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Warning Inifinite loop in G4OpBounadryProcess::DoReflection() 

Forum: Processes Involving Optical Photons
Date: 13 Apr, 2009
From: Maxim Gonchar <Maxim Gonchar>

Hi,

Sometimes Geant4 fails to calculate a surface normal. 
In this case it sets the flag "valid" to false and 
G4OpBounadryProcess prints an error message, but 
continues to work.
The problem is in G4LambertianRand(G4ThreeVector* normal) 
which falls into the infinite loop when argument is (0.,0.,0.).

I think that the magnitude of a surface normal should be checked 
before calling G4LambertianRand. But what happens to the 
Lambertian reflection in case when the normal is 0? What should 
be used instead?  

PS. Code to get normal=(0., 0., 0.):
    G4Tubs* blk = new G4Tubs("blk",2.249740e+03, 
                                   2.252740e+03,
                                   4.990000e02,
                                   0.000000e+00,
                                   2.609116e-01);
    G4ThreeVector localpoint(-1.59250955522304866463e+03,              
                              1.60239571861107833683e+03, 
                              1.55565646370305239543e+03);
    G4ThreeVector dir(-2.97231637897997502673e-01, 
                      -9.46902667985754731284e-01, 
                      -1.22591560859357129321e-01);
    bool valid;
    G4ThreeVector norm;
    double dist=blk->DistanceToOut(localpoint, dir, true, &valid, &norm);
    printf("dist=%20f, norm(%20f, %20f, %20f), valid=%i\n",
            dist,norm.x(),norm.y(),norm.z(),valid);

best regards, Maxim Gonchar

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1 Feedback: Re: Inifinite loop in G4OpBounadryProcess::DoReflection()   (Gumplinger Peter - 06 May, 2009)
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