This package provides services which make object detection more convenient.

The main service provided by this package performs the following:

• Grabs a recent point could from a sensor_msgs/PointCloud2 source
• Transforms the received cloud into the base_link frame

• Extracts objects and surfaces using rail_pcl_object_segmentation

• Names each object and surface, publishes them to various topics, and informs MoveIt's Planning Scene of the results

• Returns the named objects

Services

Object Discovery - provided by discover_objects_server

This is the highest-level service which provides the most convenience for discovering objects. This service implements the entire workflow listed above. The discover_objects_server service processes messages of the type DiscoverObjects.srv.

Updating the Planning Scene - provided by update_environment_service

This service encapsulates the process of naming object and surface point clouds, publishing them to various ros topics, clearing the state of MoveIt's Planning Scene, and adding all discovered objects and surfaces to the Planning Scene.

Launch Files

object_discovery.launch

This launch file is the recommended way to start the object discovery service.

The following nodes are always started:

• discover_objects_server

• extract_objects from rail_pcl_object_segmentation

• cluster_bounding_box_finder_server.py from object_manipulator

The following nodes are only started when updating the environment is enabled:

• update_environment_service

Arguments

 update_state_cloud_timestamps  (boolean, default=true)

• Point clouds may be received which are too old to compute a tf transformation for. If this flag is true, the latest available transformation will be used when this occurs; otherwise, a service call will fail.

 update_environment  (boolean, default=true)

• When true, the discovered objects will be given string names and be published such that planning_environment is made aware of them. Note that any/all objects tracked by planning_environment will be cleared during a discover_objects service request.

 sensor_topic  (string, default=/xtion/depth_registered/points)

• The topic on which the discover_objects service will wait for a sensor_msgs/PointCloud2 message when a service request is received.

 target_frame_id  (string, default=/odom)

• The tf frame which the received sensor_msgs/PointCloud2 should be transformed into before extracting objects.

Nodes

discover_objects_server

This node provides an implementation of the DiscoverObjects.srv service.

Parameters

 ~/sensor_topic  (string)

• The topic on which to wait for a sensor_msgs/PointCloud2 to arrive from when a service request is received.

 ~/target_frame_id  (string)

• The tf frame to transform a received sensor_msgs/PointCloud2 message in to before extracting objects from it.

 ~/service_name  (string, default="discover_objects")

• The name under which this service should appear in ROS.

 ~/extract_objects_service_name  (string, default="extract_objects")

• The name of the service to use for extracting objects from a point cloud. This service must conform to ExtractObjects.srv as defined in rail_pcl_object_segmentation.

 ~/update_environment  (boolean, default=true)

• If true, an UpdateEnvironment.srv request will be delivered to the service at the name specified by ~/update_environment_service_name.

 ~/update_environment_service_name  (string, default="update_environment")

• Defines the name at which to send requests to update MoveIt's Planning Scene with object information, if enabled.

 ~/update_old_cloud_timestamps  (boolean, default=false)

• In the event that a point cloud is received which is too old to process a tf transformation for, this flag determines whether to use the latest available transformation or throw an error. If true, the latest available transform is used; otherwise, the affected service request fails with an error.

update_environment_service

This node provides an implementation of the UpdateEnvironment.srv service.

Parameters

 ~/service_name  (string, default="update_environment")

• The name under which this service should appear in ROS.

 ~/bounding_box_service_name  (string, default="find_cluster_bounding_box2")

• The name at which a bounding box service which fulfills the object_manipulation_msgs FindClusterBoundingBox2.srv interface can be called.

 ~/output/collision_object_topic_name  (string, default="collision_object")

• The name of the topic to publish collision object messages suitable for consumption by MoveIt's Planning Scene.

Using This Package

Make sure a depth camera is generating point clouds. Determine if you need to change any of the default parameters of the object detection, then launch it with those arguments:

roslaunch rail_object_discovery object_detection.launch

When you wish to extract objects, call the /discover_objects service with the desired constraints. Here are some example ones:

rosservice call /discover_objects "constraints:
object_min_sensor_range: 0.2
  object_max_sensor_range: 4.0
  object_min_spherical_radius: 0.01
  object_max_spherical_radius: 0.1
plane_slope_tolerance: 2.0"

Alternately, you can run the extract_objects.sh script included in the package, which uses the constraints in the above example.

rosrun rail_object_detection extract_objects.sh

If you wish to view the extracted objects in rviz without using MoveIt, you can view each extracted object and plane cloud separately by making a PointCloud2 display for each of them. The objects are published to /extract_objects/object_# and the planes are published to /extract_objects/plane_#, where # is 0-9.

Furthermore, a file called vision.rviz is included in the extra/ folder. If you paste its contents into an rviz configuration file, it will add a group of displays for vision-related topics, including Images for the rgb and depth images of the camera, PointCloud2s for the camera and each extracted object and plane, and a MarkerArray which displays the name of each object above its center.