In the SceneParameters, how to know one's parent?

[Mephisto405]

For instance, when we load a scene file, we can see a table of SceneParameters with columns Name, Flags, Type, and Parent as below.
What I want to do is to get the parent of an instance.
That is, I want to make sure the parent of the params['Floor.to_world'] is Rectangle.
Ultimately, I want to obtain the world transformation of shapes whose parents are Rectangle to get the coordinates of the four corner points of all rectangles.

scene = mi.load_file("data/cornell-box/scene_v3.xml")
params = mi.traverse(scene)
print(params)

[njroussel]

Hi @Mephisto405

I don't believe there's a built-in mechanism to do this. You can either parse the output of mi.traverse() to detect parameters which have the Parent you are searching for, or you can rename your scene objects in your scene description to include this information and then use SceneParameters.keep(some_regex_that_matches_your_parent_type)

[ziyi-zhang]

I want to obtain the world transformation of shapes whose parents are Rectangle to get the coordinates of the four corner points of all rectangles

If it's for visualization purpose, I have the following workaround

# iterate over all shapes
obj = scene.shapes()[idx]
params = mi.traverse(obj)
if obj.__repr__().startswith('Rectangle'):
        v = np.array([[-1.0, -1, 0], [1, -1, 0], [1, 1, 0], [-1, 1, 0]])
        f = np.array([[0, 1, 2], [0, 2, 3]])
        v_ = params["to_world"] @ mi.Point3f(v)
        v = v_.numpy()

[Mephisto405]

@njroussel @ziyi-zhang
Yo, early bird bros!!! So thankful for your fast reply and helps XD.
I now feel safe that many guys would help me if I do something wrong with Mitsuba 3. kkk
Very thankful again!

I just found another mechanism to achieve this, so I am sharing it here:

# it use `properties` dictionary of `SceneParameters` object
params.properties['Floor.to_world'][2].__repr__().startswith('Rectangle')