1:8000/g4_??.html in a modern browser to see the result.

The last service defined in gears/docker-compose.yml x3d serves a website in a Docker container to visualize g4_??.html.

HepRepFile

The HepRepFile visualization driver is available in any Geant4 installation. It can be used to generate G4Data*.heprep files, which can be viewed using an external program called HepRApp in wireframe mode, that is, no surface, only outlines, which sounds primitive, but is one of the best ways to troubleshoot a complicated geometry.

A sample HepRepFile macro is shipped with GEARS. Try it out this way:

$ cd /path/to/gears
$ cd tutorials/detector/visualization
$ gears HepRepFile.mac

It generates G4Data0.heprep in the same directory. A shell script hv is shipped with GEARS to run HepRApp. Use it this way:

$ ./hv G4Data0.heprep

If this is the first time you run it, it will download a HepRApp.jar file from the Internet and run it the following way:

java -jar HepRApp.jar -opt HepRApp.properties -file G4Data0.heprep

In case of Windows, please download HepRApp.jar and double click on it in a file browser to launch it instead of usimng the command above.

Unfortunately, HepRApp.jar can only be run on java version 1.8 (or 8 in short). To use the HepRApp viewer, you may need to install two versions of java and switch to the older one if needed. This can be done, but the detailed procedure changes with the OS. In case of Windows, simply download java 8 from https://www.java.com/en/download. In case of modern MacOS or Linux distributions, there is no tested working procedure. A Docker image https://hub.docker.com/r/physino/heprapp is create to solve this problem. It can be used in the following way:

download and run Docker Desktop
for Mac and Windows users: run an X11 server (XQuartz for Mac, MobaXterm for Windows)
for Mac and Linux users: run xhost + in a terminal
download GEARS, and then

cd /path/to/gears
docker-compose run heprapp

The HepRApp window should pop up on your desktop.

Dockerfile shows how the Docker image is created. HepRApp.def shows how the Apptainer image is created.

HepRApp.properties is the configuration file for HepRApp. It is also shipped with GEARS.

In HepRApp browser, “beam view” is to look at -z direction, “top view” is to look at -y direction, and “side view” is to look at +x direction.

TSG

ToolsSG is available in Geant4 version >= 11.1. It can be used with X11 or Qt.

A sample ToolsSG macro is shipped with GEARS. Try it out this way:

$ cd /path/to/gears
$ cd tutorials/detector/visualization
$ gears
$ /control/execute TSG.mac

DAWNFILE

DAWNFILE is available in any Geant4 installation. It can be used to generate g4_*.prim files, which can be converted to an EPS file using an external program called dawn.

A sample DAWNFILE macro is shipped with GEARS. Try it out this way:

$ cd /path/to/gears
$ cd tutorials/detector/visualization
$ gears DAWN.mac

OpenGL

OpenGL is included in most Geant4 installations. Detailed instructions on OpenGL related built-in commands can be found here

A sample OpenGL macro is shipped with GEARS. Try it out this way:

$ cd /path/to/gears
$ cd tutorials/detector/visualization
$ gears OpenGL.mac

It generates a gears_????.pdf file in the same directory.

Note that even if you run it in batch mode, the Geant4 UI session must be set to Qt instead of tcsh. Otherwise OpenGL won’t work. It can also be run in the interactive mode, where you can use your mouse to rotate the visualized geometry.

For Mac users, you may need to run

defaults write org.macosforge.xquartz.X11 enable_iglx -bool true

in a terminal to enable iglx for XQuartz if you encounter the following error message when running gears OpenGL.mac:

libGL error: No matching fbConfigs or visuals found
libGL error: failed to load driver: swrast
X Error ...

References:

Visualization of particle trajectories

Most of the visualization methods can be used to visualize not only the detector geometry but also particle trajectories passing through it. This is enabled using the following command

/vis/scene/add/trajectories

Note This may slow down your visualization program or enlarge its output file if many particles are created in a simulation.

The scene will be cleared after each event. In case of HepRepFile, ten G4Data*.heprep files will be created if you run /run/beamOn 10, each contains the scene of one event. If you want to overlap the results from multiple events in one scene, use

/vis/scene/add/trajectories
# accumulate trajectories from 10 events
/vis/scene/endOfEventAction accumulate 10

Only one G4Data01.heprep will be created in this case if you use HepRepFile.

More information can be saved with trajectories with the following syntax:

/vis/scene/add/trajectories rich

By default, green tracks are neutral particles, e.g. gamma-rays; red tracks are negatively charged particles, e.g. electrons; blue tracks are positively charged particles, e.g. protons. But these default settings can be changed, for example,

/vis/modeling/trajectories/create/drawByParticleID
/vis/modeling/trajectories/drawByParticleID-0/set e- blue

There are also ways to hide trajectories based on particle type:

/vis/filtering/trajectories/create/particleFilter
# draw only gamma-rays
/vis/filtering/trajectories/particleFilter-0/add gamma
# draw everything except for gamma-rays
/vis/filtering/trajectories/particleFilter-0/invert true

Visualization of axes, date, text, etc.

You can add more objects to a scene:

# Add x (red), y (green), z (blue) axes in the middle of the scene
/vis/scene/add/axes
# add date to the corner of the scene
/vis/scene/add/date
# add text to the scene
/vis/scene/add/text 2 3 4 m 12 0 0 hello

For more information please check the manual of /vis/scene/add/.

GEARS | 齿轮组

Geant4 Example Application with Rich features and Small footprints