How can I store the global time for each step of a trajectory in a HepRep file?

Recording, Visualizing and Persisting Data
1

Dear Geant4 experts,
How can I store the global time for each step of a trajectory in a HepRep file? I see that the positions of the steps are saved and some information about the trajectory when I use “/vis/scene/add/trajectories rich”. Also there is the possibility to add attributes but I don’t see how to do this for a step.

Thanks in advance,
Dittmar

2

Hi Dittmar

If you use /vis/scene/add/trajectories rich you get attributes as shown below (you should see this printing, but maybe you need /vis/verbose confirmations too). So global time is available for each step of the trajectory. (If you are in a magnetic field, you may miss some steps unless you /vis/scene/add/trajectories smooth rich.)

So global time should be available in HepRepFile (not HepRep nor HepRepXML). HepRepFile output is browsable with HepRApp - see documentation. The global time is certainly available to trajectory filtering commands and is used in “time slicing” - see documentation.

If you wish to add your own attributes, it can be done. It’s quite tricky so get back to me on that one.

Good luck
John

G4TrajectoriesModel:
  Event ID (EventID): G4int
  Run ID (RunID): G4int
G4RichTrajectory:
  Creator Model ID (CMID): G4int
  Creator Model Name (CMN): G4String
  Creator Process Name (CPN): G4String
  Creator Process Type Name (CPTN): G4String
  Charge (Ch): unit: e+ (G4double)
  Ending Process Name (EPN): G4String
  Ending Process Type Name (EPTN): G4String
  Final kinetic energy (FKE): G4BestUnit (G4double)
  Final Next Volume Path (FNVPath): G4String
  Final Volume Path (FVPath): G4String
  Track ID (ID): G4int
  Initial kinetic energy (IKE): G4BestUnit (G4double)
  Initial momentum magnitude (IMag): G4BestUnit (G4double)
  Initial momentum (IMom): G4BestUnit (G4ThreeVector)
  Initial Next Volume Path (INVPath): G4String
  Initial Volume Path (IVPath): G4String
  No. of points (NTP): G4int
  PDG Encoding (PDG): G4int
  Parent ID (PID): G4int
  Particle Name (PN): G4String
G4RichTrajectoryPoint:
  Auxiliary Point Position (Aux): G4BestUnit (G4ThreeVector)
  Process Defined Step (PDS): G4String
  Process Type Defined Step (PTDS): G4String
  Position (Pos): G4BestUnit (G4ThreeVector)
  Post-step-point status (PostStatus): G4String
  Post-step-point global time (PostT): G4BestUnit (G4double)
  Post-step Volume Path (PostVPath): G4String
  Post-step-point weight (PostW): G4double
  Pre-step-point status (PreStatus): G4String
  Pre-step-point global time (PreT): G4BestUnit (G4double)
  Pre-step Volume Path (PreVPath): G4String
  Pre-step-point weight (PreW): G4double
  Remaining Energy (RE): G4BestUnit (G4double)
  Total Energy Deposit (TED): G4BestUnit (G4double)
3

Hello John,
Thank you very much for your answer. I don’t quite understand how I can save the global time for each step in a HepRep file by applying filters. I can filter by charge and plot/save a specific one but how do I do that with the global time? I don’t want to filter out a trajectory just save the time in addition to the location. Could you tell me what commands to use or where to find them?

Thanks in advance,
Clemens

4

Hi Clemens

Maybe using trajectory attributes is not the way to go for you.

You can intercept every step in your stepping action. Even examples/basic/B1 has a stepping action. At each step you can get everything that Geant4 has to offer. Have a look at Tracks and steps — FrequentlyAskedQuestions 11.0 documentation.

John

5

Hello John,
I basically just need an xml or txt file with x,y,z position, time, type of particle and its energy. It needs to be a file as I will then pass it on to another programme running on a different operating system. There the event should be visualized in a slow motion sequence. For this visualization I need a simple xml or txt file. I had hoped that the HepRep format might offer this directly.
Could I ask you if you know of an example where such information is stored in an xml or txt format?
With kind regards
Clemens

6

Hi Clemens

Have you had a look at Making a Movie — Book For Application Developers 11.0 documentation? In particular, Using /vis/viewer/interpolate? Have a look at examples/extended/visualization/movies.

If you want to do it yourself, making a file as you propose can get quite tricky, especially in multithreaded mode. Come back to me on that one.

John

7

Hello John,
I have found a suitable solution for me. Using these three commands in vis.mac, the global time per step for each particle is also stored in a HepRep file.

/vis/scene/add/trajectories rich
/vis/modeling/trajectories/create/drawByParticleID
/vis/modeling/trajectories/drawByParticleID-0/default/setDrawStepPts true

Thank you very much for your help,
Clemens

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