# RE: BOX & axes

From: Chris Theis (Christian.Theis@cern.ch)
Date: Thu Jan 25 2007 - 17:55:21 CET

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Hi Florian,

Thanks for the quick answer, but as discussed the issue is a little more
subtle than it seems at first glance. I'll try elaborate on it in more
detail to explain the actual question:

Usually, you define a box with a point (let's call it v) and three
vectors h1, h2, h3 which all have a certain length. The nice thing about
this is that you can implicitly define an arbitrary rotation. However,
this is also where things become more tricky. For example if one wants
to determine rotational angles from the basis formed by the h vectors it
matters whether they form a left or a right-handed coordinate system.

Thus, I was wondering whether FLUKA imposes any requirement on the
specification of the h vectors (e.g. h1 crossprod h2 = h3)? I currently
have an old input where I found a box with a left-handed coordinate
system formed by the h vectors and I was not sure what FLUKA does in
that case and if that poses a problem which is probably not obvious at
the first look, like for example an RPP where min & max is accidentally
swapped.

Cheers
Chris

> Dear Chris!
>
> I think there is a misunderstanding. As far as I know the 3
> vectors do not define height, width and length. Each of these
> vectors lie on one edge of the box and the length of each
> vector is the length of the edge.
> If you look into the manual p255 fig 8.2 (CERN, yellow
> report) you find a drawing how it works.
>
> Hope this helps.
>
> Regards, Florian
>
>
>
> Chris Theis wrote:
> > Hello,
> >
> > I'm currently dealing with an old input file which uses BOX
> > definitions and came across the following issue, which is
> not really clear to me.
> > According to the manual the user has to define an origin of
> the box +
> > 3 vectors for height, width & length. Furthermore, it's a
> requirement
> > that the user ensures perpendicularity of those vectors. However,
> > nothing is stated with respect to the orientation of the basis
> > generated by those vectors. I'm not sure whether it is a
> requirement
> > that they form a right-handed coordinate system and what is
> the effect
> > if a left-handed system is (accidentally) supplied?
> Probably somebody
> > could shed some light on this issue.
> >
> > Thanks in advance
> > Chris
> >
> >
>
>
> --
> ###########################################
> Florian Sommerer
> European Organization for Nuclear Research CERN DSU/TT
> Mailbox Z08700 Geneve 23
> CH-1211 Switzerland
> Tel : +41 2276 75582
> ###########################################
>

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