How to republish odometry in different frame?

Question

have navigation Odometry, but its some how it is not in the robot body frame. The odometry is being published in world frame, so its not correct. So i need to transform it in the robot body frame as that how should be in the correct way. So I tried to republish the linear velocity in the x axis in the robot body frame, just to check that Im on the correct way, but the code is not working. Here is the ROS node

#include <ros/ros.h>
#include <tf/transform_broadcaster.h>
#include <nav_msgs/Odometry.h>

float linear_x;
ros::Publisher odom_pub;

void poseCallback(const nav_msgs::OdometryConstPtr& msg){

    linear_x = (msg->twist.twist.linear.x );
    nav_msgs::Odometry pose_gt_frame;

        pose_gt_frame.header.frame_id = "world";

    //set the velocity
    pose_gt_frame.child_frame_id = "rexrov2/base_link";
    pose_gt_frame.twist.twist.linear.x = linear_x;

    //publish the message
    odom_pub.publish(pose_gt_frame);

}

int main(int argc, char** argv){
  ros::init(argc, argv, "my_tf_broadcaster");

  ros::NodeHandle node;
  ros::Subscriber sub = node.subscribe("/rexrov2/pose_gt", 10, &poseCallback);
  ros::spin();
  return 0;
};

When run the code I got error

[FATAL] [1635340917.678039503, 15.652000000]: ASSERTION FAILED
    file = /opt/ros/melodic/include/ros/publisher.h
    line = 106
    cond = false
    message = 
[FATAL] [1635340917.680256176, 15.654000000]: Call to publish() on an invalid Publisher
[FATAL] [1635340917.680299807, 15.654000000]:

And also a static frame in the launch file didnt help. What can be wrong? Any help? Thanks

BTables · Answer 1 · 2021-10-27T16:54:31.090

0

You're getting the error because while you declared a publisher variable you have not initialized it yet.

int main(int argc, char** argv){
  ros::init(argc, argv, "my_tf_broadcaster");

  ros::NodeHandle node;
  odom_pub = node.advertise<nav_msgs::Odometry>("some_odom_topic", 5);
  ros::Subscriber sub = node.subscribe("/rexrov2/pose_gt", 10, &poseCallback);
  ros::spin();
  return 0;
};

edited Oct 27 '21 at 16:54

answered Oct 27 '21 at 16:43

BTables

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I change taking into account your suggestions still same problem – Bob9710 Oct 27 '21 at 16:53
@Bob9710 that was my fault. I had a typo in my code. It has been edited now – BTables Oct 27 '21 at 16:54
ok. no error now but its still in the world frame not in the robot body frame. WhY? Whats wrong? – Bob9710 Oct 27 '21 at 17:17
@Bob9710 Because when you create the outgoing message you set `head.frame_id` to `world`. Also changing the `frame_id` field is fairly arbitrary; it's just a string. It doesn't apply any transform, which needs to be done to the actual data. – BTables Oct 27 '21 at 17:24
so head.frame id should be what? so how to apply transform to the actual data? – Bob9710 Oct 27 '21 at 17:32
@Bob9710 `header.frame_id` should be whatever frame the data is in. Again, it's arbitrary though and won't effect the actual data stored in a message. If you want to apply a transform manually you should use [the tf2 package](http://wiki.ros.org/tf2/Tutorials/Writing%20a%20tf2%20listener%20%28C%2B%2B%29) – BTables Oct 27 '21 at 17:34
so I need a tf2 listener? Please can you help with the manually transform? – Bob9710 Oct 27 '21 at 17:43
sorry , Im not clear doe I need tf2 broadcaster to publish the pose to tf2, or a tf2 listener to start using tf2, or both broadcaster and listener?Please, can you clarify this? – Bob9710 Oct 31 '21 at 08:29
@Bob9710 you’ll need a listener. It will listen for transforms to be broadcast. Once broadcast you can use the listener to get the transform and apply it to your data. – BTables Oct 31 '21 at 21:04
should I start a new question regarding the listener? as im not sure if I coded correct or just edit it here in the same question? – Bob9710 Nov 01 '21 at 07:02

How to republish odometry in different frame?

1 Answers1