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Question G4 fail to find normal vector (only when a field is added) 

Forum: Geometry
Date: 18 May, 2016
From: <Loris>

Hello,

Here a problem I post in the Event and track managenement forum. Following the advice of Peter Grumplinger I'm posting here too. http://hypernews.slac.stanford.edu/HyperNews/geant4/get/eventtrackmanage/1309.html?inline=-1

" When I add a field throught ConstructSDandField() I get the following warning message each time a particle (neutron) is reflected on a volume (if I remove the field, the message disappear).

G4WT1 >   666 2.28e+03      357 -1.82e+03  1.19e-13        0       10  6.64e+03       World StepLimiter
G4WT1 >   667 2.29e+03      356 -1.83e+03   1.2e-13        0       10  6.65e+03       World StepLimiter
G4WT1 >   668 2.29e+03      356 -1.84e+03  1.21e-13        0       10  6.66e+03       World StepLimiter
G4WT1 >   669  2.3e+03      355 -1.85e+03  1.22e-13        0       10  6.67e+03       World StepLimiter
G4WT1 >   670  2.3e+03      355 -1.86e+03  1.23e-13        0       10  6.68e+03       World StepLimiter
G4WT1 >   671  2.3e+03      354 -1.87e+03  1.24e-13        0       10  6.69e+03       World StepLimiter
G4WT1 >   672 2.31e+03      354 -1.88e+03  1.25e-13        0       10   6.7e+03       World StepLimiter
G4WT1 > History depth=1
G4WT1 > 
-------- WWWW ------- G4Exception-START -------- WWWW -------
*** G4Exception : GeomNav0003
      issued by : G4Navigator::GetGlobalExitNormal()
 WARNING> Expected normal-global-frame to be valid,  i.e. a unit vector!
  - but |normal|   = 0  - and |normal|^2 = 0
 which differs from 1.0 by -1
   n = (0,0,0)
============================================================
   State of Navigator: 
The current state of G4Navigator is: 
  ValidExitNormal= 0
  ExitNormal     = (0,0,0)
  Exiting        = 0
  Entering       = 0
  BlockedPhysicalVolume= None
  BlockedReplicaNo     = -1
  LastStepWasZero      = 0

 Current Localpoint = (2309.5683,353.87294,-1881.6664)
 PreviousSftOrigin  = (2308.4242,354.00051,-1879.1911)
 PreviousSafety     = 2.4179583
Current History: 
Level=[0]: Phys Name=[World] Type=[N]
Level=[1]: Phys Name=[sphere_physical] Type=[N]

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

*** This is just a warning message. *** -------- WWWW -------- G4Exception-END --------- WWWW -------

G4WT1 >   673 2.31e+03      354 -1.88e+03  1.25e-13        0     2.73   6.7e+03 sphere_physical Transportation
G4WT1 >   674 2.31e+03      354 -1.88e+03  1.25e-13        0        0   6.7e+03       World Transportation
G4WT1 >   675  2.3e+03      351 -1.88e+03  1.25e-13        0       10  6.71e+03       World StepLimiter
G4WT1 >   676 2.29e+03      349 -1.88e+03  1.24e-13        0       10  6.72e+03       World StepLimiter
G4WT1 >   677 2.28e+03      346 -1.88e+03  1.24e-13        0       10  6.73e+03       World StepLimiter

(Here the geometry is just a sphere)

I have no idea where it comes from and if there is serious consequences on the reflection ?"

On Thu, 12 May 2016 21:34:59 GMT, Gumplinger Peter wrote:

> I don't know what it has to do with whether or not a field is present.
> In any case, it does recalculate a normal:
> 
> http://www-geant4.kek.jp/lxr/source/geometry/navigation/src/G4Navigator.cc#L1621

Yes but if it failed on time it may fail again. But it would be nice if this warning message could disappeared.

Thanks

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