indoor scenes cannot be previewed properly, and errors seem to be reported when materials are set to transparent

[summer2ice]

Have you ever encountered a situation where you can't preview the interior scene? In addition, when the mouse is dragged into the room, the object shows red and cannot be identified, in this case, how should I solve @it?

[steffenitely]

Hi @yibingXia ,

i had a similar issue - take a look at #532 . The problem is that the render/preview can't handle transparent properties so in order to create invisible objects the BSDF needs to be changed manually into a null BSDF inside the exported .xml file.

Hope this quick answer helps!

[steffenitely]

Hi @summer2ice

If I understand the code screenshots correctly, it seems that the null BSDF might not have been declared properly. The structure should look like this:
<bsdf type="null" id="mat-itu_concrete" name="mat-itu_concrete"> </bsdf>

It is important that the bsdf type is set tu null. Note that this will make the objects using the material completley invisible. Partial transparency is to my knowledge not supported.

Hope this helps!

[summer2ice]

Hi @steffenitely : Good morning, thank you for your reply, it doesn't seem to work. If it is changed to null, the import scene displays an error:

This is effective by setting the appropriate clip at value. When I was calculating the path, the error message was displayed：
ValueError: Material 'itu_concrete.002' is used by the object 'Plane_001' but not defined.
I checked the meshes folder, there is Plane_001, I do not know where is the problem

[steffenitely]

When copying objects in blender it creates a copy of the material as well. That's why you have itu_concrete.001 and .002 and so on. Since only itu_concrete and not itu_concrete.002 is predefined you can either change the materials inside blender so they all use the material itu_concrete or you create custom materials in sionna for each material used in your scene.

[merlinND]

@summer2ice the error that you showed ("unreferenced object Principled BSDF (...) within bsdf of type null") suggests that you did something like this in the XML file:

<bsdf type="null" id="mat-itu_concrete" name="mat-itu_concrete">
    <bsdf type="principled">
        ....
    </bsdf>
</bsdf>

whereas as @steffenitely suggested, you should only have the null BSDF, nothing inside:

<bsdf type="null" id="mat-itu_concrete" name="mat-itu_concrete"> </bsdf>

[summer2ice]

@merlinND Thank you for your reminder, it is work

[merlinND]

Hello @yibingXia,

To help preview scenes that are enclosed, we introduced the clip_at argument of the preview function: https://nvlabs.github.io/sionna/api/rt.html#sionna.rt.Scene.preview

Regarding pink objects, I believe it means that they are using a BSDF (material) in Blender that is not supported in Mitsuba. The mitsuba-blender exporter exports them as pink so that it's easy to see that an unsupported BSDF was used.
You can try assigning a supported material, such as Diffuse to these objects and try exporting again.

[summer2ice]

@merlinND Good morning. Thanks for your advice, this is effective by setting the appropriate clip at value.
These objects are already allocated and the material is already diffuse, but they still show pink objects, there's still some confusion for me

[merlinND]

These objects are already allocated and the material is already diffuse, but they still show pink objects,

I believe that the material used in Blender is not "diffuse" or a supported Mitsuba material, so the exporter replaces it with this pink diffuse material when exporting the scene to Mitsuba XML.
If you go back to your scene in Blender and check the material (shader), you should be able to change it to Diffuse and set the color of your choice. Then, when re-exporting the scene, the objects will no longer be pink.

[summer2ice]

@merlinND Thank you, it is effective as you suggested. At the same time, I have another question, if it is changed to "diffuse reflection", whether it means that the surface of such materials will not have specular reflection or diffraction, because when I calculate the path, I will prompt an error: ValueError : Material 'itu_concrete.002' is used by the object 'Plane_001' but not defined.
I'm trying @steffenitely suggested , but I still can't solve and understand, so I can't verify this phenomenon right now.
Thank you in advance for your answers~

[merlinND]

Hello @summer2ice,

if it is changed to "diffuse reflection", whether it means that the surface of such materials will not have specular reflection or diffraction

That's a fair question. It can be a little confusing, but the materials set in Blender and that you can see in the XML file ("diffuse", "principled", etc) are only used for visual rendering, when calling e.g. scene.render().

For radio simulation, what matters are the radio materials, which are:

1. Set automatically based on the name of the material, e.g. name="itu_concrete" will have an ITU concrete radio material,
2. Can also be overridden / tweaked from Python.

---

That being said, the error message that you see:

ValueError : Material 'itu_concrete.002' is used by the object 'Plane_001' but not defined.

is likely due to the fact that when you inserted a null material, you did not give it the right name. For example, if you replaced:

<bsdf type="null" id="itu_concrete.002" name="itu_concrete.002">
    <bsdf type="principled">
        ....
    </bsdf>
</bsdf>

with:

<bsdf type="null" id="some-other-name" name="some-other-name"> </bsdf>

then the material itu_concrete.002 is no longer defined. Just add that name back to the null material you inserted:

<bsdf type="null" id="itu_concrete.002" name="itu_concrete.002"> </bsdf>