waitForTransform

 while (nh.ok())
  {
    try
    {
        //ROS_INFO("Attempting to read pose...");
        ros::Time now=ros::Time::now();
    listener.waitForTransform("/map","/base_link",now,ros::Duration(1.0));
        ROS_INFO("Got a transform! x = %f, y = %f",transform.getOrigin().x(),transform.getOrigin().y());
    }
    catch (tf::TransformException ex)
    {
        ROS_ERROR("Nope! %s", ex.what());
    }


    //rate.sleep();

  }