Dear rooters, I am working now with the optical photon reflection in VMC with TGeant3. For the reflection, the normal to the reflecting surface is calculated by TGeant3::ggperp() which delegates this calculation to TGeoManager::FindNormalFast(). Apparently, this function returns the normal always (0,1,0) whatever the surface it is. In the comments to TGeant3.cxx it is written that before 2003/12/10 the normal was calculated via TGeoManager::FindNormal(). Returning to this old version gives more correct normal (I cannot say that is is absolutely correct, but it is better that (0,1,0)). Any clue? Thanks, Yuri Kharlov.
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