Hello. I have a simple tf-tree (sorry, i have not enough point to download picture). May be it is available [here](http://hkar.ru/CjCu).
If no: tf-tree is **map -> odom -> base_link -> lazer**.
When i launch file with gmapping, not always there is an error: >Transform failed during publishing of map_odom transform: Lookup would require extrapolation into the future. Requested time 1436451359.820962500 but the latest data is at time 1436451359.720510500, when looking up transform from frame [base_link] to frame [odom].
It happens not always. But when after this file i launch the other contais **hector_exploration_node**, **hector_exploration_planner** and **hector_costmap**, it happens every time.
I changed the **use_sim_time** parameter: if it is *false*, there is the error, else there isn't error, but the navigation part(second launch file) only starts and doesn't work (freezes).
I did [this](http://wiki.ros.org/navigation/Tutorials/Navigation%20Tuning%20Guide) diagnostic. It works properly.
**Edit:**
> Fist launch file:>>>> name="tf_sender"> >> type="vel_sender.py"> name="vel_sender"> >> command="cat $(find> bot)/car_model.urdf" /> pkg="hokuyo_node" type="hokuyo_node" > name="lidar"> value="/dev/ttyACM1" /> >> type="robot_state_publisher" > name="robot_state_publisher" />>>>> type="hector_mapping" name="gmapping">> >> type="turtle_teleop_key" name="teleop"> /> >
Second:>>>>>> type="exploration_planner_node" > name="hector_exploration_node"> output="screen">> command="load" />> command="load" ns="global_costmap" />> command="load" ns="local_costmap" />> command="load" ns="local_costmap" />> command="load" ns="global_costmap" />> command="load" />> command="load"> ns="/costmap_node/costmap" />>> >> pkg="hector_exploration_controller"> type="simple_exploration_controller"> name="hector_exploration_controller"> output="screen" respawn="true">> to="/turtle1/cmd_vel"/> >> type="hector_costmap"> name="hector_costmap" output="screen"> respawn="false">>>>> value="base_footprint" />>>>>>>>>>>> value="0.3" />>> >>>
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