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Forum: Geometry
Re: Question Daughter volume sharing a surface with its mother (Andrea Conti)
Date: 07 Dec, 2014
From: Michael H. Kelsey <Michael H. Kelsey>

On Sun, 07 Dec 2014 23:24:35 GMT, Andrea Conti wrote:
> There have already been many questions about holes: in general, it is
> quite clear that the best way to implement a filled hole in a host
> material is to represent the hole as a daughter volume of the holed
> volume, with the filling material as material of the daughter (or air if
> the hole is hollow).
> 
> But this way the daughter will share a surface with the mother (that is,
> the mouth of the hole, on the same plane as the host material's surface)
> and nobody addressed this problem: is it acceptable ? Or are there going
> to be problems with the consistency of the geometry ?

If the surfaces are simple planes along X, Y or Z, then you can do this safely as the coordinate of the surface will be floating-point identical in the two cases. If the surface (even a plane) is not exactly on-axis, you are likely to have situations where the computation of the two surfaces do not coincide. In these cases, particles can get "trapped" between the surfaces, or you can have unexpected boundary interactions, etc. This is why we generally discourage shared surfaces, because the cases where they are safe are quite limited.

If your situation is a through hole, or a cavity in which the material is the same as the material surrounding the volume (e.g., a cube with a beam aperture through it), then you might be better off implementing it as a boolean (G4SubtractionVolume) or as a tesselated solid where you compute surface facets externally. In that case, when you place the volume in the mother, the hole will automatically be filled with the surrounding medium (air, vacuum, whatever).

  -- Michael Kelsey

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1 Ok: Re: Daughter volume sharing a surface with its mother   (Andrea Conti - 08 Dec, 2014)
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