How to get the uv positions of vertices in a torch tensor effectively?

[aGIToz]

Hello all,
Big thanks for your endeavors in bringing machine learning to 3D world !

Here is my question :
I load an obj file.

verts, faces, aux = load_obj("obj.obj")

I can easily check

I can also see each face is composed by which nodes and which texture_ids :

Above here, one can see that the zeroth face (faces[0]) is constructed of the vertices [1,2,0] and texture_idx [0,1,2].

From the faces.texture_idx and aux.verts_uv I can find uv position of the each face

Like above here, I look for position of the zeroth face in the uv plane and aux.verts_idx[0], aux.verts_idx[1] and aux.vert_idx[2] gives me the position of the faces[0] in the uv plane (if I am wrong here then please correct me).

Also by looking at faces.verts_idx[0] and faces_texture_idx[0], I understand that vertex 1 corresponds to texture_idx 0 (and so vertices 2 and 0 to texture_idx 1 and 2 respectively ). Which means that uv position of the vertex 1 is given by aux.verts_uvs[0] i.e. tensor([0.9934, 0.4822]) and hence for the other two vertices 2 and 0, I can get their uv position (again, correct if I am wrong here).

My question is how to get the those uv positions of all the vertices [0, 1, 2, 3, ... 117] in a torch tensor? I can think of way in loops, but is there an effective way get the uv positions of the vertices?

[nikhilaravi]

@aGIToz so if I understand correctly you want to get the (V, 2) tensor of the uv coordinate for each vertex in the mesh? When using a uv representation of texture, you are not guaranteed to have the same uv coordinate for each vertex. That's why the indices of the faces.textures_idx into aux.verts_uvs can be different from the faces_verts_idx.

pytorch3d/pytorch3d/io/obj_io.py

Lines 168 to 173 in 95707fb

	- verts_uvs: FloatTensor of shape (T, 2), giving the uv coordinate per
	vertex. If a vertex is shared between two faces, it can have
	a different uv value for each instance. Therefore it is
	possible that the number of verts_uvs is greater than
	num verts i.e. T > V.
	vertex.

What is your use case for needing the uv coordinate per vertex?

[aGIToz]

The use case is; if I have uv position coordinates per vertex then I can get the textures associated with the vertices from the aux.texture_images (the texture map). This allows me to convert the obj mesh to point cloud with texture (color) per vertex.

I need it as I work on textured point cloud and often I am looking for a particular kind of texture to validate an algorithm, and often I find those textures in .obj files.

I do see your point that T > V , when a vertex is shared by multiple faces it may have different uv position coordinates, in that case one can go for average value of texture in texture map corresponding to each uv position.

[gkioxari]

Hi @aGIToz
If I understand correctly, this is not an issue with the library but you are seeking for help on how to get something done. While we appreciate you posting here, I think the Discussions forum in github is a better place for such questions than the issue page which is for bugs or feature requests for PyTorch3d.

If I am mistaken and this is a bug report, please provide a reproducible test case with a compact code snippet and data that will allow us to get to the error.

[aGIToz]

Hello,
Yup you are right this is exactly: How to do X with torch3d?

I was not aware of the Discussions tab, I apologize for positing it here. I will move it there.

But apparently when one creates a new issue from the Issues tab it also shows this option of How do i do X ..

[aGIToz]

Moved to discussion-588