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Node interface

Behavior

  • Upon receiving a camera image, it detects circular markers using the WhyCode algorithm and publishes the marker array.
  • Optionally overlays debug visuals if enabled.
  • Parameters are dynamically reconfigurable via the ROS parameter interface, with validation.
  • Read only parameters are: calib_file, img_transport, img_base_topic, info_topic, id_bits, id_samples, hamming_dist.
  • Calibration information can be loaded from or saved to a YAML file.
  • The default node name is /whycode_node using the whycode_launch.py

Parameters

Name Type Description Default
calib_file string Coordinate calibration file path (Read-only)
img_transport string Subscribed image topic transport type (Read-only) "compressed"
img_base_topic string Base name of the subscribed image topic (Read-only)
info_topic string Camera info topic associated with the image topic (Read-only)
id_bits int Number of encoded bits (Read-only)
id_samples int Number of samples along the perimeter (Read-only) 360
hamming_dist int Encoded ID hamming distance (Read-only) 1
draw_coords bool Draw coordinate systems in debug image true
draw_segments bool Highlight found markers in debug image true
use_gui bool Enable any drawings in debug image true
identify bool Enable WhyCode detection true
coords_method int Coordinates transformation method 0
num_markers int Number of markers to detect 1
min_size int Minimum marker size in pixels 100
circle_diameter double Marker outer diameter in meters 0.122
calib_dist_x double Distance between markers in X direction 1.0
calib_dist_y double Distance between markers in Y direction 1.0
initial_circularity_tolerance double Initial circularity test tolerance (percent) 100.0
final_circularity_tolerance double Final circularity test tolerance (percent) 2.0
area_ratio_tolerance double Tolerance of black and white area ratios (percent) 40.0
center_distance_tolerance_ratio double Concentricity ratio tolerance (percent) 10.0
center_distance_tolerance_abs double Absolute concentricity tolerance (pixels) 5.0

Example CLI Calls

ros2 param set /whycode_node <param-name> <param-value>
ros2 param get /whycode_node <param-name>

Subscribed Topics

Topic Type Description
<img_base_topic> sensor_msgs/msg/Image image_transport input image for processing
<info_topic> sensor_msgs/msg/CameraInfo Associated camera info

Published Topics

Topic Type Description
~/debug_image sensor_msgs/msg/Image image_transport debug image (if GUI enabled)
~/markers whycode_interfaces/msg/MarkerArray Array of detected markers
~/discovery whycode_interfaces/msg/Discovery Discovery signal message

Services

Service Name Type Description
~/set_calib_method whycode_interfaces/srv/SetCalibMethod Select calibration method (AUTO=0, MANUAL=1)
~/set_calib_path whycode_interfaces/srv/SetCalibPath Load or save calibration file (SAVE=0, LOAD=1)
~/select_marker whycode_interfaces/srv/SelectMarker Select marker based on image pixel coordinate

Example CLI Calls

ros2 service call /whycode_node/set_calib_method whycode_interfaces/srv/SetCalibMethod "{method: 0}"  # AUTO
ros2 service call /whycode_node/set_calib_method whycode_interfaces/srv/SetCalibMethod "{method: 1}"  # MANUAL

ros2 service call /whycode_node/set_calib_path whycode_interfaces/srv/SetCalibPath "{action: 0, path: '/path/to/calib.yaml'}"  # SAVE
ros2 service call /whycode_node/set_calib_path whycode_interfaces/srv/SetCalibPath "{action: 1, path: '/path/to/calib.yaml'}"  # LOAD

ros2 service call /whycode_node/select_marker whycode_interfaces/srv/SelectMarker "{point: {x: 100.0, y: 200.0, z: 0.0}}"  # (x,y) px