From: Alfredo Ferrari (alfredo.ferrari@cern.ch)
Date: Mon Feb 11 2008 - 11:22:26 CET
Hi
in principle one can call the following subroutine:
CALL GEOREG ( X, Y, Z, NREG, IDISC )
where X, Y, Z are the coordinates of the point where you want to know the
region (returned in NREG) and the lattice (returned in MLATTC in common
LTCLCM). IDISC is a flag which if different from zero signals you are
already out or going out of the geometry.
Actually the situation is slightly more complex:
a) GEOREG is very CPU ineffective like all "point" like geometry calls: it
is ok to use it provided this is not done too often (geometry tracking
based on a sequence of GEOREG calls instead of real tracking calls
could be thousands of times slower in complex geometries). GEOREG
loops on all regions/lattices until it finds where the point lies.
On the contrary real step like calls can exploit many effective
optimizations which makes them able to check at maximum 2/3 regions
even in complex geometries
b) GEOREG should be called with care when X,Y,Z lies on the boundary
between two regions. This is a very common situation at run time, since
all steps meeting a boundary end up exactly in that situation.
The region returned by GEOREG in that case can be (pseudo-randomly)
any of the two regions separated by that boundary, and there is no
guarantee that the one returned is coherent with the one returned by
the last tracking step. More specifically, the last step direction
cosines are used to decide which region/lattice is returned (the one
returned is the one the direction is pointing "into" if X,Y,Z lies
on a boundary, even though the "current" direction referred to a
step in a completely different position). In case one wants to input
his own choice of cosines for this purpose (and for this purpose only),
the call to GEOREG must be preceded by a call to:
CALL GEOCRS ( TXX, TYY, TZZ )
where TXX, TYY, TZZ are the direction cosines (properly normalized to
1 in double precision)
c) It is safer to save MLATTC/NEWLAT (common LTCLCM) before the call to
GEOREG and restore them after, if GEOREG is called from unexpected
situations (ie in the middle of an event). Furthermore in those cases
the tracking optimization will be destroyed for the next step resulting
in some CPU penalty
It would be better to know more about where/why you need this info, in
order to help better in devising the correct solution.
Ciao
Alfredo
On Fri, 8 Feb 2008, Biagio Di Micco wrote:
> Dear all,
>
> I need a function that takes the coordinates of a point in input
> and returns the region number where the point is (and the lattice number, if
> it is a lattice replica).
> Is there any function in the FLUKA library that I can use?
>
> Thanks in advance
>
> Biagio
>
>
>
-- +----------------------------------------------------------------------+ | Alfredo Ferrari || Tel.: +41.22.76.76119 | | CERN-AB || Fax.: +41.22.76.69474 | | 1211 Geneva 23 || e-mail: Alfredo.Ferrari@cern.ch | | Switzerland || | +----------------------------------------------------------------------+
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