Draco Data Compression on Lidar

Shilpa_Chaturvedi · December 5, 2019, 9:26am

Hi

I am trying to run Draco ( link : https://github.com/google/draco ) compression algorithm on Lidar part of Nuscenes dataset. However the lidar files are provided is pcd.bin file format.

Is there any way to convert .pcd.bin files to ply file format (Polygon File Format) ? As Draco works with ply file format.

Thanks,

holger-motional · December 9, 2019, 3:25am

Hi, we don’t provide a converter, but our data is really just a numpy error, which we found out is the most efficient format for loading. You can load the lidar pointclouds with

        scan = np.fromfile(file_name, dtype=np.float32)
        points = scan.reshape((-1, 5))[:, :4]
        return points.T

Then you can write your own tool to export to ply.

Shilpa_Chaturvedi · January 8, 2020, 10:08am

Thank you for the reply.

I understand that pcd.bin file is created by removing header information from .pcd lidar files. Can you please let me know where can I find header information like how many fields are present in this file.

Thanks in advance.

holger-motional · January 8, 2020, 10:23am

Hi, please take a look at the code that loads them:

github.com

nutonomy/nuscenes-devkit/blob/master/python-sdk/nuscenes/utils/data_classes.py#L247


def nbr_dims() -> int:
    """
    Returns the number of dimensions.
    :return: Number of dimensions.
    """
    return 4


@classmethod
def from_file(cls, file_name: str) -> 'LidarPointCloud':
    """
    Loads LIDAR data from binary numpy format. Data is stored as (x, y, z, intensity, ring index).
    :param file_name: Path of the pointcloud file on disk.
    :return: LidarPointCloud instance (x, y, z, intensity).
    """


    assert file_name.endswith('.bin'), 'Unsupported filetype {}'.format(file_name)


    scan = np.fromfile(file_name, dtype=np.float32)
    points = scan.reshape((-1, 5))[:, :cls.nbr_dims()]
    return cls(points.T)

“Loads LIDAR data from binary numpy format. Data is stored as (x, y, z, intensity, ring index).”

Shilpa_Chaturvedi · January 8, 2020, 4:25pm

Thanks for the immediate response.

Are there standard library to convert pcd to ply format ? Also what are standard LIDAR data formats ?

Thanks.

holger-motional · January 9, 2020, 2:00am

PCD is a standard format, so there should be a number of libraries. I suggest to google it. I think it is good enough for lidar. The reason we used the binary numpy format was that it is the fastest to load in Python.