[Gate-users] RE : Brothers volumes at the same position what's occuring

[MELISSAS Maximilien (SAFRAN)]

Hi David and Simon,
Thanks for your answers,

The tree structure (and what I see) makes your second rules quite likely,
but I keep in mind that the behavior is not trustable, and I make sure to avoid crossing volumes when doing more tests (However the crossing volume approximation seems to be a good first-order description of a weaving). But I do have voxelised and segmented images of the geometry.  and switching to a voxelised geometry is on my short-term roadmap.

Cheers,
Maximilien

________________________________
De : Simon Stute [gate.stute at gmail.com]
Date d'envoi : jeudi 27 février 2014 17:17
À : David Sarrut
Cc : MELISSAS Maximilien (SAFRAN); gate-users at lists.opengatecollaboration.org
Objet : Re: [Gate-users] Brothers volumes at the same position what's occuring

Hi,

David is right, there should not be overlapping volumes, but still I think we can predict what happens ;-)

The first rule is that the particle will be in the first volume it crosses. If it continues its way in this volume while passing through an overlapping volume, it will ignore the overlapping volume until it exits the first volume (because G4 uses DistanceToIn and DistanceToOut strategies to compute the way in/out through the different volumes).

The second rule is (I don't know it but I deduce it from your experiment), if it crosses 2 (or more) volumes at a same place while being in another volume, it will enter the last declared volume, because volumes in G4 are organised as a tree, and I can imagine that when scanning the tree, the program always does it in the same way (so here probably by starting with the last volume).

Still, be careful with overlapping volumes !

Cheers,
Simon



On Thu, Feb 27, 2014 at 5:06 PM, David Sarrut <David.Sarrut at creatis.insa-lyon.fr<mailto:David.Sarrut at creatis.insa-lyon.fr>> wrote:
Hello,

In G4 (thus in gate), you could *not* have overlapping volumes. If some volumes overlap, the result is undefined. To my knowledge, you don't have the choice, you need to change your geometry.

There is a feature in G4 to deal with overlapping volumes (called parallel world), but it is not available through gate.

Sincerely,
David

Le jeudi 27 février 2014, MELISSAS Maximilien (SAFRAN) <maximilien.melissas-alten at safran.fr<mailto:maximilien.melissas-alten at safran.fr>> a écrit :

Dear Gaters,

A question related to my question from yesterday,
When 2 brothers volume are crossing, what's happening at the crossing point.
Here is a quick example of what I mean, with a mother box having 2 daughters volume Castor and Pollux
/gate/motherbox/daughters/name Castor
/gate/motherbox/daughters/insert cylinder
/gate/Castor/geometry/setHeight 20. mm
/gate/Castor/geometry/setRmin 0. mm
/gate/Castor/geometry/setRmax 5. mm
/gate/Castor/placement/setTranslation +2. -0. 0.  mm

/gate/motherbox/daughters/name Pollux
/gate/motherbox/daughters/insert cylinder
/gate/Pollux/geometry/setHeight 20. mm
/gate/Pollux/geometry/setRmin 0. mm
/gate/Pollux/geometry/setRmax 5. mm
/gate/Pollux/placement/setTranslation -2. -0. 0.  mm

these  volumes should have a big overlap at the center of motherbox.

Now what's occuring when a particle pass through the middle of motherbox ?
Is the particle inside of Pollux ?
Is the particle inside of Pollux and Castor, and can interact with both
Does the particle belong to the first volume it crossed ?


If the last the volume always on-top ?  If yes, this answers my question from yesterday,
the later-declared volume being on-top photons spend more time inside this one and thus scatter more from the last one.

Cheers,
Maximilien

________________________________



Maximilien MELISSAS

Consultant, Alten technology

Image processing for CT NDT @ Safran composite

http://www.alten.com
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