[Gate-users] why an mesh object is not a solid volume

[Howard]

Hi Maxime,

Thanks for your reminder. I thought I replied to the mailing list as well.
I am forwarding our email exchange to the list now. Thanks for your help.

Best regards,
Howard

=======================================================

Hi Howard,

I’m glad that it works !

Please answer to the email list so everyone knows the solution. It is also
helpful for people facing the same issue in the future.

Best regards,
  Maxime Chauvin

On 8 Jul 2020, at 00:47, Howard <lomahu at gmail.com> wrote:

Hi Maxime,

You are absolutely right that the wrong normals are the culprit. After that
is fixed the mesh surface becomes a solid object indeed. Thank you very
much.

Howard

On Tue, Jul 7, 2020 at 5:41 AM maxime <maxime.chauvin at inserm.fr> wrote:

> Dear Howard,
>
> I opened your STL with Blender (https://www.blender.org) and I can see
> one problem with your STL:
>
>    - the normals are not all facing outwards, see attached screenshot.
>
>
> This means that GATE (Geant4) will not be able to create a closed volume
> from the STL,
> and therefore this ‘phantom’ will be transparent to X-rays.
>
> One easy solution is to ask Blender to recalculate the normals outside
> (Menu Mesh -> Normals -> Recalculate Outside) and then save (File -> export
> to STL, beware of the coordinates).
>
> The best is to revise the way you produce your STL so it is correct from
> the start. And then Blender is just an easy way to check the STL files you
> create.
>
> I believe it will now work in GATE.
>
> Good luck,
>   Maxime Chauvin
>
> <Screenshot 2020-07-07 at 11.32.04.png>
>


On Tue, Jul 7, 2020 at 5:41 AM maxime <maxime.chauvin at inserm.fr> wrote:

> Dear Howard,
>
> I opened your STL with Blender (https://www.blender.org) and I can see
> one problem with your STL:
>
>    - the normals are not all facing outwards, see attached screenshot.
>
>
> This means that GATE (Geant4) will not be able to create a closed volume
> from the STL,
> and therefore this ‘phantom’ will be transparent to X-rays.
>
> One easy solution is to ask Blender to recalculate the normals outside
> (Menu Mesh -> Normals -> Recalculate Outside) and then save (File -> export
> to STL, beware of the coordinates).
>
> The best is to revise the way you produce your STL so it is correct from
> the start. And then Blender is just an easy way to check the STL files you
> create.
>
> I believe it will now work in GATE.
>
> Good luck,
>   Maxime Chauvin
>
>
>
> On 7 Jul 2020, at 05:35, Howard <lomahu at gmail.com> wrote:
>
> Dear Gate-users,
>
> Is there anyone out there an expert on the tessellated volume? I generated
> a tessellated mesh object based on a 3x3 binary matrix:
>
> 0 1 0
> 1 1 1
> 0 1 0
>
> where 0 means completely opaque and 1 completely transparent. For some
> reason when I applied this volume in GATE as a phantom (set materials as
> Tungsten) for X-ray, there was no beam attenuation. In other words, this
> volume behaved like an empty shell instead of a solid piece. The STL file
> for this volume in ASCII format is attached to this email for your
> reference.
>
> It would be truly appreciated if any expert on tessellated volume can help
> out or suggest any software allowing us to look for more detail of the
> volume?
>
> Howard
> <ASCIITest3x3.stl>_______________________________________________
> Gate-users mailing list
> Gate-users at lists.opengatecollaboration.org
> http://lists.opengatecollaboration.org/mailman/listinfo/gate-users
>
>
>
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