ros2_numpy

This project is a fork of ros_numpy to work with ROS 2. It provides tools for converting ROS messages to and from numpy arrays. In the ROS 2 port, the module has been renamed to ros2_numpy. Users are encouraged to update their application code to import the module as shown below.

ROS 2:

import ros2_numpy as rnp

ROS 1:

import ros_numpy as rnp

Prefacing your calls like rnp.numpify(...) or rnp.msgify(...) should help future proof your codebase while the ROS 1 and ROS 2 ports are API compatible.

The ROS 2 port has been bootstrapped as version 2.0.3. The MAJOR version has been set to 2 to indicate ROS 2 and the MINOR and PATCH versions match the ROS 1 version from which the ROS 2 port was bootstrapped. The reasoning behind this is to allow for creating tags in this fork that can be released into the ROS 2 distribution while not conflicting with existing tags on the upstream repository. A release into Foxy is still pending.

This module contains two core functions:

• arr = numpify(msg, ...) - try to get a numpy object from a message
• msg = msgify(MessageType, arr, ...) - try and convert a numpy object to a message

Currently supports:

• sensor_msgs.msg.PointCloud2 ↔ structured np.array:

  data = np.zeros(100, dtype=[
    ('x', np.float32),
    ('y', np.float32),
    ('vectors', np.float32, (3,))
  ])
  data['x'] = np.arange(100)
  data['y'] = data['x']*2
  data['vectors'] = np.arange(100)[:,np.newaxis]
  
  msg = ros2_numpy.msgify(PointCloud2, data)

  data = ros2_numpy.numpify(msg)
  

• sensor_msgs.msg.LaserScan ↔ structured np.array

• sensor_msgs.msg.Image ↔ 2/3-D np.array, similar to the function of cv_bridge, but without the dependency on cv2

• nav_msgs.msg.OccupancyGrid ↔ np.ma.array

• geometry.msg.Vector3 ↔ 1-D np.array. hom=True gives [x, y, z, 0]

• geometry.msg.Point ↔ 1-D np.array. hom=True gives [x, y, z, 1]

• geometry.msg.Quaternion ↔ 1-D np.array, [x, y, z, w]

• geometry.msg.Transform ↔ 4×4 np.array, the homogeneous transformation matrix

• geometry.msg.Pose ↔ 4×4 np.array, the homogeneous transformation matrix from the origin

Support for more types can be added with:

@ros2_numpy.converts_to_numpy(SomeMessageClass)
def convert(my_msg):
    return np.array(...)

@ros2_numpy.converts_from_numpy(SomeMessageClass)
def convert(my_array):
    return SomeMessageClass(...)

Any extra args or kwargs to numpify or msgify will be forwarded to your conversion function

Future work

• Add simple conversions for:

  • geometry_msgs.msg.Inertia