Add IO for NPZ files for Tensor-based TriangleMeshes

[errissa]

The following script tests the basic functionality:

import open3d as o3d

# Load OBJ file
d = o3d.data.MonkeyModel()
mesh = o3d.t.io.read_triangle_mesh(d.path)
print(mesh)
o3d.visualization.draw(mesh)

# Save mesh as NPZ and reload it
o3d.t.io.write_triangle_mesh('monkey.npz', mesh)
mesh_npz = o3d.t.io.read_triangle_mesh('monkey.npz')
print(mesh_npz)

# Verify it looks correct
o3d.visualization.draw(mesh_npz)

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This change is 

[update-docs]

Thanks for submitting this pull request! The maintainers of this repository would appreciate if you could update the CHANGELOG.md based on your changes.

[errissa]

Texture maps are now supported. Try this updated script:

import open3d as o3d

# Load OBJ file
d = o3d.data.MonkeyModel()
mesh = o3d.t.io.read_triangle_mesh(d.path)
mesh.material.set_default_properties()
mesh.material.texture_maps['albedo'] = o3d.t.io.read_image(d.path_map['albedo'])

print(mesh)
o3d.visualization.draw(mesh)

# Save mesh as NPZ and reload it
o3d.t.io.write_triangle_mesh('monkey.npz', mesh)
mesh_npz = o3d.t.io.read_triangle_mesh('monkey.npz')
print(mesh_npz)

# Verify it looks correct
o3d.visualization.draw(mesh_npz)

[benjaminum]

Reviewable status: 0 of 2 files reviewed, 1 unresolved discussion (waiting on @errissa)

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cpp/open3d/t/io/TriangleMeshIO.cpp line 243 at r2 (raw file):

    }
    if (mesh.HasTriangleAttr("texture_uvs")) {
        mesh_attributes["uvmap"] = mesh.GetTriangleAttr("texture_uvs");

Maybe we want to change this one.
I think the options we have are
triangle_texture_uvs (+valid identifier -multiple underscores)
triangle.texture_uvs (+like accessing an o3d attribute -can be saved to npz but not a valid identifier)
triangle__texture_uvs (+valid identifier -even more _)

More options after TriangleMesh->Mesh
face{_,.,__}texture_uvs

What do you think? @errissa

[benjaminum]

Reviewable status: 0 of 2 files reviewed, 1 unresolved discussion (waiting on @errissa)

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cpp/open3d/t/io/TriangleMeshIO.cpp line 243 at r2 (raw file):

Previously, benjaminum (Benjamin Ummenhofer) wrote…

Maybe we want to change this one.
I think the options we have are
triangle_texture_uvs (+valid identifier -multiple underscores)
triangle.texture_uvs (+like accessing an o3d attribute -can be saved to npz but not a valid identifier)
triangle__texture_uvs (+valid identifier -even more _)

More options after TriangleMesh->Mesh
face{_,.,__}texture_uvs

What do you think? @errissa

The mentioned options apply to all attributes

[errissa]

Reviewable status: 0 of 2 files reviewed, 1 unresolved discussion (waiting on @errissa)

cpp/open3d/t/io/TriangleMeshIO.cpp line 243 at r2 (raw file):

    }
    if (mesh.HasTriangleAttr("texture_uvs")) {
        mesh_attributes["uvmap"] = mesh.GetTriangleAttr("texture_uvs");

Maybe we want to change this one. I think the options we have are triangle_texture_uvs (+valid identifier -multiple underscores) triangle.texture_uvs (+like accessing an o3d attribute -can be saved to npz but not a valid identifier) triangle__texture_uvs (+valid identifier -even more _)

More options after TriangleMesh->Mesh face{_,.,__}texture_uvs

What do you think? @errissa

I thought we might want to change this one. It doesn't fit any other patterns we're using. I think the simplest is triangle_texture_uvs which is consistent with the way we name everything else. I have made the change.

[benjaminum]

Reviewable status: 0 of 3 files reviewed, 1 unresolved discussion