Messages: Track stuck, not moving for 25 steps

Geometry, Fields and Transportation
1

Hi~
I constructed my model in GEANT4 via the gdml file, which is converted from a .stp file. However, I got the following messages when I run my program. I am not sure if it is caused by geometry errors. I have checked my .stp model and found it is okay. So I am wondering if someone can tell me the reason of these issues.
Besides, what influence would these messages make to my results? Thank you.

…
-------- EEEE ------- G4Exception-START -------- EEEE -------
*** G4Exception : GeomNav0003
issued by : G4Navigator::ComputeStep()
Stuck Track: potential geometry or navigation problem.
Track stuck, not moving for 25 steps
in volume -LV_VVport02-98_PV- at point (10672.4,887.587,-6569.55)
direction: (0.877659,-0.472255,-0.0817929).
*** Event Must Be Aborted ***
G4WT14 > G4Track (0x7f5db0c99d70) - track ID = 5, parent ID = 1
G4WT14 > Particle type : gamma - creator process : neutronInelastic, creator model : Undefined
G4WT14 > Kinetic energy : 941.076 keV - Momentum direction : (0.877659,-0.472255,-0.0817929)
G4WT14 > Step length : 1 Ang - total energy deposit : 0 eV
G4WT14 > Pre-step point : (10672.4,887.587,-6569.55) - Physical volume : LV_VVport02-98_PV (M105)
G4WT14 > - defined by : Transportation - step status : 1
G4WT14 > Post-step point : (10672.4,887.587,-6569.55) - Physical volume : LV_VVport02-98_PV (M105)
G4WT14 > - defined by : compt - step status : 7
G4WT14 > *** Note: Step information might not be properly updated.
G4WT14 >
-------- EEEE -------- G4Exception-END --------- EEEE -------
…

2

In my experience (with “hand-built” geometries, not STEP files), this is usually due to a very tight overlap between volumes (one volume’s edge is very slightly inside the boundary of the adjacent volume). It can be hard to debug just from the printed out coordinates. You should look at how the volumes of interest, and their neighbors, have been defined, and see if maybe there’s some adjustment you can make with dimensions.

3

Thank you very much, Michael.
I converted my STEP model to GDML file via a third-party program. I ever suspected the reason of those messages is model overlap. But I once checked one volume, which was reported “Stuck Track: potential geometry or navigation problem.”. That volume has 5 plane surface boundaries and 1 annulus surface boundary, but I cannot find any overlap surfaces of this volume in the STEP file.
My model is very complex. Is there a convenient and accurate way to import it into GEANT4?
Thank you and best regards,
jcren.