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Forum: Geometry
Re: Question Geometry Parameterization (Matt Worden)
Date: 06 Nov, 2009
From: Gabriele Cosmo <Gabriele Cosmo>

> I have created a sphere and tried to put 121 cylinders next to the sphere.
> When I shoot a particle into the sphere, a the resultant photons will not
> travel into the cylinders. I checked for overlapping using the placement
> parameters and there is none.
> I just tried to make an array of union solids and add one cylinder to the
> sphere then add one cylinder to that union solid, and so on until I got all
> 121 cylinders on it.
>
> The code builds but there is a bus error mid run.

Both solutions attempted [(a) placements, and (b) union of tubs] are valid ones
and should work if the geometry and the optics setup are defined correctly.
BTW, if you post the complete code, we may be able to help with less words...
For (a), it should be verified that the tubes are indeed sharing the surface with
the cut-sphere, you can verify that by shooting geantinos perpendicular to the
shared surfaces and see what tracking says when crossing.
For (b), you must assure that tubes are instead intersecting the sphere (i.e. define
them slightly longer) in order to create a valid union.
Creating a BREP is a solution (BTW, examples for patching a BREP solid can be
found in the BREP library itself looking at the concrete solids, tub/box/polycone/...,
defined therein), but makes little sense here since would be rather inefficient.

Cheers, Gabriele

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