obj file loaded as Scene object instead of Trimesh object

Hi,

I’m trying to load a mesh from an .obj file (from ShapeNet dataset) using Trimesh, and then use the repair. fix_winding(mesh) function.

But when I load the mesh, via trimesh.load('/path/to/file.obj') or trimesh.load_mesh('/path/to/file.obj'), the object class returned is Scene, which is incompatible with repair. fix_winding(mesh), only Trimesh object are accepted.

How can I force it to load and return a Trimesh object or parse the Scene object to Trimesh object?

[jackd]

My understanding is that some .obj files specify different sub-meshes. trimesh attempts to recreate this as faithfully as possible. You can always concatenate the meshes together, though not all aspect have concatenation which is supported. If all you care about is the vertices/faces, you can use something like the following:

import trimesh


def as_mesh(scene_or_mesh):
    """
    Convert a possible scene to a mesh.

    If conversion occurs, the returned mesh has only vertex and face data.
    """
    if isinstance(scene_or_mesh, trimesh.Scene):
        if len(scene_or_mesh.geometry) == 0:
            mesh = None  # empty scene
        else:
            # we lose texture information here
            mesh = trimesh.util.concatenate(
                tuple(trimesh.Trimesh(vertices=g.vertices, faces=g.faces)
                    for g in scene_or_mesh.geometry.values()))
    else:
        assert(isinstance(mesh, trimesh.Trimesh))
        mesh = scene_or_mesh
    return mesh

[mikedh]

Yeah the material concatenation is pretty expensive, we could add Yet Another Keyword Argument™️ to the OBJ loader haha. It still complains about concatenation because it’s still loading UV coordinates, but speeds it up by an order of magnitude:

In [7]: %timeit m = trimesh.load('bigmodel/bigben/model.obj', force='mesh', skip_texture=True)
concatenating texture: may result in visual artifacts

123 ms ± 1.16 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)

In [8]: %timeit m = trimesh.load('bigmodel/bigben/model.obj', force='mesh', skip_texture=False)
concatenating texture: may result in visual artifacts

1.9 s ± 27.4 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)

Happy to include in the next release if that’s useful.