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

[maxime]

Dear Howard,

I opened your STL with Blender (https://www.blender.org <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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.opengatecollaboration.org/pipermail/gate-users/attachments/20200707/3ca3f74c/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Screenshot 2020-07-07 at 11.32.04.png
Type: image/png
Size: 390281 bytes
Desc: not available
URL: <http://lists.opengatecollaboration.org/pipermail/gate-users/attachments/20200707/3ca3f74c/attachment-0001.png>