GDML Tessellated Faces

Geometry, Fields and Transportation
1

It has come to my attention that for a STL file, if one looks at at the outward side of an face the order of the vertices should be in counterclock-wise order (right-hand-rule)

Is this also a requirement for a GDML Tessellated Object?

2

Yes, the vertices in G4TriangularFacet and G4QuadrangularFacet should be defined in counterclockwise order.

3

Thanks. Are there any Geant4 facilities for tracking down a problem with an invalid Tessellated Object?

4

I assume that by “invalid Tessellated Object” you mean a tessellated object that either:

  • has wrong orientation of faces
    or
  • is not closed (contains holes)

G4TessellatedSolid itself does not check correctness of its structure.
Orientation of faces can be checked by calculation of volume, it should be positive.

If a tessellated object is closed, then every edge should belong to two faces. Such check is performed at creation of a polyhedron object:

polyhedron->SetReferences();

5

Seeing this exception

------ Exception----
============================================================
   State of Navigator:
The current state of G4Navigator is:
  ValidExitNormal= 152
  ExitNormal     = (0,0,0)
  Exiting        = 1
  Entering       = 0
  BlockedPhysicalVolume= None
  BlockedReplicaNo     = -1
  LastStepWasZero      = 1

 Current Localpoint = (-1e-07,0.895,2.8327694e-23)
 PreviousSftOrigin  = (0,0,0.1800001)
 PreviousSafety     = 0
Current History:
History depth=1
Level=[0]: Phys Name=[worldVOL_PV] Type=[N]
Level=[1]: Phys Name=[Part] Type=[N]

============================================================
Value obtained from stored global-normal is not a unit vector.

WorldVol_PV contains a World Volume GDMLBox Object and Part contains a GDMLTessellated Object
and we are not understanding the exception.

6

The exception reports that the normal obtained by the navigator is not a unit vector. Indeed, ExitNormal = (0,0,0). The reason why this happened requires investigation, it could be a bug in G4TessellatedSolid or in the navigator itself.

7

Any suggestions on how to proceed / progress?

8

Difficult to advise. Ideally, it would be nice to have a small test case that reproduces the problem.