Quality of service demos in python

[dhood]

Context:
The image_tools demo is used in the “Use quality-of-service settings to handle lossy networks” tutorial. This demo currently only exists for C++. We have since added a python client library for ROS 2.

To do:

• Replicate the image_tools demo using the python client library.

  • using a webcam
  • using synthetic images (useful for running automated tests without having a camera present)

• Incorporate it into the quality of service tutorial.

Pointers:

• This PR has examples of using different QoS profiles in python nodes: https://github.com/ros2/examples/pull/132/files
• This OpenCV tutorial shows how to show images in python: http://docs.opencv.org/3.0-beta/doc/py_tutorials/py_gui/py_image_display/py_image_display.html
• This C++ image_tools demo shows how to list a dependency on OpenCV:

  demos/image_tools/package.xml

  Line 11 in 16c3bc5

  <build_depend>libopencv-dev</build_depend>

[kgreenek]

Was this closed by:
ros2/examples#132
?

[dhood]

Not quite, but they are indeed related. The examples in ros2/examples#132 (e.g. qos_listener_py.py) are quite simple - they just send/receive strings. The demo being referred to here is with images, because it's easier to "feel" the latency in the quality of service demo with a lagging webcam stream than it is to with strings.

[clalancette]

I'm going to take a crack at doing this to get my feet wet.