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Forum: Geometry
Re: Question Hole in a conical section (Estela Suarez)
Re: None Re: Hole in a conical section (John Allison)
Date: 25 Nov, 2009
From: John Apostolakis <John Apostolakis>

In case you need(ed) additional information, I had some additional  
suggestions and comments:

On Nov 24, 2009, John Allison wrote:

> To see graphics that relies only on tracking, use RayTracer(X).

I strongly urge you to use this visualisation option, to double check  
your geometry.   It uses the exact geometry description you have  
created to track the rays.  Due to this it can diagnose issues in a  
geometry which cannot be seen otherwise.

(The visualisation simplifies the geometry in all cases, and has a  
difficult task in the case of boolean solids.)

On Nov 23, 2009, Estela Suarez wrote:

> When I put my detector in the hole and fire it with many particles I  
> don't get any segmentation violation, which I
> think would be the case if I would have volumes superimposed.

Only occasionally will an overlap cause a segmentation fault.   
Typically the behaviour is just not well define - e.g. locating the  
volume for a position which is in an overlap region can depend on the  
state of the navigator before that call.

For boolean solids (and other challenging shapes) the best ways to  
ensure that the geometry is well described, and that overlaps are not  
occurring are:
   - to use the newest overlap detection method (add a parameter at  
the end of the G4PVPlacement constructor to check whether a volume  
overlaps when you define it - see the documentation for details);
   - visualise it using the RayTracer (as above);
   - set the Check Mode when tracking (both for the RayTracer and for  
particles in your simulation) by using the commands
     /geometry/navigator/check_mode true
     This will do extra checks during the navigation, and report any  
problems which it finds.  It is not guaranteed to find any and all  
problems, but does try to report all the potential issues it finds and  
the additional checking should not be a large overhead.

      For more information, in case you find a likely problem you can  
use an additional flag during the debugging of your geometry that will  
give additional information as it does this checking:
          /geometry/navigator/verbose           1

     I hope that these suggestions can enable you to verify your  
geometry.

     Best regards,  John Apostolakis

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1 Question: Re: Hole in a conical section   (Estela Suarez - 25 Nov, 2009)
2 Question: Re: Hole in a conical section   (Estela Suarez - 25 Nov, 2009)
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