VoxelBlockGrid from point cloud for ray_cast

[TJB-99]

Hey there,

I am pretty new to open3d, so let me know if I am going down the wrong path.

I have a point cloud and a bunch of images with intrinsics and extrinsics.
I am trying to compute ray intersects with 3D voxels for all pixels in the images.
The way to do that seems to be with the VoxelBlockGrid.
Therefore I am constructing it as follows from a point cloud.
But the depth image produced by ray_intersect is 0 everywhere and also extracting the point cloud fails.
So I guess I am constructing it wrong.

vbg = o3d.t.geometry.VoxelBlockGrid(
    attr_names=["tsdf", "weight"],
    attr_dtypes=[o3c.float32, o3c.float32],
    attr_channels=[1, 1],
    voxel_size=3.0 / 512,
    block_resolution=16,
    block_count=100000,
)

block_coords = vbg.compute_unique_block_coordinates(pcd=pc_new)
print("block_coords shape: ", block_coords.shape)
extracted_pc = vbg.extract_point_cloud()

extract_point_cloud gives me the following error:

RuntimeError: [Open3D Error] (void open3d::core::HashMap::CheckKeyLength(const open3d::core::Tensor&) const) /root/Open3D/cpp/open3d/core/hashmap/HashMap.cpp:379: Input number of keys should > 0, but got 0.

Any help would be much appreciated!