Pyvista: Segmentation fault while visualizing Trimesh object

[KeunwooPark]

Describe the bug, what's wrong, and what you expect:
Hi. I'm trying to visualize a Trimesh object.
However, when I create PolyData with vertices and faces from a Trimesh object, PyVista crashes with Segmentation fault.

Current thread 0x00007f37a53f5740 (most recent call first):
  File "/(erased)/lib/python3.6/site-packages/pyvista/plotting/renderer.py", line 1267 in reset_camera
  File "/(erased)/lib/python3.6/site-packages/pyvista/plotting/renderer.py", line 377 in add_actor
  File "/(erased)/lib/python3.6/site-packages/pyvista/plotting/plotting.py", line 465 in add_actor
  File "/(erased)/lib/python3.6/site-packages/pyvista/plotting/plotting.py", line 1507 in add_mesh
  File "/(erased)/lib/python3.6/site-packages/pyvista/plotting/helpers.py", line 111 in plot
  File "viz_test.py", line 12 in <module>
Segmentation fault (core dumped)

I could not find an example of Trimesh objects. What am I doing wrong?

To Reproduce
This is the .ply file that I'm using.
tmp.zip

This is the code. The file works fine when I directly use PyVista.

import trimesh
import pyvista as pv
import numpy as np

file_name = 'tmp.ply'
tmesh = trimesh.load(file_name)
print(tmesh.vertices)
print(tmesh.faces)

# not working
pmesh = pv.PolyData(np.array(tmesh.vertices), np.array(tmesh.faces))
pmesh.plot()

# working
mesh = pv.read(file_name)
mesh.plot()

Screenshots
This is how the mesh looks like.

---

System Information:

--------------------------------------------------------------------------------
  Date: Wed Oct 28 14:58:00 2020 KST

                OS : Linux
            CPU(s) : 8
           Machine : x86_64
      Architecture : 64bit
       Environment : Python
        GPU Vendor : NVIDIA Corporation
      GPU Renderer : GeForce GTX 1060 6GB/PCIe/SSE2
       GPU Version : 4.5.0 NVIDIA 455.23.05

  Python 3.6.9 (default, Oct  8 2020, 12:12:24)  [GCC 8.4.0]

           pyvista : 0.26.1
               vtk : 9.0.1
             numpy : 1.19.2
           imageio : 2.9.0
           appdirs : 1.4.4
            scooby : 0.5.6
            meshio : 4.3.2
        matplotlib : 3.3.2
             scipy : 1.5.3
--------------------------------------------------------------------------------

[github-actions[bot]]

Hi and welcome! Thanks for posting your first issue in the PyVista project! Someone from @pyvista/developers will chime in before too long. If your question is support related, it may be automatically transferred to https://github.com/pyvista/pyvista-support

[darikg]

I think there's just a mismatch between tmesh's and vtk's face representations. In vtk the faces need to specify the number of vertices per face, so

n_face = tmesh.faces.shape[0]
faces = np.concatenate([3 * np.ones((n_face, 1), dtype='int'), tmesh.faces], axis=1)

Kind of a minorly user-unfriendly footgun though for sure

[KeunwooPark]

Thank you very much! This works well.
It would be better if PyVista shows an interpretable error. Maybe throwing an error before the segmentation fault.

[akaszynski]

I'm actually adding a new feature that allows you to wrap a trimesh object. See #970. This should clean up any issues.

The only way we could protect the user from a segfault is checking the consistency of the mesh prior to sending it out to VTK, and to walk through the mesh we'd have to implement something in C/cython, which we might do down the road at some point. For now, I think wrapping the mesh ensures that you get a valid mesh and we can consider adding consistency/validity checking down the line.