checkerboard_detector

../../_images/checkerboard_detector.png

checkerboard_detector is an executable to detect checker board. You can find marker pattern in jsk-ros-pkg/calibboard_sheet.

Subscribing Topics

  • image (sensor_msgs/Image)

  • camera_info (sensor_msgs/CameraInfo)

    Input image and camera info. Intrinsic camera parameter is acquired from camera_info.

  • Image (sensor_msgs/Image)

  • CameraInfo (sensor_msgs/CameraInfo)

    These topics are deprecated.

Publishing Topics

  • ObjectDetection (posedetection_msgs/ObjectDetection)

  • objectdetection_pose (geometry_msgs/PoseStamped)

    Pose of checkerboard in posedetection_msgs/ObjectDetection and geometry_msgs/PoseStamped.

  • corner_point (geometry_msgs/PointStamped)

    Corner points.

  • polygons (jsk_recognition_msgs/PolygonArray)

    Publish checker board as jsk_recognition_msgs/PolygonArray. It is useful to visualize in rviz.

  • debug_image (sensor_msgs/Image)

    Debug image showing detected checker board.

Parameters

  • display (Int, default: 0)

    Set 1 to enable debug view (not image_view but OpenCV window). Note that debug_image is published even when this parameter is set to 0.

  • board_type (String, default: chess)

    Type of marker. chess, circle, circles, acircle and acircles are supported. circle and circles are the same, and also acircle and acircles are.

  • rect%d_size_x (Float, required)

  • rect%d_size_y (Float, required)

    Size of checkerboard in meters, where %d means index of checker board starting from 0.

  • grid%d_size_x (Int, required)

  • grid%d_size_y (Int, required)

    The number of grids along x and y axis.

  • type%d (String, default: checker%dx%d)

    Name of checker board written to objects/type field in ObjectDetection topic.

  • maxboard (Int, default: -1)

    Maximum number of checker board. -1 means infinity, so this node wil detect as much as possible.

  • use_P (Bool, default: false)

    By default, use camera matrix (K) and unrectified image (image_raw). If you use rectified image (image_rect), use_P should be true.

  • invert_color (Bool, default: false)

    Invert white and black before searching cross points or circles.

  • message_throttle (Int, default: 1)

    Finding checker boards every message_throttle images

  • frame_id (String, default: "")

    Frame ID written to ObjectDetection topic header. If empty string is specified, frame_id of image topic will be used.

  • queue_size (Int, default: 1)

  • publish_queue_size (Int, default: 1)

    Size of queue of subscriber is queue_size, publisher is publish_queue_size.

  • axis_size (Float, default: 0.05)

  • circle_size (Int, default: 6)

    For setting displayed marker size. Set circle_size in [pixel]. Set axis_size in [m].

  • verbose (Int, default: 1)

    Output information about input image, number of detected checker board and elapsed time as ROS_INFO if this parameter is greater than 0.

Sample

roslaunch checkerboard_detector sample_checkerboard_detector.launch

Trouble Shooting

  • Q. Estimated checker board pose is not correct

    A. First check debug image and all the detected corner points correctly superimposed on camera view.

    • If the detected corner points is not correct, you need to modify checker board grid size (grid_size parameters).
    • If the detected corner points is correct, confirm checker board size (rect_size parmaeters) and intrinsic camera paramter is calibrated well.

  • Q. How many number of grids better?

    A. I strongly recomment to choose oddxeven or evenxodd. Because if you choose oddxodd or evenxeven, detector will have two potential poses.