o3d.io.read_triangle_mesh

[hernot]

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Describe the bug
A clear and concise description of what the bug is.

After loading *.obj file which has just one texture image 0_0.png

object_path = 3.obj
mesh = o3d.io.read_triangle_mesh(mesh_path)

a call to mesh.has_textures() returns False. Calling len(mesh.textures) returns a length of 2. Checking the two images it appears that the first image is an empty image where mesh.textures[0].is_empty() returns True whereas the mesh.textures[1] stores the actual texture image.

To Reproduce
see above

Expected behavior
The call to mesh.has_textures() should return true and len(mesh.textures) should return 1 and mesh.textures[0].is_empty() should return False.

The following can be used as workarround for now:

print(mesh.has_textures()) # -> False
if len(mesh.textures) > 1:
  mesh.textures = [ img for img in mesh.textures if not img.is_empty()]
print(mesh.has_textures()) # -> True if has one or more valid texture images otherwise False

**Screenshots**
not applicable 

**Environment (please complete the following information):**

- Operating system: Mint 19 (e.g. Ubuntu 19.04)
- Python version: Python 3.6
- Open3D version: 0.13. and latest development from above
- Is this remote workstation?: no
- How did you install Open3D?: pip 
- Compiler version (if built from source): wheel

**Additional context**

[ssheorey]

@hernot can you share the obj file with the read error? Are you able to read it correctly in another software?

[hernot]

I can. First i want to check some issues in preparing the Triangle mesh before writing if they could be the cause.

[hernot]

Sorry for the delay attached below a tar.gz archive containing two recordings
0.obj was created with open3D 0.13.0
1.obj was created with ooen3D 0.11.2

When loading 1.obj in open 3D version 0.13.0 i do see the spurious extra empty 0 texture image and all triangle materials are recoded to material 1
When correcting back to material 0 and removing empty 0 texture image so that texture is again displayed by
o3d.visualization.O3DVisualizer and saving afterwards to a new file texture is recoded again to 1 and in addition to empty 0 image also an additional empty texture 2 is added.
Have not explicitly checked if the same happens with 0.obj created after update to open3D 0.13.0.

I also tried to explicitly set the material id array but nothing changed.

StrangeEmptyTextures.tar.gz

Note:

Both surfaces have been created using python

[TiMMaTTiee]

Same problem here, reverted to 0.10.0 for now obj.zip

[ssheorey]

This works correctly in the latest Open3D (and likely in v0.16 as well):

$ open3d draw path_to_model.obj