11. The Belle II Event Display#

See also

evdisp.belle2.org for a live event display of the data-taking in real time.

../../_images/Belle2EventDisplay.png

Fig. 11.1 A pretty view of the tracking detectors of Belle II. This picture was created with the event display (so no excuses for ugly low-resolution screenshots).#

See also

Here is a gallery of nice event display images.

11.1. Starting the display#

The Belle II event display is invoked with b2display. You can use it to explore any Belle II File Format files.

You must use a full release, and it is usually recommended to use the same release that was used to create the file you want to explore. If you are working remotely, you will need to connect with xforwarding or start a vncserver (if permitted by your institute).

$ b2setup <any release>
$ b2file-metadata-show /path/to/your/mdst.root
$ # read the metadata and find the release number
$ b2setup release-xx-yy-zz
$ b2display /path/to/your/mdst.root

See also

Choosing a release

11.1.1. b2display: Run the event display (opens an xwindow)#

Usage:

b2display input_file.root

Show data in given input file using the event display.

You can also open multiple files using wildcards, though you have to pass the string with wildcards to b2display to prevent expansion by the shell, e.g.

b2display "my/files/mdst_*.root".

Using .sroot files, and http:// or root:// URLs is also possible.

Configuration of the display can be changed from the defaults by editing display/examples/display.py. See output of basf2 -m Display for available options.

11.2. Viewer navigation and the user interface#

The right side shows a 3D view (top) and ρ-z and r-ϕ projections (bottom left/right). The views can be navigated by clicking in one (to choose) then by holding the left, middle or right mouse button and moving the cursor, the scroll wheel will also work.

Here are all of the mouse and keyboard bindings:

Page Down

Go to next event

Page Up

Go to previous event

Space

Toggle automatic event advancing (e.g for online display)

s

Save As (with high resolution)

Ctrl+q

Quit

Left drag

Rotate

Right drag

Dolly (move camera along view axis)

Middle drag

Move view

Mouse wheel

Zoom

Arrow keys

Move view

Ctrl

Slower (combine with arrow keys or mouse actions)

Ctrl+Shift

Even slower (combine with arrow keys or mouse actions)

Shift

Faster (combine with arrow keys or mouse actions)

r

Normal rendering

w

Wireframe rendering

t

Hybrid rendering (normal + wireframe)

d

OpenGL debug mode (shows reference points & box)

j/k

Dolly (move camera along view axis)

The left side of the window shows two tabs: the Event Control tab visible after starting the display allows you to switch between events in the loaded file and shows event/run/experiment numbers. The Delay field and play/stop button allow you to automatically advance to the next event after the specified delay (in seconds).

../../_images/event_tab.png

Fig. 11.2 The Event Control tab on the left-hand panel.#

The Options box allows changing some of the options also available as module parameters at runtime. Most importantly, you can select which parts of an event should be shown: MC info, track candidates, and/or reconstructed tracks (and related objects).

You can also save images of the currently active viewer (selected by clicking anywhere in it) using Save As…. Support for exporting vector graphics is fairly limited, most likely you should save them as .png files. The Save As (High-Res)… button creates a high resolution image. (Specifying very high resolutions may crash your X server, 4000px should be fine). If you want to print them later, you should probably also change the background colour using the Dark/light colors button.

Important

We recommend saving high resolution if you intend to show these anywhere outside of the collaboration.

The Eve tab shows a tree representation of all objects displayed, including geometry and event data, as well as the different projections and viewers. Every one of them can be enabled/disabled using the check box in front of the name, and many can also be changed. For example, the ‘Viewers’ can be modified to e.g. show only half of the detector (clipping) or save .gifs showing rotations.

../../_images/eve_tab.png

Fig. 11.3 The Eve tab on the left-hand panel.#

It is often useful to disable the geometry if you want to look at some tracks in detail, which can be done by removing the check mark in front of ‘Geometry scene’. Conversely, you can also enable a more detailed geometry for the 3D view by enabling the ‘Top’ node. For the track collections (called ‘MCParticles’ and ‘Fitted tracks’), you can also control which sub-items to show using the provided p/pT sliders. For individual MCParticles/GFtracks, you can show additional information like its array index, p/pT, mother particles or pValue by hovering the mouse pointer over the track in the tree, or also in the viewer directly (works best in projections).

11.3. Visualised objects#

Geometry

By default, a simplified geometry is shown. See the last paragraph for instructions on how to disable it or show the full geometry instead. The default can be changed using the fullGeometry module parameter. With the full geometry shown, you can also set the level of detail by changing the VisLevel setting of Eve tab → ‘Geometry scene’ → ‘Top’ (then you should see it in the bottom panel). The default value of VisLevel will e.g. hide most of the KLM structure, which might be interesting to you.

MC info (MCParticles, SimHits)

MCParticles are coloured depending on their PDG value (pions in gray, kaons in red, electrons in blue, muons in cyan, protons in yellow, photons in bright green and others in magenta), SimHits share the colour of their parent particle. By enabling the Assign hits to primaries option, you can hide particles generated by Geant4 and have hits instead assigned to their primary mother particles.

By default, only particles that produced hits in the detector are shown, with the exception of primary particles. This can be changed using the Show all primaries, Show all charged and Show all neutrals options.

MCParticles shown as dashed lines use only their starting position and momentum plus creation vertices of any secondaries, and may thus be wildly inaccurate. If the trajectoryStore parameter of FullSim is used (e.g. set to 2), the real trajectories are plotted and MCParticles are shown as solid lines.

Track candidates & reconstructed hits

This shows track candidates produced by track finders with their associated hits in light blue, as well as reconstructed hits in the tracking detectors not assigned to a track candidate (in violet). Supported hits are PXDClusters, SVDClusters, and CDCHits. If the useClusters parameter is set to False, PXDTrueHits and SVDTrueHits will be shown instead of clusters.

Tracks, vertices, clusters

Fitted tracks are shown as lines between green points generated using genfit’s track extrapolation, the reco hits are shown as well in yellow, for the CDC as tiny drift cylinders. GFRaveVertex objects are shown as yellow error ellipsoids, plus a dot in the center (for increased visibility). ECLClusters are red blocks representing energy – if MC info is shown, they should overlap with the MC photons (thin green lines).

11.4. Window management#

Eve allows some advanced window management operations. To access them, expand the small green bar above the view you want to modify by clicking on it.

The Actions menu then gives you access to different operations. All important ones are found at the very top:

  • SwapWindowWithCurrent swaps this view with the currently selected view, which is selected by anywhere in it.

  • UndockWindow moves this view into its own window, so it can be freely moved around, or shown in fullscreen.

  • DestroyWindow removes this view entirely until the display is restarted.

11.5. Troubleshooting#

Unfortunately, the event display is a bit susceptible to xforwarding problems and graphics driver issues (on both the local and remote machines). Please report bugs and ask questions if you encounter problems (tag them with “b2display”).

Here are some common issues:

  • OpenGL errors, e.g. “GL Error invalid operation” indicate problems with your video drivers. Try upgrading your drivers (On Ubuntu, try jockey-text -l to list available drivers.)

  • On some systems with intel GPUs, as well as on VirtualBox, the accelerated drivers may produce crashes (you’ll see a stack trace ending in, e.g., i965_dri.so). Setting export LIBGL_ALWAYS_SOFTWARE=1 before starting the display may help.

  • VMWare VMs also suffer from the same problem, but the workaround (see last point) doesn’t help there. VirtualBox seems to be more suitable here (it also supports reading hard disk images created by VMWare).

  • Mac is sometimes particularly problematic. You need to install Xquartz and enable iglx. defaults write org.macosforge.xquartz.X11 enable_iglx -bool true

See also

CMS have a helpful twiki page listing some further things that might go wrong.

See also

Questions tagged with b2display on questions.belle2.org.

11.6. Module documentation#

The display package contains two important modules. Here is their full module documentation.

AsyncDisplay#

Starts the Display module asynchronously (with buffered input). Note that the buffer is limited in size and not all events can be passed to the display once it is full. (Configurable using ‘discardOldEvents’ param).

Package

display

Library

libdisplay.so

Parameters
  • assignHitsToPrimaries (bool, default=False)

    If true, hits created by secondary particles (after scattering, decay-in-flight, …) will be assigned to the original primary particle.

  • automatic (bool, default=False)

    Non-interactively save visualisations for each event. Note that this still requires an X server, but you can use the ‘Xvfb’ dummy server by running basf2 using ‘xvfb-run -s “-screen 0 640x480x24” basf2 …’ to run headless.

  • customGeometryExtractPath (str, default=’’)

    Path to custom file with geometry extract.

  • deleteVolumes (list(str), default=[])

    List of volumes to be deleted. The volume and all its daughters will be deleted completely. Uses Regular Expressions (RE)! If the expression starts with ‘#’, only daughters are removed (# is removed for RE)

  • discardOldEvents (bool, default=True)

    Discard old events when buffer is full. If false, the main process will wait until there is enough space in the buffer. (i.e. synchronous operation)

  • fullGeometry (bool, default=False)

    Show full geometry instead of simplified shapes. Further details can be enabled by changing the VisLevel option for Eve -> Scenes -> Geometry Scene -> Top_1.

  • hideObjects (list(str), default=[])

    Objects which are to be hidden (can be manually re-enabled in tree view). Names correspond to the object names in the ‘Event’. (Note that this won’t work for objects somewhere deep in the tree, only for those immediately below ‘Event’.)

  • hideSecondaries (bool, default=False)

    If true, secondary MCParticles (and hits created by them) will not be shown.

  • hideVolumes (list(str), default=[])

    List of volumes to be hidden (can be re-enabled in Eve panel / Geometry scene. The volume and all its daughters will be hidden.

  • options (str, default=’MH’)

    Drawing options for RecoTracks, a combination of DHMP. See EVEVisualization::setOptions or the display.py example for an explanation.

  • playOnStartup (bool, default=False)

    When launching the event display, immediately start advancing through events. Useful for control room uses etc.

  • showARICHHits (bool, default=False)

    If true, ARICHHit objects will be shown.

  • showAllPrimaries (bool, default=True)

    If true, all primary MCParticles will be shown, regardless of wether hits are produced.

  • showCDCHits (bool, default=False)

    If true, CDCHit objects will be shown as drift cylinders (shortened, z position set to zero).

  • showCharged (bool, default=True)

    If true, all charged MCParticles will be shown, including secondaries (implies disabled assignHitsToPrimaries). May be slow.

  • showKLM2dHits (bool, default=True)

    If true, KLMHit2d objects will be shown in the display.

  • showMCInfo (bool, default=True)

    Show Monte Carlo information (MCParticles, SimHits)

  • showNeutrals (bool, default=True)

    If true, all neutral MCParticles will be shown, including secondaries (implies disabled assignHitsToPrimaries). May be slow.

  • showRecoTracks (bool, default=False)

    If true, track candidates (RecoTracks) and reconstructed hits will be shown in the display.

  • showTrackLevelObjects (bool, default=True)

    If true, fitted Tracks, GFRave Vertices and ECLCluster objects will be shown in the display.

  • showTriggerObjects (bool, default=False)

    If true, CDCHit objects will be assigned to trigger segments and trigger tracks will be shown.

Display#

Interactive visualisation of Monte Carlo, intermediate and reconstructed objects, plus geometry. See https://confluence.desy.de/display/BI/Software+/EventDisplay for detailed documentation.

Package

display

Library

libdisplay.so

Parameters
  • assignHitsToPrimaries (bool, default=False)

    If true, hits created by secondary particles (after scattering, decay-in-flight, …) will be assigned to the original primary particle.

  • automatic (bool, default=False)

    Non-interactively save visualisations for each event. Note that this still requires an X server, but you can use the ‘Xvfb’ dummy server by running basf2 using ‘xvfb-run -s “-screen 0 640x480x24” basf2 …’ to run headless.

  • customGeometryExtractPath (str, default=’’)

    Path to custom file with geometry extract.

  • deleteVolumes (list(str), default=[])

    List of volumes to be deleted. The volume and all its daughters will be deleted completely. Uses Regular Expressions (RE)! If the expression starts with ‘#’, only daughters are removed (# is removed for RE)

  • fullGeometry (bool, default=False)

    Show full geometry instead of simplified shapes. Further details can be enabled by changing the VisLevel option for Eve -> Scenes -> Geometry Scene -> Top_1.

  • hideObjects (list(str), default=[])

    Objects which are to be hidden (can be manually re-enabled in tree view). Names correspond to the object names in the ‘Event’. (Note that this won’t work for objects somewhere deep in the tree, only for those immediately below ‘Event’.)

  • hideSecondaries (bool, default=False)

    If true, secondary MCParticles (and hits created by them) will not be shown.

  • hideVolumes (list(str), default=[])

    List of volumes to be hidden (can be re-enabled in Eve panel / Geometry scene. The volume and all its daughters will be hidden.

  • options (str, default=’MH’)

    Drawing options for RecoTracks, a combination of DHMP. See EVEVisualization::setOptions or the display.py example for an explanation.

  • playOnStartup (bool, default=False)

    When launching the event display, immediately start advancing through events. Useful for control room uses etc.

  • showARICHHits (bool, default=False)

    If true, ARICHHit objects will be shown.

  • showAllPrimaries (bool, default=True)

    If true, all primary MCParticles will be shown, regardless of wether hits are produced.

  • showCDCHits (bool, default=False)

    If true, CDCHit objects will be shown as drift cylinders (shortened, z position set to zero).

  • showCharged (bool, default=True)

    If true, all charged MCParticles will be shown, including secondaries (implies disabled assignHitsToPrimaries). May be slow.

  • showKLM2dHits (bool, default=True)

    If true, KLMHit2d objects will be shown in the display.

  • showMCInfo (bool, default=True)

    Show Monte Carlo information (MCParticles, SimHits)

  • showNeutrals (bool, default=True)

    If true, all neutral MCParticles will be shown, including secondaries (implies disabled assignHitsToPrimaries). May be slow.

  • showRecoTracks (bool, default=False)

    If true, track candidates (RecoTracks) and reconstructed hits will be shown in the display.

  • showTrackLevelObjects (bool, default=True)

    If true, fitted Tracks, GFRave Vertices and ECLCluster objects will be shown in the display.

  • showTriggerObjects (bool, default=False)

    If true, CDCHit objects will be assigned to trigger segments and trigger tracks will be shown.