> ## Documentation Index > Fetch the complete documentation index at: https://dragonwingdocs.qualcomm.com/llms.txt > Use this file to discover all available pages before exploring further. # Enable AprilTag pipeline with sample_apriltag > The sample_apriltag is the ROS package to provide AprilTag pipeline samples for Qualcomm robotics platforms. For more information, see [sample\_apriltag](https://github.com/qualcomm-qrb-ros/qrb_ros_samples/edit/main/robotics/sample_apriltag) GitHub repository. Live camera view of AprilTag markers being detected, each overlaid with its tag outline and identifier. ## Pipeline flow for `sample_apriltag` The following figure shows the pipeline flow for `sample_apriltag`. AprilTag pipeline from camera capture through color space conversion and rectification to tag detection and pose output. * The pipeline accepts an NV12 image from `qrb_ros_camera` and converts the color space to RGB8 format. * Then, it uses `image_proc` to rectify the image, and outputs `/image_rect`. * The `Apriltag` node detects tags and calculates their poses, which are published through `/tf`. ## ROS nodes used in the `sample_apriltag` pipeline The following table lists the ROS nodes used in the `sample_apriltag` pipeline and describes what each node does. | ROS Node | Description | | ----------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------- | | [`qrb_ros::camera::CameraNode`](https://github.com/qualcomm-qrb-ros/qrb_ros_camera) | Qualcomm ROS 2 package that captures images with parameters and publishes them to ROS topics. | | [`qrb_ros::colorspace_convert::ColorspaceConvertNode`](https://github.com/qualcomm-qrb-ros/qrb_ros_color_space_convert) | Provides a ROS node to convert image from nv12 to rgb8 format. | | [`image_proc::RectifyNode`](https://github.com/ros-perception/image_pipeline/tree/rolling/image_proc) | Subscribes to unrectified image and Camera calibration metadata to take rectification. | | [`apriltag_ros::AprilTagNode`](https://github.com/christianrauch/apriltag_ros) | This ROS 2 node uses the `AprilTag` library to detect AprilTags in images and publishes their poses, IDs and additional metadata. | ## ROS topics used in the `sample_apriltag` pipeline The following table lists the ROS topics used in the `sample_apriltag` pipeline, with the message type and the node that publishes each topic. | ROS Topic | Type | Published by | | ----------------------- | ------------------------------------------ | ---------------------------------------------------- | | `/apriltag/image_nv12` | `sensor_msgs/msg/Image` | `qrb_ros::camera::CameraNode` | | `/apriltag/camera_info` | `sensor_msgs/msg/CameraInfo.msg` | `qrb_ros::camera::CameraNode` | | `/apriltag/image_rgb8` | `sensor_msgs/msg/Image` | `qrb_ros::colorspace_convert::ColorspaceConvertNode` | | `/apriltag/image_rect` | `sensor_msgs/msg/Image` | `image_proc::RectifyNode` | | `/apriltag/detections` | `apriltag_msgs/msg/AprilTagDetectionArray` | `apriltag_ros::AprilTagNode` | | `/tf` | `tf2_msgs/msg/TFMessage` | `apriltag_ros::AprilTagNode` | ## Prerequisites You have set up the device, installed ROS2 Jazzy and the Qualcomm Intelligent Robotics (QIR) SDK on the device according to [Install the QIR SDK](./install-the-qir-sdk). ## Run out-of-the-box `sample_apriltag` ```bash Add the package repositories theme={null} sudo add-apt-repository ppa:ubuntu-qcom-iot/qcom-ppa sudo add-apt-repository ppa:ubuntu-qcom-iot/qirp sudo apt update ``` ```bash Install the packages theme={null} sudo apt install ros-jazzy-sample-apriltag ``` ```bash Start the pipeline theme={null} export XDG_RUNTIME_DIR=/run/user/1000 export WAYLAND_DISPLAY=wayland-1 sudo systemctl start weston-autostart.service source /opt/ros/jazzy/setup.bash ros2 launch sample_apriltag sample_apriltag.launch.py ``` | `tagStandard41h12: 1` | `tagStandard41h12: 2` | `tagStandard41h12: 3` | | 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| | AprilTag marker from the tagStandard41h12 family encoding identifier 1. | AprilTag marker from the tagStandard41h12 family encoding identifier 2. | AprilTag marker from the tagStandard41h12 family encoding identifier 3. | a. Start a terminal and run the following commands to check the apriltag detection result. ```bash theme={null} (ssh) export ROS_DOMAIN_ID=123 (ssh) ros2 topic echo /apriltag/detections ``` The pipeline outputs the detection results with `/apriltag/detections` and detects the tag pose with `/tf`. b. To check the topic output, run the following command: ```bash theme={null} (ssh) ros2 topic echo /apriltag/detections ``` **Result:** ```yaml Output theme={null} header: stamp: sec: 1756288539 nanosec: 411482784 frame_id: stream1_2625 detections: - family: tagStandard41h12 id: 1 hamming: 0 goodness: 0.0 decision_margin: 153.66729736328125 centre: x: 595.2331201546427 y: 382.94486450729545 ... ``` The result shows the detected tag: `tagStandard41h12` and the tag ID is `1`. ## Build from the source of `sample_apriltag` Build `sample_apriltag` from source when you need to change the sample code. The device steps install the dependencies, clone the source repository, and build the package. ### Device steps ```bash Install the dependencies theme={null} sudo apt install ros-dev-tools \ ros-jazzy-image-proc \ ros-jazzy-apriltag-ros \ ros-jazzy-qrb-ros-camera \ ros-jazzy-qrb-ros-colorspace-convert ``` ```bash Clone the sample repository theme={null} mkdir -p ~/qrb_ros_sample_ws/src && cd ~/qrb_ros_sample_ws/src source /opt/ros/jazzy/setup.bash git clone https://github.com/qualcomm-qrb-ros/qrb_ros_samples.git ``` ```bash Build the sample theme={null} cd ~/qrb_ros_sample_ws/src/qrb_ros_samples/robotics/sample_apriltag colcon build --packages-up-to sample_apriltag source install/setup.bash ``` Run and test according to steps 2-4 of [Run out-of-the-box sample\_apriltag](./enable-apriltag-pipeline-with-sample-apriltag#run-out-of-the-box-sample_apriltag).