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Keywords: PCcone warnings
Forum: Particles
Re: None What is that? "Warning ... PCone not able to return normal .." (Dvorak)
Re: News Re: What is that? "Warning ... PCone not able to return normal .." (Igor Machulin)
Date: 03 Apr, 2003
From: Gumplinger Peter <Gumplinger Peter>

Hi Igor,

From your comments I am unclear as to whether the second call to get the surface normal, the one which generates the warning, happens immediately after the first call, or when the photon encounters the surface again some distance away.

Upon reflection of a photon on any surface, a tiny step is taken by the G4Navigator. This is a quirk of GEANT4 but the G4OpBoundaryProcess is written with this in mind. Therefore, you'll find this line in the PostStepDoIt:

        if (aTrack.GetStepLength()<=kCarTolerance/2)
                return G4VDiscreteProcess::PostStepDoIt(aTrack, aStep);

With other words, the DoIt should return and not spring back into action, at the end of this tiny intermediate step. If for some reason, this tiny step ends up to be larger than kCalTolerance/2 for the case of a G4BREPSolidPCone, then we've got a problem. I would think though that the problem would be more severe than just warning messages filling the screen.

If you were to print: aTrack.GetStepLength() in your version of the G4OpBoundaryProcess.cc code it would be interesting to see what step sizes are between calls to

        theLocalNormal = theNavigator->GetLocalExitNormal(&valid);

in G4OpBoundaryProcess::PostStepDoIt

Regards, Peter

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