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