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Forum: Geometry
Re: Question G4VSolid::DistanceToOut(p,v,...) for p on surface? (Rickard Holmberg)
Re: Feedback Re: G4VSolid::DistanceToOut(p,v,...) for p on surface? (Vladimir Grichine)
Date: 06 Mar, 2007
From: Rickard Holmberg <Rickard Holmberg>

Vladimir.Grichine@cern.ch wrote:
> *** Discussion title: Geometry
> Email replies to PublicHyperNews@slac.stanford.edu must include:
>   In-Reply-To: <"/geometry/696/1"@geant4-hn.slac.stanford.edu>
>   Subject: ...change this to be about your reply.
>
> Hi Rickard,
>
>   
>> When trying to debug the G4TessellatedSolid problems I reported in
>> another thread here, I have run up against some other problems,
>> concerning DistanceToOut(p,v,...) when p lies on a surface.
>> The User's Guide for Toolkit developers states that DistanceToOut(p,v,...)
>> should behave as follows:
>> Return distance along the normalised vector v to the shape, from a point
>> at an offset p inside or on the surface of the shape. Intersections with
>> surfaces, when the point is not greater than kCarTolerance/2 from a
>> surface, must be ignored.
>>
>> I interpret that so that if we are close to a surface like that, the
>> function should return the distance to the next outgoing intersection,
>> if there is one.
>>     
>
> What is written in the user documents is correct.
> When the distance from surface is not greater than kCarTolerance/2 means
> that you are on the surface, therefore DistanceToOut(p,v,...) must return
> zero.
>   
Aha, so what the documentation is saying is that if the point is close 
to ANY surface, then intersections with ALL surfaces should be ignored? 
I interpreted it as if only the intersections with the nearby surface 
should be ignored. The ANY/ALL interpretation makes much more sense when 
comparing with code. I guess the plural on the surfaces in the 
documentation actually carries meaning...

Thanks for clearing that out, and sorry for making the sloppy 
interpretation.

    / Rickard Holmberg

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