Planning Scene ROS API

In this tutorial, we will examine the use of planning scene diffs to perform two operations:

Adding and removing objects into the world

Attaching and detaching objects to the robot

Getting Started

If you haven’t already done so, make sure you’ve completed the steps in Getting Started.

Running the code

Open two shells. In the first shell start RViz and wait for everything to finish loading:

ros2 launch moveit2_tutorials move_group.launch.py

In the second shell, run the launch file for this demo:

ros2 launch moveit2_tutorials planning_scene_ros_api_tutorial.launch.py

After a short moment, the RViz window should appear and look similar to this step in the Visualization Tutorial. To progress through each demo step either press the Next button in the RvizVisualToolsGui panel at the bottom of the screen or select Key Tool in the Tools panel at the top of the screen and then press 0 on your keyboard while RViz is focused.

Expected Output

In RViz, you should be able to see the following:

Object appears in the planning scene.
Object gets attached to the robot.
Object gets detached from the robot.
Object is removed from the planning scene.

The entire code

The entire code can be seen here in the MoveIt GitHub project.

Visualization

The package MoveItVisualTools provides many capabilities for visualizing objects, robots, and trajectories in RViz as well as debugging tools such as step-by-step introspection of a script.

rviz_visual_tools::RvizVisualTools visual_tools("panda_link0", "planning_scene_ros_api_tutorial", node);
visual_tools.loadRemoteControl();
visual_tools.deleteAllMarkers();

ROS API

The ROS API to the planning scene publisher is through a topic interface using “diffs”. A planning scene diff is the difference between the current planning scene (maintained by the move_group node) and the new planning scene desired by the user.

Advertise the required topic

We create a publisher and wait for subscribers. Note that this topic may need to be remapped in the launch file.

rclcpp::Publisher<moveit_msgs::msg::PlanningScene>::SharedPtr planning_scene_diff_publisher =
    node->create_publisher<moveit_msgs::msg::PlanningScene>("planning_scene", 1);
while (planning_scene_diff_publisher->get_subscription_count() < 1)
{
  rclcpp::sleep_for(std::chrono::milliseconds(500));
}
visual_tools.prompt("Press 'next' in the RvizVisualToolsGui window to continue the demo");

Define the attached object message

We will use this message to add or subtract the object from the world and to attach the object to the robot.

moveit_msgs::msg::AttachedCollisionObject attached_object;
attached_object.link_name = "panda_hand";
/* The header must contain a valid TF frame*/
attached_object.object.header.frame_id = "panda_hand";
/* The id of the object */
attached_object.object.id = "box";

/* A default pose */
geometry_msgs::msg::Pose pose;
pose.position.z = 0.11;
pose.orientation.w = 1.0;

/* Define a box to be attached */
shape_msgs::msg::SolidPrimitive primitive;
primitive.type = primitive.BOX;
primitive.dimensions.resize(3);
primitive.dimensions[0] = 0.075;
primitive.dimensions[1] = 0.075;
primitive.dimensions[2] = 0.075;

attached_object.object.primitives.push_back(primitive);
attached_object.object.primitive_poses.push_back(pose);

Note that attaching an object to the robot requires the corresponding operation to be specified as an ADD operation.

attached_object.object.operation = attached_object.object.ADD;

Since we are attaching the object to the robot hand to simulate picking up the object, we want the collision checker to ignore collisions between the object and the robot hand.

attached_object.touch_links = std::vector<std::string>{ "panda_hand", "panda_leftfinger", "panda_rightfinger" };

Add an object into the environment

Add the object into the environment by adding it to the set of collision objects in the “world” part of the planning scene. Note that we are using only the “object” field of the attached_object message here.

RCLCPP_INFO(LOGGER, "Adding the object into the world at the location of the hand.");
moveit_msgs::msg::PlanningScene planning_scene;
planning_scene.world.collision_objects.push_back(attached_object.object);
planning_scene.is_diff = true;
planning_scene_diff_publisher->publish(planning_scene);
visual_tools.prompt("Press 'next' in the RvizVisualToolsGui window to continue the demo");

Interlude: Synchronous vs Asynchronous updates

There are two separate mechanisms available to interact with the move_group node using diffs:

Send a diff via a rosservice call and block until the diff is applied (synchronous update)
Send a diff via a topic, continue even though the diff might not be applied yet (asynchronous update)

While most of this tutorial uses the latter mechanism (given the long sleeps inserted for visualization purposes asynchronous updates do not pose a problem), it would be perfectly justified to replace the planning_scene_diff_publisher by the following service client:

rclcpp::Client<moveit_msgs::srv::ApplyPlanningScene>::SharedPtr planning_scene_diff_client =
    node->create_client<moveit_msgs::srv::ApplyPlanningScene>("apply_planning_scene");
planning_scene_diff_client->wait_for_service();

and send the diffs to the planning scene via a service call:

auto request = std::make_shared<moveit_msgs::srv::ApplyPlanningScene::Request>();
request->scene = planning_scene;
std::shared_future<std::shared_ptr<moveit_msgs::srv::ApplyPlanningScene_Response>> response_future;
response_future = planning_scene_diff_client->async_send_request(request).future.share();

wait for the service to respond

std::chrono::seconds wait_time(1);
std::future_status fs = response_future.wait_for(wait_time);
if (fs == std::future_status::timeout)
{
  RCLCPP_ERROR(LOGGER, "Service timed out.");
}
else
{
  std::shared_ptr<moveit_msgs::srv::ApplyPlanningScene_Response> planning_response;
  planning_response = response_future.get();
  if (planning_response->success)
  {
    RCLCPP_INFO(LOGGER, "Service successfully added object.");
  }
  else
  {
    RCLCPP_ERROR(LOGGER, "Service failed to add object.");
  }
}

Note that this does not continue until we are sure the diff has been applied.

Attach an object to the robot

When the robot picks up an object from the environment, we need to “attach” the object to the robot so that any component dealing with the robot model knows to account for the attached object, e.g. for collision checking.

Attaching an object requires two operations

Removing the original object from the environment
Attaching the object to the robot

/* First, define the REMOVE object message*/
moveit_msgs::msg::CollisionObject remove_object;
remove_object.id = "box";
remove_object.header.frame_id = "panda_hand";
remove_object.operation = remove_object.REMOVE;

Note how we make sure that the diff message contains no other attached objects or collisions objects by clearing those fields first.

/* Carry out the REMOVE + ATTACH operation */
RCLCPP_INFO(LOGGER, "Attaching the object to the hand and removing it from the world.");
planning_scene.world.collision_objects.clear();
planning_scene.world.collision_objects.push_back(remove_object);
planning_scene.robot_state.attached_collision_objects.push_back(attached_object);
planning_scene.robot_state.is_diff = true;
planning_scene_diff_publisher->publish(planning_scene);
visual_tools.prompt("Press 'next' in the RvizVisualToolsGui window to continue the demo");

Detach an object from the robot

Detaching an object from the robot requires two operations

Detaching the object from the robot
Re-introducing the object into the environment

/* First, define the DETACH object message*/
moveit_msgs::msg::AttachedCollisionObject detach_object;
detach_object.object.id = "box";
detach_object.link_name = "panda_hand";
detach_object.object.operation = attached_object.object.REMOVE;

Note how we make sure that the diff message contains no other attached objects or collisions objects by clearing those fields first.

/* Carry out the DETACH + ADD operation */
RCLCPP_INFO(LOGGER, "Detaching the object from the robot and returning it to the world.");
planning_scene.robot_state.attached_collision_objects.clear();
planning_scene.robot_state.attached_collision_objects.push_back(detach_object);
planning_scene.robot_state.is_diff = true;
planning_scene.world.collision_objects.clear();
planning_scene.world.collision_objects.push_back(attached_object.object);
planning_scene.is_diff = true;
planning_scene_diff_publisher->publish(planning_scene);
visual_tools.prompt("Press 'next' in the RvizVisualToolsGui window to continue the demo");

Remove the object from the collision world

Removing the object from the collision world just requires using the remove object message defined earlier. Note, also how we make sure that the diff message contains no other attached objects or collisions objects by clearing those fields first.

RCLCPP_INFO(LOGGER, "Removing the object from the world.");
planning_scene.robot_state.attached_collision_objects.clear();
planning_scene.world.collision_objects.clear();
planning_scene.world.collision_objects.push_back(remove_object);
planning_scene_diff_publisher->publish(planning_scene);