14.3. AprilTag ROS Node

Figure 1. RViz display of AprilTag detection outputs on PC

AprilTag is a robust visual fiducial system used in various applications such as Robotics, localization, and SLAM. For more information on AprilTag, it 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 the AprilTag ROS node in the ROS 1 Docker container. It consists of two steps:

1. Install the AprilTag library from source.

2. Run the AprilTag ROS node with a monochrome camera.

14.3.1. Install AprilTag Library

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

   root@am6x-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@am6x-sk:~/j7ros_home# docker ps --all
   
   # Update Docker image
   root@am6x-sk:~/j7ros_home# docker commit container_id j7-ros-noetic:8.6
   

14.3.2. Run April ROS Node

1. Launch the Docker image.

   root@am6x-sk:~/j7ros_home# ./docker_run_ros1.sh
   

2. Clone and build the 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 the 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.