Initialization and Global Variables¶

In this exercise, we will take a first look at the main application "pick_and_place_node.cpp", its public variables, and how to properly initialize it as a ros node.

Application Variables¶

In QT, open

[Source directory]/collision_avoidance_pick_and_place/include/collision_avoidance_pick_and_place/pick_and_place_utilities.h

The c++ class 'pick_and_place_config' defines public global variables used in various parts of the program. These variables

    ARM_GROUP_NAME  = "manipulator";
    TCP_LINK_NAME   = "tcp_frame";
    MARKER_TOPIC = "pick_and_place_marker";
    PLANNING_SCENE_TOPIC = "planning_scene";
    TARGET_RECOGNITION_SERVICE = "target_recognition";
    MOTION_PLAN_SERVICE = "plan_kinematic_path";
    WRIST_LINK_NAME = "ee_link";
    ATTACHED_OBJECT_LINK_NAME = "attached_object_link";
    WORLD_FRAME_ID  = "world_frame";
    HOME_POSE_NAME  = "home";
    WAIT_POSE_NAME  = "wait";
    AR_TAG_FRAME_ID    = "ar_frame";
    GRASP_ACTION_NAME = "grasp_execution_action";
    BOX_SIZE        = tf::Vector3(0.1f, 0.1f, 0.1f);
    BOX_PLACE_TF    = tf::Transform(tf::Quaternion::getIdentity(), tf::Vector3(-0.8f,-0.2f,BOX_SIZE.getZ()));
    TOUCH_LINKS = std::vector<std::string>();
    RETREAT_DISTANCE  = 0.05f;
    APPROACH_DISTANCE = 0.05f;

In the main program ('''pick_and_place_node.cpp'''), the global '''application''' object provides access to the program variables through its '''cfg''' member. For instance, in order to use the "WORLD_FRAME_ID" global variable we would do the following:

ROS_INFO_STREAM("world frame: " << application.cfg.WORLD_FRAME_ID)

Node Initialization¶

In the '''pick_and_place_node.cpp''' file, the following block of code in the "main" function initializes the '''!PickAndPlace''' application class and its main ros and MoveIt! components.

int main(int argc,char** argv)
{
  geometry_msgs::Pose box_pose;
  std::vector<geometry_msgs::Pose> pick_poses, place_poses;

  /* =========================================================================================*/
  /*    INITIALIZING ROS NODE
      Goal:
      - Observe all steps needed to properly initialize a ros node.
      - Look into the 'cfg' member of PickAndPlace to take notice of the parameters that
        are available for the rest of the program. */
  /* =========================================================================================*/

  // ros initialization
  ros::init(argc,argv,"pick_and_place_node");
  ros::NodeHandle nh;
  ros::AsyncSpinner spinner(2);
  spinner.start();

  // creating pick and place application instance
  PickAndPlace application;

  // reading parameters
  if(application.cfg.init())
  {
    ROS_INFO_STREAM("Parameters successfully read");
  }
  else
  {
    ROS_ERROR_STREAM("Parameters not found");
    return 0;
  }

  // marker publisher
  application.marker_publisher = nh.advertise<visualization_msgs::Marker>(
          application.cfg.MARKER_TOPIC,1);

  // planning scene publisher
  application.planning_scene_publisher = nh.advertise<moveit_msgs::PlanningScene>(
        application.cfg.PLANNING_SCENE_TOPIC,1);

  // MoveIt! interface
  application.move_group_ptr = MoveGroupPtr(
          new move_group_interface::MoveGroup(application.cfg.ARM_GROUP_NAME));

  // motion plan client
  application.motion_plan_client = nh.serviceClient<moveit_msgs::GetMotionPlan>(application.cfg.MOTION_PLAN_SERVICE);

  // transform listener
  application.transform_listener_ptr = TransformListenerPtr(new tf::TransformListener());

  // marker publisher (rviz visualization)
  application.marker_publisher = nh.advertise<visualization_msgs::Marker>(
          application.cfg.MARKER_TOPIC,1);

  // target recognition client (perception)
  application.target_recognition_client = nh.serviceClient<collision_avoidance_pick_and_place::GetTargetPose>(
          application.cfg.TARGET_RECOGNITION_SERVICE);

  // grasp action client (vacuum gripper)
  application.grasp_action_client_ptr = GraspActionClientPtr(
          new GraspActionClient(application.cfg.GRASP_ACTION_NAME,true));

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