Following Server

Source code on Github.

The Following Server in opennav_following implements a server for following dynamic objects from a detection topic or specific reference frame. This server allows the robot to follow and maintain a determined distance from a detected object or specific frame, using topic-based detection techniques or coordinate frame tracking. The server is designed to be called by a BT application or autonomy application to follow moving objects.

Parameters

controller_frequency

Type	Default
double	50.0

Description: Control frequency (Hz) for the following control loop.

detection_timeout

Type	Default
double	2.0

Description: Timeout (s) to wait for detection of the object to follow.

rotate_to_object_timeout

Type	Default
double	10.0

Description: Timeout (s) to rotate searching for the object when detection is lost.

static_object_timeout

Type	Default
double	-1.0

Description: Timeout (s) to stop following when the object remains static. If -1.0, the robot will follow indefinitely.

linear_tolerance

Type	Default
double	0.15

Description: Linear tolerance (m) to consider that the target position has been reached.

angular_tolerance

Type	Default
double	0.15

Description: Angular tolerance (rad) to consider that the target orientation has been reached.

max_retries

Type	Default
int	3

Description: Maximum number of retries when detection or control fails.

base_frame

Type	Default
string	“base_link”

Description: Robot’s base frame for control law.

fixed_frame

Type	Default
string	“odom”

Description: Fixed frame to use, recommended to be a smooth odometry frame not map.

filter_coef

Type	Default
double	0.1

Description: Filter coefficient for smoothing object pose detections.

desired_distance

Type	Default
double	1.0

Description: Desired distance (m) to maintain from the followed object.

skip_orientation

Type	Default
bool	true

Description: If true, ignore the detected object’s orientation and point toward it from the robot’s position.

search_by_rotating

Type	Default
bool	false

Description: If true, the robot will rotate in place when it loses object detection to try to find it again.

search_angle

Type	Default
double	M_PI_2

Description: Maximum angle (rad) to rotate when searching for the object.

odom_topic

Type	Default
string	“odom”

Description: Odometry topic to use for obtaining the robot’s current velocity.

odom_duration

Type	Default
double	0.3

Description: Time (s) to buffer odometry commands to estimate the robot speed.

transform_tolerance

Type	Default
double	0.1

Description: Time with which to post-date the transform that is published, to indicate that this transform is valid into the future.

Example

following_server:
  ros__parameters:
    controller_frequency: 50.0
    detection_timeout: 2.0
    rotate_to_object_timeout: 10.0
    static_object_timeout: 30.0  # -1.0 for indefinite following
    linear_tolerance: 0.15
    angular_tolerance: 0.15
    max_retries: 3
    base_frame: "base_link"
    fixed_frame: "odom"
    filter_coef: 0.1
    desired_distance: 1.0
    skip_orientation: true
    search_by_rotating: false
    odom_topic: "odom"
    odom_duration: 0.3
    transform_tolerance: 0.1

    # Controller configuration (inherited from docking controller)
    controller:
      k_phi: 3.0
      k_delta: 2.0
      beta: 0.4
      lambda: 2.0
      v_linear_min: 0.1
      v_linear_max: 0.5
      v_angular_max: 1.0
      slowdown_radius: 0.15
      use_collision_detection: false
      transform_tolerance: 0.1