Launch file to start ROS Services? - c++

Question

I created ROS Service with a client and server node. I created a ROS Service that pass the IMU sensors values from the Server to Client. And Im able to call the server and client node and get the values. But when call them with the launch file I got zero
Here the server node
#include "ros/ros.h"
#include <sensor_msgs/Imu.h>
#include "imu_service/ImuValue.h"
ros::ServiceServer service;
double current_x_orientation_s;
double get_imu_orientation_x;
bool get_val(imu_service::ImuValue::Request &req, imu_service::ImuValue::Response &res)
{
ROS_INFO("sending back response");
res.current_x_orientation_s = get_imu_orientation_x;
//.. same for the other IMU values
}
void imuCallback(const sensor_msgs::ImuConstPtr& msg)
{
current_x_orientation_s= msg->orientation.x;
get_imu_orientation_x=current_x_orientation_s;
// ..same for other IMU values
}
int main(int argc, char **argv)
{
ros::init(argc, argv, "imu_status_server");
ros::NodeHandle n;
ros::Subscriber sub = n.subscribe("/thrbot/imu", 10, imuCallback);
service = n.advertiseService("imu_status_server", get_val);
ROS_INFO("Starting server...");
ros::spin();
return 0;
}
Client
#include "ros/ros.h"
#include "ros_services/ImuValue.h"
#include <cstdlib>
ros::ServiceClient client;
int main(int argc, char **argv)
{
ros::init(argc,argv,"imu_client_node");
ros::NodeHandle n;
ros::NodeHandle nh_;
//ros::Subscriber joy_sub_ = nh_.subscribe<sensor_msgs::Joy>("/thrbot/joy", 10, joystick_callback);
client = n.serviceClient<ros_services::ImuValue>("imu_status_server");
ros_services::ImuValue srv;
client.call(srv);
std::cout << "Got accel x: " << srv.response.current_x_orientation_s << std::endl;
return 0;
}
And the launch file
<?xml version="1.0"?>
<launch>
<node name="ImuServerService" pkg="ros_services" type="ImuServerService" output="screen">
</node>
<node name="ImuClientService" pkg="ros_services" type="ImuClientService" output="screen"/>
</launch>
I got 0 as response.
[ INFO] [1631800449.207350420]: Starting server...
[ INFO] [1631800449.212336478]: sending back response
Got accel x: 0
But when manually run the Server and the Client with
rosrun ros_services ImuServerService and rosrun ros_services ImuClientService the value is correct one
Any help?

Answer 1

The reason you're getting 0 back is because the client immediately calls the service on startup. Since it also immediately returns the last cached value and they're both started at almost the same time via roslaunch this means there's essentially no way a message will be received on the topic by the service is called. This works with rosrun because having to manually launch the nodes gives it enough time to actually receive something on the topic. You can observe it by adding a delay to the start of your client like so:
#include "ros/ros.h"
#include "ros_services/ImuValue.h"
#include <cstdlib>
ros::ServiceClient client;
int main(int argc, char **argv)
{
ros::init(argc,argv,"imu_client_node");
ros::NodeHandle n;
ros::NodeHandle nh_;
//ros::Subscriber joy_sub_ = nh_.subscribe<sensor_msgs::Joy>("/thrbot/joy", 10, joystick_callback);
client = n.serviceClient<ros_services::ImuValue>("imu_status_server");
ros_services::ImuValue srv;
ros::Duration(5).sleep(); //Sleep for 5 seconds
client.call(srv);
std::cout << "Got accel x: " << srv.response.current_x_orientation_s << std::endl;
return 0;
}