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Hello! I want to subscribe data from .msg file. However the file has four other msgs inside. The format of the .msg file is:
Header header
geometry_msgs/Vector3 direction
geometry_msgs/Vector3 normal
geometry_msgs/Point palmpos
geometry_msgs/Vector3 ypr
Could you tell me how to read, for example, x,y,z coordinates inside geometry_msgs/Vector3?
I've created a custom msg (msg/mycustom.msg) in my package called mypkg, created a publisher and 2 subscribers, one in python, another in cpp. You can see below:
my_subscriber.py
#!/usr/bin/env python
import rospy
from mypkg.msg import mycustom
def callback(data):
rospy.loginfo("direction x: [" + str(data.direction.x) + "]")
rospy.loginfo("direction y: [" + str(data.direction.y) + "]")
rospy.loginfo("direction z: [" + str(data.direction.z) + "]")
def listener():
rospy.init_node('listener', anonymous=True)
rospy.Subscriber("my_topic", mycustom, callback)
rospy.spin()
if __name__ == '__main__':
listener()
cpp_subscriber.cpp
#include "ros/ros.h"
#include "mypkg/mycustom.h"
void chatterCallback(const mypkg::mycustom::ConstPtr& msg)
{
ROS_INFO("direction x: [%.2f]", msg->direction.x);
ROS_INFO("direction y: [%.2f]", msg->direction.y);
ROS_INFO("direction z: [%.2f]", msg->direction.z);
}
int main(int argc, char **argv)
{
ros::init(argc, argv, "cpp_subscriber");
ros::NodeHandle n;
ros::Subscriber sub = n.subscribe("my_topic", 1000, chatterCallback);
ros::spin();
return 0;
}
There's a video step-by-step showing how I did it: https://www.youtube.com/watch?v=aLfJZf9py0g
If your message is called data then you'd access the x, y, and z components of the direction attribute as:
x = data.direction.x
y = data.direction.y
z = data.direction.z
This is assuming Python. You can access the attributes of messages by using the . operator. If you're using C++, replace the first . with a ->. So it becomes
x = data->direction.x
y = data->direction.y
z = data->direction.z
Actually, "replace the . with a ->" is too generic and not true. It's necessary to do that only to get the pointer of data parameter, then we have to use . for the next attributes (e.g: data->direction.x)
Asked: 2017-11-23 10:01:56 -0500
Seen: 1,242 times
Last updated: Mar 04 '20
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