gazebo_ros_control_plugin.cpp

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/* Author: Dave Coleman, Jonathan Bohren
   Desc:   Gazebo plugin for ros_control that allows 'hardware_interfaces' to be plugged in
   using pluginlib
*/

// Boost
#include <boost/bind.hpp>

#include <gazebo_ros_control/gazebo_ros_control_plugin.h>
#include <urdf/model.h>

namespace gazebo_ros_control
{

GazeboRosControlPlugin::~GazeboRosControlPlugin()
{
  // Disconnect from gazebo events
  gazebo::event::Events::DisconnectWorldUpdateBegin(update_connection_);
}

// Overloaded Gazebo entry point
void GazeboRosControlPlugin::Load(gazebo::physics::ModelPtr parent, sdf::ElementPtr sdf)
{
  ROS_INFO_STREAM_NAMED("gazebo_ros_control","Loading gazebo_ros_control plugin");


  // Save pointers to the model
  parent_model_ = parent;
  sdf_ = sdf;

  // Error message if the model couldn't be found
  if (!parent_model_)
  {
    ROS_ERROR_STREAM_NAMED("loadThread","parent model is NULL");
    return;
  }

  // Check that ROS has been initialized
  if(!ros::isInitialized())
  {
    ROS_FATAL_STREAM_NAMED("gazebo_ros_control","A ROS node for Gazebo has not been initialized, unable to load plugin. "
      << "Load the Gazebo system plugin 'libgazebo_ros_api_plugin.so' in the gazebo_ros package)");
    return;
  }

  // Get namespace for nodehandle
  if(sdf_->HasElement("robotNamespace"))
  {
    robot_namespace_ = sdf_->GetElement("robotNamespace")->Get<std::string>();
  }
  else
  {
    robot_namespace_ = parent_model_->GetName(); // default
  }

  // Get robot_description ROS param name
  if (sdf_->HasElement("robotParam"))
  {
    robot_description_ = sdf_->GetElement("robotParam")->Get<std::string>();
  }
  else
  {
    robot_description_ = "robot_description"; // default
  }

  // Get the robot simulation interface type
  if(sdf_->HasElement("robotSimType"))
  {
    robot_hw_sim_type_str_ = sdf_->Get<std::string>("robotSimType");
  }
  else
  {
    robot_hw_sim_type_str_ = "gazebo_ros_control/DefaultRobotHWSim";
    ROS_DEBUG_STREAM_NAMED("loadThread","Using default plugin for RobotHWSim (none specified in URDF/SDF)\""<<robot_hw_sim_type_str_<<"\"");
  }

  // Get the Gazebo simulation period
  ros::Duration gazebo_period(parent_model_->GetWorld()->GetPhysicsEngine()->GetMaxStepSize());

  // Decide the plugin control period
  if(sdf_->HasElement("controlPeriod"))
  {
    control_period_ = ros::Duration(sdf_->Get<double>("controlPeriod"));

    // Check the period against the simulation period
    if( control_period_ < gazebo_period )
    {
      ROS_ERROR_STREAM_NAMED("gazebo_ros_control","Desired controller update period ("<<control_period_
        <<" s) is faster than the gazebo simulation period ("<<gazebo_period<<" s).");
    }
    else if( control_period_ > gazebo_period )
    {
      ROS_WARN_STREAM_NAMED("gazebo_ros_control","Desired controller update period ("<<control_period_
        <<" s) is slower than the gazebo simulation period ("<<gazebo_period<<" s).");
    }
  }
  else
  {
    control_period_ = gazebo_period;
    ROS_DEBUG_STREAM_NAMED("gazebo_ros_control","Control period not found in URDF/SDF, defaulting to Gazebo period of "
      << control_period_);
  }


  // Get parameters/settings for controllers from ROS param server
  model_nh_ = ros::NodeHandle(robot_namespace_);
  ROS_INFO_NAMED("gazebo_ros_control", "Starting gazebo_ros_control plugin in namespace: %s", robot_namespace_.c_str());

  // Read urdf from ros parameter server then
  // setup actuators and mechanism control node.
  // This call will block if ROS is not properly initialized.
  const std::string urdf_string = getURDF(robot_description_);
  if (!parseTransmissionsFromURDF(urdf_string))
  {
    ROS_ERROR_NAMED("gazebo_ros_control", "Error parsing URDF in gazebo_ros_control plugin, plugin not active.\n");
    return;
  }

  // Load the RobotHWSim abstraction to interface the controllers with the gazebo model
  try
  {
    robot_hw_sim_loader_.reset
      (new pluginlib::ClassLoader<gazebo_ros_control::RobotHWSim>
        ("gazebo_ros_control",
          "gazebo_ros_control::RobotHWSim"));

    robot_hw_sim_ = robot_hw_sim_loader_->createInstance(robot_hw_sim_type_str_);
    urdf::Model urdf_model;
    const urdf::Model *const urdf_model_ptr = urdf_model.initString(urdf_string) ? &urdf_model : NULL;

    if(!robot_hw_sim_->initSim(robot_namespace_, model_nh_, parent_model_, urdf_model_ptr, transmissions_))
    {
      ROS_FATAL_NAMED("gazebo_ros_control","Could not initialize robot simulation interface");
      return;
    }

    // Create the controller manager
    ROS_DEBUG_STREAM_NAMED("ros_control_plugin","Loading controller_manager");
    controller_manager_.reset
      (new controller_manager::ControllerManager(robot_hw_sim_.get(), model_nh_));

    // Listen to the update event. This event is broadcast every simulation iteration.
    update_connection_ =
      gazebo::event::Events::ConnectWorldUpdateBegin
      (boost::bind(&GazeboRosControlPlugin::Update, this));

  }
  catch(pluginlib::LibraryLoadException &ex)
  {
    ROS_FATAL_STREAM_NAMED("gazebo_ros_control","Failed to create robot simulation interface loader: "<<ex.what());
  }

  ROS_INFO_NAMED("gazebo_ros_control", "Loaded gazebo_ros_control.");
}

// Called by the world update start event
void GazeboRosControlPlugin::Update()
{
  // Get the simulation time and period
  gazebo::common::Time gz_time_now = parent_model_->GetWorld()->GetSimTime();
  ros::Time sim_time_ros(gz_time_now.sec, gz_time_now.nsec);
  ros::Duration sim_period = sim_time_ros - last_update_sim_time_ros_;

  // Check if we should update the controllers
  if(sim_period >= control_period_) {
    // Store this simulation time
    last_update_sim_time_ros_ = sim_time_ros;

    // Update the robot simulation with the state of the gazebo model
    robot_hw_sim_->readSim(sim_time_ros, sim_period);

    // Compute the controller commands
    controller_manager_->update(sim_time_ros, sim_period);
  }

  // Update the gazebo model with the result of the controller
  // computation
  robot_hw_sim_->writeSim(sim_time_ros, sim_time_ros - last_write_sim_time_ros_);
  last_write_sim_time_ros_ = sim_time_ros;
}

// Called on world reset
void GazeboRosControlPlugin::Reset()
{
  // Reset timing variables to not pass negative update periods to controllers on world reset
  last_update_sim_time_ros_ = ros::Time();
  last_write_sim_time_ros_ = ros::Time();
}

// Get the URDF XML from the parameter server
std::string GazeboRosControlPlugin::getURDF(std::string param_name) const
{
  std::string urdf_string;

  // search and wait for robot_description on param server
  while (urdf_string.empty())
  {
    std::string search_param_name;
    if (model_nh_.searchParam(param_name, search_param_name))
    {
      ROS_INFO_ONCE_NAMED("gazebo_ros_control", "gazebo_ros_control plugin is waiting for model"
        " URDF in parameter [%s] on the ROS param server.", search_param_name.c_str());

      model_nh_.getParam(search_param_name, urdf_string);
    }
    else
    {
      ROS_INFO_ONCE_NAMED("gazebo_ros_control", "gazebo_ros_control plugin is waiting for model"
        " URDF in parameter [%s] on the ROS param server.", robot_description_.c_str());

      model_nh_.getParam(param_name, urdf_string);
    }

    usleep(100000);
  }
  ROS_DEBUG_STREAM_NAMED("gazebo_ros_control", "Recieved urdf from param server, parsing...");

  return urdf_string;
}

// Get Transmissions from the URDF
bool GazeboRosControlPlugin::parseTransmissionsFromURDF(const std::string& urdf_string)
{
  transmission_interface::TransmissionParser::parse(urdf_string, transmissions_);
  return true;
}


// Register this plugin with the simulator
GZ_REGISTER_MODEL_PLUGIN(GazeboRosControlPlugin);
} // namespace