AprilTag ROS Node

Figure 1. RViz display of AprilTag detection outputs on PC

AprilTag is a robust visual fiducial system, which is used in various applications such as Robotics, localization, SLAM, etc. For more information on AprilTag, is is recommended to visit https://april.eecs.umich.edu/software/apriltag and http://wiki.ros.org/apriltag_ros.

This document describes how to install and run AprilTag ROS node in the ROS1 Docker container. It consists of two steps, 1) Install AprilTag library from source, 2) Run AprilTag ROS node with monochrome camera.

Install AprilTag Library

1. Launch the Docker image. For setting up the ROS1 environment on J7, please follow Docker Setup for ROS 1.

   root@tda4vm-sk:~/j7ros_home# ./docker_run_ros1.sh
   

   Before launching docker_run_ros1.sh, remove ‘–rm’ flag in docker run command in it since we need to commit the changes after installing AprilTag library.

2. Clone AprilTag.

   root@j7-docker:~/j7ros_home/ros_ws$ export APRILTAG_SOURCE_DIR=$HOME/j7ros_home/apriltag
   root@j7-docker:~/j7ros_home/ros_ws$ git clone https://github.com/AprilRobotics/apriltag.git $APRILTAG_SOURCE_DIR
   

3. Build and Install AprilTag library.

   root@j7-docker:~/j7ros_home/ros_ws$ cd $APRILTAG_SOURCE_DIR
   root@j7-docker:~/j7ros_home/ros_ws$ cmake -B build -DCMAKE_BUILD_TYPE=Release
   root@j7-docker:~/j7ros_home/ros_ws$ cmake --build build --target install
   

4. Exit docker and update an image from the container’s changes.

   # Check container_id
   root@tda4vm-sk:~/j7ros_home# docker ps --all
   
   # Update Docker image
   root@tda4vm-sk:~/j7ros_home# docker commit container_id j7-ros-noetic:8.4
   

Run April ROS Node

1. Launch the Docker image.

   root@tda4vm-sk:~/j7ros_home# ./docker_run_ros1.sh
   

2. Clone and build AprilTag ROS package.

   root@j7-docker:~/j7ros_home/ros_ws$ mkdir src
   root@j7-docker:~/j7ros_home/ros_ws$ git clone git clone https://github.com/AprilRobotics/apriltag_ros.git src/apriltag_ros
   root@j7-docker:~/j7ros_home/ros_ws$ catkin_make --source src/apriltag_ros
   

3. Launch AprilTag ROS node.

   root@j7-docker:~/j7ros_home/ros_ws$ source devel/setup.bash
   root@j7-docker:~/j7ros_home/ros_ws$ roslaunch apriltag_ros continuous_detection.launch
   

   Note that tags.yaml and settings.yaml can be configurable for tag definition and tag detection algorithm, respectively. A various types of AprilTags can be downloaded from https://github.com/AprilRobotics/apriltag-imgs.

4. Launch USB camera.

   Connect a USB camera to the SK board. Logitech C920 camera is used for test. Since AprilTag ROS node does not support YUV422 format, we update the following line of mono_capture.launch under /opt/robotics_sdk/ros1/drivers/mono_capture/launch:

   <arg name="encoding"               default="bgr8"/> 
   

   Then launch the camera as follows:

   root@j7-docker:~/j7ros_home/ros_ws$ source devel/setup.bash
   root@j7-docker:~/j7ros_home/ros_ws$ roslaunch mono_capture mono_capture.launch
   

   As shown in Figure 1, we can visualize the AprilTag detection outputs along with their poses with respect to the camera using RViz on PC.