KAHIBARO
9.1. Enabling Visualization
Table of Contents
Interactive visualization
To see the geometry of your GATE simulation, you need to enable visualization in Geant4 through OpenGATE. Visualization uses a graphics “driver” that draws volumes and, optionally, particle tracks. In practice, you will choose an interactive driver so that you can rotate, zoom, and inspect your setup while developing and debugging.
In OpenGATE, visualization is controlled when you create and configure the simulation object, before you start the run. You typically enable it with a flag or by selecting a visualization engine. Internally, OpenGATE configures the Geant4 visualization manager and opens a graphics window when you start the simulation in interactive mode.
Most systems rely on an OpenGL based driver for interactive work. If your environment has no display, for example when running on a remote server without a graphical session, you will not be able to use interactive visualization and should fall back to batch or file based methods described in other parts of this chapter. For your first tests on a laptop or workstation, make sure you run in a session with a working X or desktop environment so the visualization window can open.
Once visualization is enabled, starting the simulation will bring up a window that shows the world volume and any daughter volumes that are currently defined. The display will usually update when geometry is closed and the run is initialized. You interact with the view using the mouse and keyboard. Typical actions are rotation, panning, and zooming; most visualization windows show on screen hints or menu items for these operations.
Visualization is not required to run a simulation, but it is extremely valuable while you are building geometry. It helps you verify that volumes are present, correctly sized, and sensibly placed before you spend time on long runs.
Interactive visualization must be enabled and configured before starting the simulation. After the run is initialized, you cannot retroactively turn on visualization for that process.
Remember that visualization can slow down the start of a run, because the system has to build a graphical representation of all volumes. For large voxelized or highly repeated geometries, consider enabling visualization only during development and disabling it for production runs.
Viewing simulation geometry
With interactive visualization enabled, the main purpose is to inspect the geometry that you defined with your Python script. The visualization window shows a 3D view of the current geometry hierarchy starting from the world volume. Typically, the world appears as a wireframe box or is hidden, and your detectors, phantoms, and sources are drawn as solid or semi transparent shapes.
The default view might not immediately show all volumes, especially if your geometry is small compared to a very large world. Use the available controls to center and scale the scene so that your regions of interest are visible. Rotating the camera lets you check positions along different axes. Zooming helps you inspect small details, such as thin collimator septa or small detector crystals. Panning allows you to move the viewpoint without changing the viewing angle.
Most visualization systems let you toggle visibility of individual logical volumes or entire regions. For example, you can hide the world to avoid visual clutter, or hide shielding to look inside a scanner. Colors and transparency are usually taken from the properties you assign to volumes in your script. By giving different parts of your geometry distinct colors, you make it easier to see boundaries and relationships between components.
When you view the geometry, pay attention to the following: volumes should appear inside their intended parent volumes, not outside; detector arrays should show a regular pattern with the correct spacing; phantoms and patients should be centered and oriented as expected. If anything looks wrong, correct the corresponding part of your geometry definition and reinitialize the visualization.
Some visualization drivers also allow you to overlay particle tracks, but the details of track display are covered in another chapter about visualizing particle tracks. For geometry inspection, it is usually best to look at the static volumes first, without tracks, to clearly see shapes and placements.
Always visually inspect new or modified geometries before running long simulations. A quick look at the geometry can reveal misplaced volumes, wrong orientations, or missing components that are hard to detect from numerical output alone.
Viewing the geometry interactively is one of the most effective ways to debug your setup. Combined with tools for overlap checks and detailed geometry reports described elsewhere, visualization helps you move from an abstract description in code to a concrete, validated 3D setup that reflects your intended scanner, phantom, or patient configuration.
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