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How to do visual servoing with Parrot Bebop 2 drone using visp_ros

Introduction

This tutorial explains how to use visp_ros package to do visual servoing with the Parrot Bebop 2 drone.

You can see the program in action in this video :

Prerequisites

• Parrot Bebop 2 drone

• An April Tag from 36h11 family that will serve as target for the visual servoing (see this page to print one).

• Modified version of bebop_autonomy package

In order to control the drone, the ROS wrapper bebop_autonomy is required. However, this wrapper doesn't implement a way to send relative move commands to the drone.

We have added the necessary modifications in this fork.

You have to install bebop_autonomy from fork manually :

• $ cd ~/catkin_ws/src
  $ git clone https://github.com/lagadic/bebop_autonomy.git
  $ cd bebop_autonomy/
  $ git checkout inria-moveby
  $ cd ~/catkin_ws
  $ rosdep update
  $ rosdep install --from-paths src -i
  $ catkin_make
  $ source ~/catkin_ws/devel/setup.bash

Build visp_ros from source

Note that visp_ros package has a dependency with ros-<distro>-visp_bridge and ros-<distro>-visp packages. Since ros-<distro>-visp package corresponds to ViSP 3.2.0 that is too old for visp_ros package, you need to install ViSP from source as well as ros-<distro>-visp_bridge.

To install ViSP from source, proceed as described in this [tutorial](file:///home/fspindle/visp_ws/visp/visp-build/doc/html/tutorial-install-ubuntu.html#install_ubuntu_quick).

Create first a workspace:

• $ echo "export VISP_WS=$HOME/visp-ws" >> ~/.bashrc
  $ source ~/.bashrc
  $ mkdir -p $VISP_WS

Install a small number of recommended 3rd parties

• $ sudo apt-get install libopencv-dev libx11-dev liblapack-dev libeigen3-dev libdc1394-22-dev libv4l-dev libzbar-dev libpthread-stubs0-dev libjpeg-dev libpng-dev libdmtx-dev

Get ViSP source code

• $ cd $VISP_WS
  $ git clone https://github.com/lagadic/visp.git

Create a build folder and build ViSP

• $ mkdir -p $VISP_WS/visp-build
  $ cd $VISP_WS/visp-build
  $ cmake ../visp
  $ make -j4

Set VISP_DIR environment variable

• $ echo "export VISP_DIR=$VISP_WS/visp-build" >> ~/.bashrc
  $ source ~/.bashrc

Now get vision_visp package: ` $ cd ~/catkin_ws/src $ git clone https://github.com/lagadic/vision_visp.git `

To build visp_ros package from source run:

• $ cd ~/catkin_ws/src
  $ git clone https://github.com/lagadic/visp_ros.git
  $ cd ~/catkin_ws
  $ catkin_make -DVISP_DIR=${VISP_DIR}
  $ source ~/catkin_ws/install/setup.bash

Running the program

visp_ros contains two launch files (launch/bebop_servo_node.launch and launch/bebop_servo_nodelet.launch) that allow to start the program. Both start two processes : the drone driver and the visual servoing program, with the necessary remappings. One uses regular nodes, and one uses nodelets (more efficient than nodes to transmit image data, see this page for more details on nodelets).

There are also some parameters you need to adapt to your current task :

• The tag size (default : 0.14 meters)
• The desired distance to the tag (default : 1.5 meter)
• The orientation of the camera (default : -15 degrees for tilt and 0 degree for pan)

Once everything is set up, you can launch the program :

• $ roslaunch visp_ros bebop_servo_node.launch

or

• $ roslaunch visp_ros bebop_servo_nodelet.launch

• $ roslaunch visp_ros bebop_servo_nodelet.launch ip:=192.168.43.1

The drone driver will start, as well as the visual servoing program, that takes images from the drone camera as input, computes displacement commands, and sends them to the drone.

To make the drone take off and start the servoing, use (in another terminal) :

• $ rostopic pub --once /bebop/takeoff std_msgs/Empty

To make the drone land, use :

• $ rostopic pub --once /bebop/land std_msgs/Empty

Understanding the program

If you need more details on how the visual servoing program works, check the version in the open-source library ViSP : Tutorial: Visual-servoing with Parrot Bebop 2 drone.