Emergency braking

src/robot/emergency_braking/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.8)
+project(emergency_braking)
+
+if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
+  add_compile_options(-Wall -Wextra -Wpedantic)
+endif()
+
+# find dependencies
+find_package(ament_cmake REQUIRED)
+# uncomment the following section in order to fill in
+# further dependencies manually.
+# find_package(<dependency> REQUIRED)
+find_package(rclcpp REQUIRED)
+find_package(std_msgs REQUIRED)
+find_package(nav_msgs REQUIRED)
+find_package(visualization_msgs REQUIRED)
+find_package(sensor_msgs REQUIRED)
+find_package(ackermann_msgs REQUIRED)
+
+find_package(tf2_ros REQUIRED)
+find_package(tf2_geometry_msgs REQUIRED)
+
+if(BUILD_TESTING)
+  find_package(ament_lint_auto REQUIRED)
+  # the following line skips the linter which checks for copyrights
+  # comment the line when a copyright and license is added to all source files
+  set(ament_cmake_copyright_FOUND TRUE)
+  # the following line skips cpplint (only works in a git repo)
+  # comment the line when this package is in a git repo and when
+  # a copyright and license is added to all source files
+  set(ament_cmake_cpplint_FOUND TRUE)
+  ament_lint_auto_find_test_dependencies()
+endif()
+
+add_executable(emergency_braking_node src/emergency_braking.cpp)
+target_include_directories(emergency_braking_node PUBLIC include)
+
+
+
+ament_target_dependencies(emergency_braking_node rclcpp std_msgs nav_msgs visualization_msgs sensor_msgs ackermann_msgs tf2_ros tf2_geometry_msgs)
+
+
+# Install the meshes folder
+#install(DIRECTORY assets/
+#  DESTINATION share/${PROJECT_NAME}/assets
+#)
+
+install(TARGETS
+  emergency_braking_node
+
+  DESTINATION lib/${PROJECT_NAME}
+)
+
+
+ament_package()

src/robot/emergency_braking/package.xml

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+<?xml version="1.0"?>
+<?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
+<package format="3">
+  <name>emergency_braking</name>
+  <version>0.0.0</version>
+  <description>TODO: Package description</description>
+  <maintainer email="140906428+erinjhu@users.noreply.github.com">bolty</maintainer>
+  <license>TODO: License declaration</license>
+
+  <buildtool_depend>ament_cmake</buildtool_depend>
+
+  <test_depend>ament_lint_auto</test_depend>
+  <test_depend>ament_lint_common</test_depend>
+
+  <export>
+    <build_type>ament_cmake</build_type>
+  </export>
+</package>

src/robot/emergency_braking/src/emergency_braking.cpp

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+#include <cmath>
+
+#include "ackermann_msgs/msg/ackermann_drive_stamped.hpp"
+#include "nav_msgs/msg/odometry.hpp"
+#include "rclcpp/rclcpp.hpp"
+#include "sensor_msgs/msg/laser_scan.hpp"
+
+using std::placeholders::_1;
+
+class EmergencyBraking : public rclcpp::Node {
+
+   public:
+        EmergencyBraking() : Node("emergency_braking_node") {
+            brake_pub_ = this->create_publisher<ackermann_msgs::msg::AckermannDriveStamped>("drive", 10);
+            scan_sub_ = this->create_subscription<sensor_msgs::msg::LaserScan>("scan", 10, std::bind(&EmergencyBraking::scan_callback, this, _1));
+            odom_sub_ = this->create_subscription<nav_msgs::msg::Odometry>("ego_racecar/odom", 10, std::bind(&EmergencyBraking::odom_callback, this, _1));
+        }
+
+   private:
+        double speed = 0.0;
+
+        rclcpp::Publisher<ackermann_msgs::msg::AckermannDriveStamped>::SharedPtr brake_pub_;
+        rclcpp::Subscription<sensor_msgs::msg::LaserScan>::SharedPtr scan_sub_;
+        rclcpp::Subscription<nav_msgs::msg::Odometry>::SharedPtr odom_sub_;
+
+        void odom_callback(const nav_msgs::msg::Odometry::ConstSharedPtr msg) {
+            this->speed = msg->twist.twist.linear.x;
+        }
+
+        void scan_callback(const sensor_msgs::msg::LaserScan::ConstSharedPtr scan_msg) {
+            // calculate TTC
+            bool brake = false;
+            double threshold = 1;
+            for (std::size_t i = 0; i < scan_msg->ranges.size(); i++) {
+                double range = scan_msg->ranges[i];
+                bool not_valid = std::isnan(range) || range > scan_msg->range_max || range < scan_msg->range_min;
+                if (not_valid) {
+                    continue;
+                }   
+                double component = this->speed * std::cos(scan_msg->angle_min + (double)i * scan_msg->angle_increment);
+                // ensure speed is not 0 (don't divide by 0)
+                double v = std::max(component, 0.001);
+                double ttc = range / v;
+                RCLCPP_INFO(this->get_logger(), "ttc: %f", ttc);
+                if (ttc < threshold) {
+                    brake = true;
+                    break;
+                }
+            }
+            // publish braking message by setting speed to 0
+            if (brake) {
+                auto brake_msg = ackermann_msgs::msg::AckermannDriveStamped();
+                brake_msg.drive.speed = 0.0;
+                RCLCPP_INFO(this->get_logger(), "stop car");  
+                this->brake_pub_->publish(brake_msg);
+            }
+        }
+};
+
+int main(int argc, char** argv) {
+    rclcpp::init(argc, argv);
+    rclcpp::spin(std::make_shared<EmergencyBraking>());
+    rclcpp::shutdown();
+    return 0;
+}