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I have a problem about how to sucscribe the topic only once,In some time, I only hope to get the first data from the topic, rather than change the publisher. So how should I do? This is my code:

#include  <ros/ros.h>
#include <sensor_msgs/NavSatFix.h>
#include <geometry_msgs/PointStamped.h>
static geometry_msgs::PointStamped point;

void imageCallback(const sensor_msgs::NavSatFix::ConstPtr &msg)
{
  point.point.x=msg->latitude;
  point.point.y=msg->longitude;
  point.point.z=msg->altitude;
}



int main(int argc, char **argv)
{
  ros::init(argc, argv, "test");
  ros::NodeHandle nh;
  ros::Subscriber positions_sub = nh.subscribe("/POSITIONS", 3, &imageCallback);
  ros::spin();
}

In this code, I can get many points, but I only hope to get the first point. What should I change in tthe code ? THANKS!

symbol lookup error Sorry to bother you. When I use this code using :rosrun feature_extraction feature_extraction_node,

Sorry, I can not get the solution. Can you give me an example? My hope is to loop the imageCallback only once. Thanks!

How to subscirbe the topic only once I have a problem about how to sucscribe the topic only once,In some time, I only ho

How to subscirbe the topic only once I have a problem about how to sucscribe the topic only once,In some time, I only ho

How to subscirbe the topic only once I have a problem about how to sucscribe the topic only once,In some time, I only ho

How to subscribe many topic in one code and save data in one txt file I hope to subscribe many topics in one code, and I

How to subscribe many topic in one code and save data in one txt file I hope to subscribe many topics in one code, and I

I want to achieve receiving and transform data using rostopic at the same time or in a low time. I know that ros::subscriber can subscribe rostopic and receive the data included in topic. So I hope to process the data in one topic and send the processing-data to another topic, and others can subscribe the new topic. Such as the code:

void receiveGPS(const sensor_msgs::NavSatFix::ConstPtr &msg)
{

  gps_common::GPSFix gps;

  gps.header.stamp=msg->header.stamp;

  gps.status.status=msg->status.status;

  gps.latitude=msg->latitude;

  gps.longitude=msg->longitude;

  gps.altitude=msg->altitude;

  gps.position_covariance[0]=msg->position_covariance[0];
  gps.position_covariance[4]=msg->position_covariance[4];
  gps.position_covariance[8]=msg->position_covariance[8];
}

int main(int argc, char **argv)
{

// Set up ROS.

  ros::init(argc, argv, "receiveGPS");

  ros::NodeHandle n;

  ros::Subscriber sub = n.subscribe("gps", 2,&receiveGPS);

  ros::spin();

}

I can get gps.latitude from the topic "gps",and I hope to send gps.latitude to another topic and publish it. Could you tell me what should I do next? Thanks!

OK! You are right, I will try it soon. This is my first time using Q&A, this is a good start for me! Thank you!

I hope to subscribe the topic and deal with the data in it firstly, and the send the processed data to another topic tha

The question about rostopic ros::publish ros::subscribe I want to achieve receiving and transform data using rostopic a

The question about ros::publisher and ros::subscriber I want to achieve receiving and transform data using rostopic at