event_camera_msgs

messages for event based cameras

README

ROS package with messages for event based cameras

This package has definitions for ROS / ROS2 messages created by event based vision sensors. The events are kept in a compact binary format to avoid slow serialization and deserialization during recording.

Event camera messages can be visualized with the event_camera_renderer and converted to other message formats using event_camera_tools.

For encoding and decoding of messages in C++ look at event_camera_codecs. The event_camera_py package provides a module for fast and convenient loading of events in python.

Messages

EventPacket

The EventPacket message contains a packet (array) of events in binary format.

Description of the encodings:

  • evt3: raw Metavision evt3 data as it comes from the SDK. For the details of the encoding scheme refer to the Prophesee Metavision documents.

      The ``time_base`` field is not used and its content is undefined. Recovery of
  sensor time requires decoding the data packets. For more about
  time stamps see documentation in
  [event_camera_codecs](https://github.com/ros-event-camera/event_camera_codecs).

  • libcaer_cmp: compressed libcaer format. The compression is similar to evt3 but the time_base field is used to recover absolute sensor time. The decompression is best understood by looking at the source code here.

  • libcaer: uncompressed messages in the format that libcaer presents it to its upper layers. The encoding takes 64bits per event and is similar to the mono encoding described below. This message format is generally inferior to libcaer_cmp.

  • mono: (deprecated) event messages from the Prophesee cameras. Encodes on 64 bit boundaries as follows:

    bits

    interpretation

    63

    polarity: ON event = 1, OFF event = 0

    48-62

    y (15 bits)

    32-48

    x (16 bits)

    0-32

    dt (32 bits)

    To recover the original sensor time, add the delta dt to the message time_base field. Both dt and time_base are in nanoseconds. To recover the best estimate ROS sensor time stamp add dt to the ROS header stamp.

  • trigger (deprecated): external trigger messages from e.g. the Prophesee Metavision cameras.

    bits

    interpretation

    63

    polarity: ON event = 1, OFF event = 0

    33-62

    unused (31 bits)

    0-32

    dt (32 bits)

    To recover the original sensor time add the delta dt to the message time_base field (in nanoseconds). To recover the best estimate ROS sensor time stamp add dt to the header stamp.

License

This package is released under the Apache-2 license.