Added demo ROS2

Author: Javier Moreno

external_node/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.5)
+project(external_node)
+
+# Default to C++14
+if(NOT CMAKE_CXX_STANDARD)
+  set(CMAKE_CXX_STANDARD 14)
+endif()
+
+if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
+  add_compile_options(-Wall -Wextra -Wpedantic)
+endif()
+
+find_package(ament_cmake REQUIRED)
+find_package(rclcpp REQUIRED)
+find_package(std_msgs REQUIRED)
+
+add_executable(external_node main.cpp)
+ament_target_dependencies(external_node rclcpp std_msgs)
+
+install(TARGETS
+  external_node
+  DESTINATION lib/${PROJECT_NAME}
+)
+
+ament_package()

external_node/COLCON_IGNORE

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+# Minimal publisher examples
+
+This package contains a few different strategies for creating short nodes which blast out messages.
+The `talker_timer_lambda` and `talker_timer_member_function` recipes create subclasses of `rclcpp::Node` and set up an `rclcpp::timer` to periodically call functions which publish messages.
+The `talker_without_subclass` recipe instead instantiates a `rclcpp::Node` object *without* subclassing it, which works, but is not compatible with composition, and thus is no longer the recommended style for ROS 2 coding.

external_node/README.md

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+// Copyright 2016 Open Source Robotics Foundation, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "rclcpp/rclcpp.hpp"
+#include "std_msgs/msg/float64.hpp"
+#include "std_msgs/msg/string.hpp"
+using std::placeholders::_1;
+
+class ExternalNode : public rclcpp::Node
+{
+public:
+  ExternalNode() : Node("external_node")
+  {
+    power_publisher_ = this->create_publisher<std_msgs::msg::Float64>("engine_power");
+    
+    altitude_subscription_ = this->create_subscription<std_msgs::msg::String>("status_report", std::bind(&ExternalNode::topic_callback, this, _1));
+  }
+
+private:
+  rclcpp::Publisher<std_msgs::msg::Float64>::SharedPtr power_publisher_;
+  rclcpp::Subscription<std_msgs::msg::String>::SharedPtr altitude_subscription_;
+
+  void topic_callback(const std_msgs::msg::String::SharedPtr msg)
+  {
+    if (strcmp(msg->data.c_str(), "Failure!!") == 0)
+        {
+          //std_msgs__msg__Float64 message;
+          auto message = std_msgs::msg::Float64();
+          message.data = 10;
+          this->power_publisher_->publish(message);
+        }
+        else if (strcmp(msg->data.c_str(), "Failure!!") == 0)
+        {
+          auto message = std_msgs::msg::Float64();
+          message.data = 5;
+          this->power_publisher_->publish(message);
+        }
+        else
+        {
+          RCLCPP_INFO(this->get_logger(), "Unkwnow status: '%s'", msg->data.c_str())
+        }  
+  }
+};
+
+int main(int argc, char * argv[])
+{
+  rclcpp::init(argc, argv);
+  rclcpp::spin(std::make_shared<ExternalNode>());
+  rclcpp::shutdown();
+  return 0;
+}

external_node/main.cpp

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+<?xml version="1.0"?>
+<?xml-model href="http://download.ros.org/schema/package_format2.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
+<package format="2">
+  <name>external_node</name>
+  <version>0.0.1</version>
+  <description>Demo. Node running on ros2</description>
+  <maintainer email="javiermoreno@eprosima.com">Javier Moreno</maintainer>
+  <license>Apache License 2.0</license>
+  <author>Javier Moreno</author>
+
+  <buildtool_depend>ament_cmake</buildtool_depend>
+
+  <build_depend>rclcpp</build_depend>
+  <build_depend>std_msgs</build_depend>
+
+  <exec_depend>rclcpp</exec_depend>
+  <exec_depend>std_msgs</exec_depend>
+
+  <export>
+    <build_type>ament_cmake</build_type>
+  </export>
+</package>
+