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Question Re: For John Allison: how come I get "unknown faces!!" when hollowing out a box? 

Keywords: Boolean Processor error unknown faces G4SubtractionSolid
Forum: Geometry
Re: Sad For John Allison: how come I get "unknown faces!!" when hollowing out a box? (Blair Smith)
Re: None Re: For John Allison: how come I get "unknown faces!!" when hollowing out a box? (Blair Smith)
Date: 12 May, 2005
From: Blair Smith <bmsmith@lsu.edu>

John, just one quick question about this way of hollowing out solids.

Does using a parent-child pair in this way ever give funny results. e.g., if I was to ask for the mass of the mother (say filled with lead), would geant's G4VSolid class methods "know" to subtract the mass of the inner daughter volume (say filled with air or vaccum)?

I assume geant should correctly take into account the mass of all nested child volumes of a mother. Come to think of it I read some such documentation a while ago, but I can't recall where precisely. I guess I'd like to know how masses of parent volumes are calculated, do they include the mass of all children? If so, how do I request JUST the mass of the "virtual boolean" solid that I've just defined using the mother-daughter trick without recourse to G4SubtractionSolid? i.e., I want JUST the mass of my hollow housing, not the total mass that is enclosed by that volume! OK, OK, I can do it quicker by hand for a box or sphere I know, but what if, for arguments sake, I had a really ugly unioned volume with a hollow middle? Would I be forced to do it all by hand by calling the density of materials and volume methods for all the child volumes?

Oh, and why do you Europeans use the sexist "mother/daughter" jargon when "parent/child" is just as good and more pleasant? ;-)

I have a different question about how to compute bounding boxes for general solid regions, but I'll start another thread for that. -- Dr Blair M. Smith Medical Physics Program Department of Physics & Astronomy Louisiana State University Baton Rouge, LA

John Allison wrote:

>*** Discussion title: Geometry
>Email replies to PublicHyperNews@slac.stanford.edu must include:
>  In-Reply-To: <"/geometry/384/1/1"@geant4-hn.slac.stanford.edu>
>  Subject: ...change this to be about your reply.
>
>I think a hollow box is a problem because no surface of the subtractor
>intersects any surface of the subtractee. I think this case is just not
>anticipated because it is more efficiently handled by placing a daughter
>inside a mother volume -- the implicit convention (from the first
>beginnings of GEANT) are that the daughter replaces -- in effect
>subtracts from -- the mother space.
>
>I agree a more sensible error message should be issued.
>

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1 None: Re: For John Allison: how come I get "unknown faces!!" when hollowing out a box?   (John Allison - 13 May, 2005)
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