Python NatNet Client

Python client for Optitrack NatNet streams.

Installation

Install this package via pip:

pip install git+https://github.com/TimSchneider42/python-natnet-client

Usage

The following example highlights the basic usage of this package:

import time

from natnet_client import DataDescriptions, DataFrame, NatNetClient


def receive_new_frame(data_frame: DataFrame):
    global num_frames
    num_frames += 1


def receive_new_desc(desc: DataDescriptions):
    print("Received data descriptions.")


num_frames = 0
if __name__ == "__main__":
    streaming_client = NatNetClient(server_ip_address="127.0.0.1", local_ip_address="127.0.0.1", use_multicast=False)
    streaming_client.on_data_description_received_event.handlers.append(receive_new_desc)
    streaming_client.on_data_frame_received_event.handlers.append(receive_new_frame)

    with streaming_client:
        streaming_client.request_modeldef()

        for i in range(10):
            time.sleep(1)
            streaming_client.update_sync()
            print(f"Received {num_frames} frames in {i + 1}s")

In this example, we first instantiate NatNetClient with the connection parameters and attach one callback function to each of its events. The streaming_client.on_data_description_received_event event is triggered whenever a new data description packet arrives, while the streaming_client.on_data_frame_received_event event is triggered on each incoming data frame. For the configuration of the NatNet server, please refer to the official documentation.

You can process data synchronously, as in this example, by calling streaming_client.update_sync() in your run loop. Alternatively, you can call streaming_client.run_async() once after connecting, which will handle data asynchronously in two additional threads.

We then use the streaming_client instance as a context manager, which is equivalent to calling streaming_client.connect() (and streaming_client.shutdown() afterwards). After the client has been connected, we request the model definitions from the server, which causes it to send a data description packet. Note that data frames do not have to be explicitly requested, but are continuously streamed once a connection has been established.

Apart from requesting model definitions, the NatNetClient class allows sending arbitrary commands to the NatNet server via the send_command and send_request functions. For a list of different commands and requests, please refer to the official documentations.

Notes

As of Motive version 2.3, the marker positions of rigid bodies are only transmitted correctly if "Y-up" is selected in the streaming pane. If "Z-up" is selected, the frame of the rigid bodies is rotated but the marker positions are not, resulting in wrong positions of the markers relative to the rigid body.