Volumetric calculation issue

[valeriaRaffuzzi]

Problems with rayVolPP

• vacuum boundary conditions have to added to trackRay
• should change the robust check to the collision point (?)
• NUDGE in cellUniverse is a bit dodgy and might cause troubles.

[Mikolaj-A-Kowalski]

Regarding the NUDGE I think #7 is probably related... The nudging in cellUniverse makes it move around a little bot on the order of 1.0e-8 which is sufficient to to erroneously choose a surface hit on a lower universe level.

[vitmog]

Such kind problems usually exist due to conflict between an exactly defined particle discrete state regarding to a surface (sign & cell & material) and approximately known floating-point coordinates of the particle. The only resolution of the conflict consists in choosing the discrete state as dominative over the coordinates state. Good explanation of an example of a correct tracing algorithm is given in Beliajew starting from page 108.