Problem 260

Summary: strange behaviour in optimization time when closing geometry
Product: Geant4 Reporter: V.Hejny
Component: geometry/solidsAssignee: Gabriele Cosmo <Gabriele.Cosmo>
Status: RESOLVED FIXED    
Severity: normal CC: Vladimir.Grichine
Priority: P2    
Version: 3.1   
Hardware: PC   
OS: Linux   
URL: http://ikp427.ikp.kfa-juelich.de/G4testSTT.tar.gz

Description V.Hejny 2001-06-01 02:49:12 CEST 
We are simulating a set of straw tubes (i.e. some small gas tubes arranged
on a tube surface around the beamline) where the layers are rotated with a
small angle (5-9 deg) versus each other.

If we put the tubes directly in the world volume, everything works fine.
If we use an additional (tube) mother volume (which, I think, should be the
normal strategy in a compound detector) the optimization after the first
/run/beamOn takes a lot of time and memory (>>100 MB). This does not rely
on the shape of the mother volume.

If we have no additional rotation of the tubes (i.e. all are parallel to the
beam axis) the problem is gone.

Is this a wanted behaviour of G4?

A test program showing the behaviour can be found at the given URL.
Comment 1 Gabriele Cosmo 2001-06-12 10:03:59 CEST 
This looks due to the current provisional strategy adopted in
G4Tubs::CalculateExtent().
Comment 2 Vladimir.Grichine 2001-11-21 02:28:59 CET 
The behaviour is reproduced for G4Box geometry and is sensitive to the ratio
of the mother/world dimensions. It should be considered by voxel optimisation
experts.
Comment 3 Gabriele Cosmo 2001-12-17 03:44:59 CET 
After investigation of the test case provided, it turns out that
the observed behavior is due to the complexity of the geometry to
determine the region to be voxelised. In this case, a rather 'dense'
region of volumes is placed in a large world. The class G4LogicalVolume
provides two functions GetSmartless()/SetSmartless(double) to help
address such cases and tune a smartless parameter for voxelisation for
specific volumes, in order to optimise the voxelisation process.
For future improvements in the area of geometry optimisation we're
planning to extend voxelisation in 3D space and automatically apply
smartless to critical areas (like in this case).
Thanks for the report.