Re: ROOT & GEANT

From: Pasha Murat (murat@cdfsga.fnal.gov)
Date: Tue Feb 24 1998 - 23:50:15 MET


Alexander Zvyagin writes:
 > One problem stops me. I do not know how to insert correctly
 > in mother TNode several identical son-TNodes. This is GSPOS level of GEANT
 > calls. 
... snip ...
 > At present time I don not know how to solve the problem...
....
P.S. I hope that GEANT4 will solve a lot of problems ...
....


	Hello Alexander,

to the moment your problem doesn't have a solution. And this was exactly 
the major objection of mine against using ROOT TGeometry to initialize 
G3 geometry structure! G3 geometry description just has *more* degrees of freedom. 
But to the moment ROOT project doesn't pretend to have an equivalent of G3...

BTW, here is a possible suggestion for ROOT developers: if we forget about 
G3 geometry description not having a concept of *surface*, in all other 
respects it seems to be pretty well designed. What about translating it into 
C++ and implementing in ROOT? (Yes, we at CDF have done something like this 
already, but I wouldn't be surprised if it is possible to do it better 
than we did...)

One could consider, for example, the following hierarchy:

TShape <---- TVolume <--- TBRIK

(all classes in the chain are derived from each other)

with TShape corresponding to G3 CALL GSVOLU, TVolume corresponding to CALL GSPOS,
but still being a generic class and TBRIK etc being user-visible classes ?

This 

1. shouldn't break anything in ROOT geometry classes (small cosmetical changes 
   are required though)
2. would allow a straightforward way of interfacing to G3 and, in particular,
   would solve the problem you are having;
3. could provide a good starting point for looking around and thinking about 
   what the next right step should be.


			Comments are greatly appreciated, Pasha.



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