Re: ROOT & GEANT

Pasha Murat (murat@cdfsga.fnal.gov)
Tue, 24 Feb 1998 16:50:15 -0600 (CST)


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.