未使用消息过滤器 C++ 调用 ROS2 回调答案

【问题标题】：ROS2 Callback not being called using Message Filters C++未使用消息过滤器 C++ 调用 ROS2 回调
【发布时间】：2023-01-05 16:51:46
【问题描述】：

我在尝试在我的代码中实现消息过滤器时遇到了一些问题。使用这个简单的例子，一切都会编译，但在运行时不会调用回调函数。有谁知道为什么会这样？我已经检查了两个主题的 QoS，它们匹配，所以我不知道为什么没有调用回调函数。我在 Ubuntu 20.04 上运行 ROS2 Galactic。任何帮助将不胜感激！

#include "rclcpp/rclcpp.hpp"
#include "sensor_msgs/msg/image.hpp"
#include "sensor_msgs/msg/point_cloud2.hpp"
#include <message_filters/subscriber.h>
#include <message_filters/time_synchronizer.h>
#include <message_filters/sync_policies/approximate_time.h>

//using std::placeholders::_1;

class MinimalSubscriber : public rclcpp::Node
{
public:

message_filters::Subscriber<sensor_msgs::msg::Image> image_sub_;
message_filters::Subscriber<sensor_msgs::msg::PointCloud2> cloud_sub_;

MinimalSubscriber()
: Node("minimal_subscriber_left")
{
  
  image_sub_.subscribe(this, "/left/image_raw");
  cloud_sub_.subscribe(this, "/model/prius_hybrid/laserscan/points");
  
  typedef message_filters::sync_policies::ApproximateTime<sensor_msgs::msg::Image, sensor_msgs::msg::PointCloud2> approximate_policy;
  message_filters::Synchronizer<approximate_policy>syncApproximate(approximate_policy(10), image_sub_, cloud_sub_);
  syncApproximate.registerCallback(&MinimalSubscriber::topic_callback, this); 
  
};

public:
    void topic_callback(const sensor_msgs::msg::Image::SharedPtr image, const 
    sensor_msgs::msg::PointCloud2::SharedPtr cloud2)
    { 
      std::cout<<"Hello messages are being received";
      RCLCPP_INFO(this->get_logger(), "Publishing");    
    }; 
};

int main(int argc, char * argv[])
{
  rclcpp::init(argc, argv);
  rclcpp::spin(std::make_shared<MinimalSubscriber>());
  rclcpp::shutdown();
  return 0;
}

【问题讨论】：

标签： ros2

【解决方案1】：

原因是您的 syncApproximate 变量的范围在构造函数中是局部的，并且在构造函数退出时超出范围。您需要将syncApproximate 声明为类MinimalSubscriber 的成员变量。例子：

class MinimalSubscriber : public rclcpp::Node
{
public:

message_filters::Subscriber<sensor_msgs::msg::Image> image_sub_;
message_filters::Subscriber<sensor_msgs::msg::PointCloud2> cloud_sub_;
typedef message_filters::sync_policies::ApproximateTime<sensor_msgs::msg::Image, sensor_msgs::msg::PointCloud2> approximate_policy;
message_filters::Synchronizer<approximate_policy>syncApproximate;

MinimalSubscriber()
: Node("minimal_subscriber_left")
{
  
  image_sub_.subscribe(this, "/left/image_raw");
  cloud_sub_.subscribe(this, "/model/prius_hybrid/laserscan/points");
  syncApproximate(approximate_policy(10), image_sub_, cloud_sub_);
  syncApproximate.registercallback(&MinimalSubscriber::topic_callback, this);
}

public:
    void topic_callback(const sensor_msgs::msg::Image::SharedPtr image, const 
    sensor_msgs::msg::PointCloud2::SharedPtr cloud2)
    { 
      std::cout<<"Hello messages are being received";
      RCLCPP_INFO(this->get_logger(), "Publishing");    
    }; 
};

int main(int argc, char * argv[])
{
  rclcpp::init(argc, argv);
  rclcpp::spin(std::make_shared<MinimalSubscriber>());
  rclcpp::shutdown();
  return 0;
}

【讨论】：