ar_land

A ROS package for autonomously landing a quadrocopter (Crazyflie 2.0) using ArUco markers.

The system obtains an image from a wireless camera attached to the Crazyflie 2.0, the image is deinterlaced and the distortion is removed. Once the image is ready, the ar_sys package is used for Aruco marker detection and the relative 3D pose of the Crazyflie to the marker is estimated and published. A Flatness based approach is used for position control of the quadrocopter. A trajectory planner plans a trajectory, which considers the model of the quadrocopter.

For former work see ar_nav.

Required hardware

• Crazyflie 2.0 with a wireless camera attached to the bottom.
• global positioning system that delivers the pose of the drone (we used an OptiTrack system)

Dependencies (non-native)

This package relies on several ROS packages:

• usb_cam: The usb_cam package interfaces with standard USB cameras and publish the images as a sensor_msgs.

• tud_img_prep: The tud_image_prep package is a set of tools for processing camera images with techniques that include deinterlace of analog images and filtering.

• ar_sys: For Aruco marker 3D pose estimation. In essence this can be replaced by any other marker.

• crazyflie_ros: Official package for sending commands and receiving sensor information from the Crazyflie 2.0. The package contains core drivers to use the Crazyflie with ROS, a URDF model of the quadrotor, a simple navigation to goal if it knows the external position and different demos ready to run for Crazyflie.

• vrpn_client_ros: Package for receiving the pose delivered by the optical tracking system.

In the src directory of your ROS catking workspace:

cd ~\catkin_ws\src

Install required oficial ROS packages:

sudo apt-get install ros-kinetic-usb-cam 

Clone all the necessary packages:

git clone https://github.com/raultron/tud_img_prep.git

git clone -b kinetic-devel https://github.com/raultron/ar_sys.git

git clone https://github.com/whoenig/crazyflie_ros.git
cd crazyflie_ros
git submodule init
git submodule update

Use catkin_make on your workspace to compile.

The other packages should be in your ROS distribution.

Also the custom firmware for the crazyflie is required:

• crazyflie_firmware: branch dev_get_full_state_estimate

Optional Dependencies

• image_proc: Image rectification, this package contains the image_proc node that removes camera distortion from the raw image stream, and if necessary will convert Bayer or YUV422 format image data to color. (it is assumed a proper camera calibration using ROS camera_calibration package or any other external tool) Usefull for camera with lense with not too much distortion.

Usage

Print the marker board provided in the data folder. Use a calibrated printer so the markers have the correct measurement.

Our board configurations are named after the robots of our lab (we attach the marker boards on top of them).

C3PO:

• Top Left corner: ID0
• Top Right corner: ID1
• Bottom Left corner: ID2
• Bottom Right corner: ID3
• Aruco marker Side length = 16 cm
• Separation Between Markers = 2 cm
• Coordinate system = located in the center of the marker. Holding the marker board in your hands and looking straigth to it with ID0 on the top left corner: X axis right, Y axis up and Z axis coming out of the marker plane.
• Yaml file for ar_sys: board_c3po.yml

Wide-Angle-Lense Camera Calibration

For the calibration of the Fx797T shutter cam we provide a python script to get the camera parameters. The ROS package camera_calibration GUI and documentation might be helpful to get good images. Put them in a folder an run the calibrate.py script from data inside.