[ros-users] tf to get robot position

[Nicolás Alvarez Picco]

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 at willowgarage.com
Date: Tue, 11 Jan 2011 11:44:10 -0800
To: ros-users at 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 at 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 at willowgarage.com
(650) 475-2827


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