ROS interfaces

The toolbox provides interfaces to ROS – an important framework for robotics and connecting to the physical world through sensors and actuators.

The ROS interface allows you to read images, point clouds and other message from ROS bag files or published topics from a running ROS system.

Reading a ROS bag file

We can

>>> from machinevisiontoolbox import ROSBag
>>> bag = ROSBag('test_ros1.bag')
!! ImportError: rosbags is required for ROS bag support. Install it with: pip install rosbags or pip install machinevision-toolbox-python[ros] [ERR unknown:15:unknown (source/ros.rst)]
>>> bag.print()
!! NameError: name 'bag' is not defined [ERR unknown:15:unknown (source/ros.rst)]
>>> bag = ROSBag('test_ros2.bag', topicfilter="camera")
!! ImportError: rosbags is required for ROS bag support. Install it with: pip install rosbags or pip install machinevision-toolbox-python[ros] [ERR unknown:15:unknown (source/ros.rst)]

Subscribing/publishing to a ROS message stream

This is similar to reading a ROS bag file, but instead of reading from a file we read from a running ROS system. For example, to subscribe to a topic called /camera/image that publishes images:

.. important::

You need to have ROS installed and running with a rosbridge2 node in order to use this feature. The toolbox supports both ROS1 and ROS2, but you need to have the appropriate version of ROS installed and sourced in your environment. rosbridge

from machinevisiontoolbox import ROSTopic

with ROSTopic(“/camera/image”, “/msg/sensor_msgs/Image”) as camera:

for image in camera:

print(image)

Synchronizing messages from multiple topics

Some ROS publishers publish related information on multiple topics, for example a RealSense camera might publish RGB images on one topic and Depth images on another topic. The toolbox provides a convenient interface to read these related messages together using the ROSTopic source. For example, to read images from a topic called /camera/rgb and the corresponding camera info from a topic called /camera/depth:

from machinevisiontoolbox import ROSTopic, SyncROSStreams, Image

rgb = ROSTopic("/camera/rgb", "/msg/sensor_msgs/Image", blocking=True)
depth = ROSTopic("/camera/depth", "/msg/sensor_msgs/Image", blocking=True)
with SyncROSStreams("/camera/rgb", "/camera/depth", tol=20e-3) as rgbd:
     for rgb_msg, depth_msg in rgbd:
        # rgb_msg and depth_msg are both Image instances and emitted
        # by the publisher at the same time step
        print(rgb_msg)

Publishing a ROS message

A ROSTopic instance can also be used to publish messages on a ROS topic. For example, to periodically publish an image to a topic called /camera/rgb:

from machinevisiontoolbox import ROSTopic
from time import sleep
img = Image.Read("monalisa.png")
camera = ROSTopic("/camera/rgb", "/msg/sensor_msgs/Image") # connect to topic
for _ in range(10):
    camera.publish(img)
    sleep(0.1)

For compressed image message types the image will be automatically compressed before publishing, and decompressed when reading.

The argument to ROSTopic.publish can be an Image, a PointCloud or a dict containing elements of a general message.