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Forum: Geometry
Re: Question Overlap with mother volume ! (Ioan-Charly)
Date: 05 Aug, 2014
From: John Apostolakis <John Apostolakis>

Dear Ioan-Charly

I am pleased to see that you have run the geometry checking functions, in order to verify your setup.  It is an important check, and I would recommend it both for consistency checking (preventative) and for diagnosing what appear to be unexpected physics results.

It is very possible that unexpected physics results are due to a geometry error of this type.

Please find below some feedback and suggestions for fixing the problem underlying these error messages.

John
===================================================
John Apostolakis,  PH Department, CERN

On Aug 5, 2014, at 1:00 AM, Ioan-Charly <itkint@ulb.ac.be> wrote:

> 
> *** Discussion title: Geometry
> 
> Hi,
> 
> For me i have a simple geometry three tubs of 10mm radius and 5um thick
> for the first one, 400um for the second one and for the last one 5cm.
> 
> When i run the command /geometry/test/run, i have this message :
> 
> Running geometry overlaps check...
> Checking overlaps for volume Wtarget ... 
> -------- WWWW ------- G4Exception-START -------- WWWW -------
> *** G4Exception : GeomVol1002
>      issued by : G4PVPlacement::CheckOverlaps()
> Overlap with mother volume !
>          Overlap is detected for volume Wtarget
>          with its mother volume world
>          at mother local point (4.95596,-6.80934,-0.505002), overlapping by at least: 6.80934 mm 
> NOTE: Reached maximum fixed number -1- of overlaps reports for this volume !
> *** This is just a warning message. ***
> -------- WWWW -------- G4Exception-END --------- WWWW -------

Please check where you have placed the volume Wtarget.

It is protruding by 6.8 mm outside its parent (mother) volume.

The point where it is protruding is at location (4.95596,-6.80934,-0.505002) in the coordinate system of the mother volume.

Once you have understood why this happens ( is it due to an incorrect location or rotation, or is it simply a larger volume than you meant to create ), you can adjust the relevant parameter.

The remaining problems are similar.  The key words are 
   'Overlap with mother volume ! '
which explain the type of overlap found.

Good luck in identifying the issue, and correcting it.


> Checking overlaps for volume Windtarget ... 
> -------- WWWW ------- G4Exception-START -------- WWWW -------
> 
> I am interested of the geometry management because i had some strange
> result... Indeed, when i gun some electron of 0.1MeV the azimuthal
> distribution are not uniform. However, it must be!
> 
> How can i fix this overlap and


> [Is it] possible that the "strange" result is caused by the overlap ?

Yes, physics results are altered by errors in the geometry of this type.

Regards,
John 

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> Visit this GEANT4 at hypernews.slac.stanford.edu message (to reply or unsubscribe) at: 
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1 None: Re: Overlap with mother volume !   (Ioan-Charly - 05 Aug, 2014)
(_ None: Re: Overlap with mother volume !   (Michael H. Kelsey - 06 Aug, 2014)
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