When Saving and Loading VoxelBlockGrid negative indices cause a Seg Fault

[jmirenzi]

Checklist

• I have searched for similar issues.
• For Python issues, I have tested with the latest development wheel.
• I have checked the release documentation and the latest documentation (for main branch).

Describe the issue

I am working with the tensor implementation of the Voxel Block Grid and I have successfully built a voxel block grid of an object with a series of depth images but when I try to save and load the object I get errors.

The object saves without error but gives this output when loading which is a series of errors about the a negative index outside of the bounds. Then when I try to use the object and call ray_cast there is a Segmentation fault.

Steps to reproduce the bug

//This is the function I use to build and save the Voxel Block Grid

void create_npz_object_from_mesh(open3d::t::geometry::TriangleMesh mesh,std::string out_file_name, bool create_snapshot_files){
    float voxel_size = 3.0/512;
    int block_res = 8;
    int64_t block_count = 6000;
    auto mesh_points_ptr = mesh.ToLegacy().SamplePointsUniformly(5000);
    auto pc_ptr = open3d::t::geometry::PointCloud::FromLegacy(mesh_points_ptr->points_,open3d::core::Dtype::Float32,open3d::core::Device("CUDA:0"));
    open3d::t::geometry::VoxelBlockGrid voxel_grid({"tsdf","weight"},{open3d::core::Dtype::Float32,open3d::core::Dtype::Float32},
                                                        {{1},{1}},voxel_size,block_res,block_count,open3d::core::Device("CUDA:0"));
    
    // Camera Specific; May need to be changed for different objects
    auto camera_intrin = open3d::core::Tensor(std::vector<float>{200.0, 0.0, 150.0,0, 200, 150,0, 0, 1},{3,3}).To(open3d::core::Dtype::Float64); int img_width_height = 300;
    // Transform matrix of 1.5m in the z
    Eigen::Matrix4f transform_mat = Eigen::Matrix4f::Identity();
    Eigen::Quaternionf q;
    transform_mat(2, 3) = 1.5f; // Sets distance between virtual camera and object
    open3d::core::Tensor extrinsic_cam_mat;
    float step_size = M_PI/10;
    for (float r_x=0;r_x<(2*M_PI-step_size);r_x+=step_size){
        for (float r_y=0;r_y<(M_PI-step_size);r_y+=step_size){
            q = Eigen::Quaternionf(Eigen::AngleAxisf(r_x, Eigen::Vector3f::UnitX()) *
                                Eigen::AngleAxisf(r_y, Eigen::Vector3f::UnitY()));
            transform_mat.block<3, 3>(0, 0) = q.toRotationMatrix();
            extrinsic_cam_mat = open3d::core::eigen_converter::EigenMatrixToTensor(transform_mat).To(open3d::core::Dtype::Float64);
            // Note only looking 3m deep when 1.5m away from the object
            
            auto depth_img = pc_ptr.ProjectToDepthImage(img_width_height,img_width_height,camera_intrin,extrinsic_cam_mat); 
            auto block_coords = voxel_grid.GetUniqueBlockCoordinates(depth_img,camera_intrin,extrinsic_cam_mat);
            voxel_grid.Integrate(block_coords,depth_img,camera_intrin,extrinsic_cam_mat);
        }
    }
    voxel_grid.Save(out_file_name);
    return;
}

//But when I run 

std::shared_ptr<open3d::t::geometry::VoxelBlockGrid> voxel_grid = std::make_shared<open3d::t::geometry::VoxelBlockGrid>();
voxel_grid->Load("file_name.npz")

Error message

load_output.txt

Expected behavior

No response

Open3D, Python and System information

- Operating system: Ubuntu 20.04
- Open3D version: 0.18.0
- System architecture: arm64
- Is this a remote workstation?: yes
- How did you install Open3D?: build from source
- Compiler version (if built from source): gcc 9.4.0

Additional information

No response