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Forum: Geometry
Re: Question Should I worry about this warning? (Svetlana Shasharina)
Date: 11 Apr, 2016
From: John Apostolakis <John Apostolakis>

Dear Svetlana,

It is difficult to give a general recommendation about the warning you saw.

Sometimes it means the geometry is poorly defined - it includes non-trivial overlaps or possibly many small overlaps.  If this happens, typically you will see the warning relatively frequently.  

If so, it is better to check your geometry description for overlaps - please see the Geant4 User Guide for Application developers for recommendations how to do this.

If you see this rather infrequently, it is possible that it is due to a difficulty of the Navigator in Geant4 to understand whether a point is in one volume or a neighbour.  Likely this occurs because 
   - there are several solids along a line, or 
   - potentially due to inaccuracies in creating a volume - on one side of an interface the surface is described to a certain approximation and on the other side it is described with a different approximation or at least with a different set of points.  

This all depends on the complexity of the geometry which you have described, and the manner in which it was translated from STEP to STL.  If you can determine the number of triangles used to describe the solid “-Detector_two_stack_v203Geom_vol-” it could help inform. 

One thing that you can try, to help identify whether the Navigator is confused, and whether the solid(s)/volume(s) provide conflicting answers is to run with the Navigator in ‘check’ mode.  Please see the User Guide to find how to turn this on.

Best regards,
John
===================================================
John Apostolakis,  EP Department, CERN
SFT (SoFTware for Experiments) Group
Office: Building 32/ room R-003 (ground floor),  Mail: J27210
Email:  john.apostolakis@cern.ch       Office Tel:  +41-22-767-7239
------------------------------------------------------------------------------------------

> On 09 Apr 2016, at 15:03, Svetlana Shasharina <sveta@txcorp.com> wrote:
> 
> 
> *** Discussion title: Geometry
> 
> I am using geant4-10 patch 3.  Getting:
> ------- WWWW ------- G4Exception-START -------- WWWW -------
> *** G4Exception : GeomNav1002
>      issued by : G4Navigator::ComputeStep()
> Track stuck or not moving.
>          Track stuck, not moving for 10 steps
>          in volume -Detector_two_stack_v203Geom_vol- at point (-2.94654,0.122429,-8.43648)
>          direction: (-0.0160609,0.671728,-0.740624).
>          Potential geometry or navigation problem !
>          Trying pushing it of 1e-07 mm ...Potential overlap in geometry!
> 
> Geometry comes from STEP, translated to STL and then to GDML.
> 
> Should I worry? If not, is there a way to turn this off in the .mac
> file? Thanks, Sveta
> 
> -------------------------------------------------------------
> Visit this GEANT4 at hypernews.slac.stanford.edu message (to reply or unsubscribe) at: 
> http://hypernews.slac.stanford.edu/HyperNews/geant4/get/geometry/1461.html 

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1 None: Re: Should I worry about this warning?   (sveta - 11 Apr, 2016)
(_ None: Re: Should I worry about this warning?   (John Apostolakis - 11 Apr, 2016)
1 None: Re: Should I worry about this warning?   (sveta - 11 Apr, 2016)
2 None: Re: Should I worry about this warning?   (sveta - 11 Apr, 2016)
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