Differenes between radar point cloud data and processed data

Cubloc · October 24, 2019, 2:54am

Hi,

I use the function ‘RadarPointCloud.from_file(data_path)’ to get radar point cloud with a size(18,125)
Then I use ‘nusc.get_sample_data(radar_data[‘token’])’ and get the processed data.

image.png901×163 5.72 KB

I have thought only some filter was made, but the specific data are completely different, e.g. ‘z’ value, how to understand the difference, and why the latter doesn’t contain velocity information.

Thanks a lot.

holger-motional · October 24, 2019, 2:57am

Take a look at the code:

github.com

nutonomy/nuscenes-devkit/blob/master/python-sdk/nuscenes/nuscenes.py#L210


    sd_record = self.get('sample_data', sample_data_token)
    return osp.join(self.dataroot, sd_record['filename'])


def get_sample_data(self, sample_data_token: str,
                    box_vis_level: BoxVisibility = BoxVisibility.ANY,
                    selected_anntokens: List[str] = None,
                    use_flat_vehicle_coordinates: bool = False) -> \
        Tuple[str, List[Box], np.array]:
    """
    Returns the data path as well as all annotations related to that sample_data.
    Note that the boxes are transformed into the current sensor's coordinate frame.
    :param sample_data_token: Sample_data token.
    :param box_vis_level: If sample_data is an image, this sets required visibility for boxes.
    :param selected_anntokens: If provided only return the selected annotation.
    :param use_flat_vehicle_coordinates: Instead of the current sensor's coordinate frame, use ego frame which is
                                         aligned to z-plane in the world.
    :return: (data_path, boxes, camera_intrinsic <np.array: 3, 3>)
    """


    # Retrieve sensor & pose records
    sd_record = self.get('sample_data', sample_data_token)

“Note that the boxes are transformed into the current sensor’s coordinate frame.”
The velocity isn’t used here. You can however look at the vx/vy values in https://github.com/nutonomy/nuscenes-devkit/blob/master/python-sdk/nuscenes/utils/data_classes.py#L292

Cubloc · October 24, 2019, 7:03am

Thank you for your reply.

By the way, I still have a question, is it possible to make sure the relationship bewteen each radar point and actual object ?

With the function “get_sampe_data”, it’s easy for each point to find the annotation box with tokens, but it lacked velocity information.
To get the velocity information, I have to fetch the point data directly from files. Is there any one-to-one match between these points with boxes?

holger-motional · October 29, 2019, 2:31am

The easiest would probably be to create a copy of get_sample_data that does not throw away the velocity information.