Re: [ros-users] tf to get robot position

Tully,

Thanks for the info, now is working, I was using ros::Time::now() because the tf tutorial says this is better.

Nicolas

From: tfoote@willowgarage.com
Date: Tue, 11 Jan 2011 11:44:10 -0800
To: ros-users@code.ros.org
Subject: Re: [ros-users] tf to get robot position

Hi Nicolas,

If you print out the exception string we can help you more. I suspect that it might show you that your query is too early instead of too late.

If you are not particular about exactly when the transform is looked up I would suggest that you use ros::Time(0), this is a special value which will lookup to the latest available time. Instead of ros::Time::now() which forces a value.



Tully

2011/1/11 Nicolás Alvarez Picco <nicolasapicco@hotmail.com>







Hi!

I am using this code to get the position of my robo:

pose2d_t ROS_Link::get_robot_pose(){
pose2d_t ret;



tf::StampedTransform transform;
geometry_msgs::TransformStamped msg;



std::string source_frame("/base_link");//!!este y el de abajo van!!!
std::string target_frame("/map"); //!! Ver q va bien aca!

  try{
     ros::Time now = ros::Time::now();

     tl->waitForTransform(target_frame, source_frame, now, ros::Duration(1.0));

     tl->lookupTransform(target_frame, source_frame, ros::Time::now(), transform);
  } 
  catch(...){

    ROS_ERROR("Error obtaining robot pose");
    return ret;
  }

tf::transformStampedTFToMsg(transform, msg);

ret.x = msg.transform.translation.x;


ret.y = msg.transform.translation.y;
ret.yaw = tf::getYaw(msg.transform.rotation);//!! WHY??



return ret;
}

the robot is a a model from videre erratic simulated in gazebo. I am attaching the tf tree with the frecuencies. But every time I run my program I have the ROS_ERROR("Error obtaining robot pose"); and the time to time I get the position.


So as I can see it is a problem of the speed of the transfomation. What can I do I have tried with more time in the wait for transform line?

Thanks

Nicolas

                      

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--
Tully Foote
Systems Engineer
Willow Garage, Inc.
tfoote@willowgarage.com
(650) 475-2827

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