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Orocos/ROS Services tutorial

This tutorial will teach how to set up an Orocos component to expose its Operations as ROS services.

Note

If you don't have a working version of Orocos + ROS installed in your system, please refer to the first tutorial :doc:`Installation <tutorial_ros1_1_installation>`.

These tutorials assume you have a working knowledge of Orocos components, if not read :ref:`orocos-component-builders-manual` or follow the basic :doc:`RTT tutorials <../rtt/tutorials>`.

In this tutorial we will show you how to expose the operations of your Orocos component as ROS services.

In general the signature of the operation you want to expose as a ROS service will have to adhere to the typical ROS service callback:

bool operation(Service::Request&, Service::Response&);

Note

If you want to use custom ROS services, see :ref:`custom-rtt-messages`.

Take for example the following component:

Header file:

#ifndef STANDARDCOMPONENT_H
#define STANDARDCOMPONENT_H

#include <rtt/RTT.hpp>
#include <rtt/Component.hpp>
#include <my_msgs/MyService.h>

class StandardComponent:
    public RTT::TaskContext
{
public:
    /// Constructor
    StandardComponent(std::string const& name);

    /// Destructor
    ~StandardComponent(){}

    bool myOperation(my_msgs::MyService::Request& request, my_msgs::MyService::Response& response)
    {
        response.success = false;
        if (request.data)
        {
            response.success = true;
        }

        return true;
    }

    /// Configure
    bool configureHook();

    /// Update
    void updateHook();
};

#endif // StandardComponent_H

And cpp file:

#include <orocos-ros-services/StandardComponent.h>

StandardComponent::StandardComponent(std::string const& name)
    : RTT::TaskContext(name)
{
    this->provides("simple_service")->addOperation("myOperation", &StandardComponent::myOperation, this, RTT::ClientThread);
}

bool StandardComponent::configureHook()
{
    return true;
}

void StandardComponent::updateHook()
{

    RTT::log(RTT::Info) << "Waking up!" << RTT::endlog();

}

ORO_CREATE_COMPONENT(StandardComponent)

That exposes an operation using the MyService type from the my_msgs package.

We can deploy with the following script:

import("orocos-ros-services")
import("rtt_rosnode")
import("rtt_roscomm")
import("rtt_std_srvs")
import("rtt_my_msgs")

loadComponent("my_component", "StandardComponent")

// load the rosservice service in the component
loadService("my_component", "rosservice")

// connect the operation to the ros service:
my_component.rosservice.connect("simple_service.myOperation", "/my_namespace/my_operation", "my_msgs/MyService")

Operations can also be exposed as ROS services without having to adher to the typical bool operation(Service::Request& request, Service::Response& response) interface, with the use of wrappers. For the services in std_srvs the following operation signatures are supported:

std_srvs/Empty:
- bool empty()                     // The service call fails if empty() returns false!
                                // Use std_srvs/Trigger if the result should be returned as the response.
- void empty()

std_srvs/SetBool:
- bool setBool(bool, std::string &message_out)
- bool setBool(bool)               // response.message will be empty
- std::string setBool(bool)        // response.success = true
- void setBool(bool)               // response.success = true and response.message will be empty

std_srvs/Trigger:
- bool trigger(std::string &message_out)
- bool trigger()                   // response.message will be empty
- std::string trigger()            // response.success = true

This can be extended to other ros service types, see the header files in the rtt_std_srvs package.