Could not find a connection between 'map' and 'base_link' with laser.

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Hi all, I have a turtlebot, and add a hokuyo UST 10LX, but now with trouble in mapping . below is the sequence:

1. Add lidar module to robot's urdf file. $ sudo vi urdf/turtlebot_library.urdf.xacro <joint name="laser" type="fixed"> <origin xyz="-0.005 0.00 0.360" rpy="3.14159 0 0"/> <parent link="base_link"/> <child link="base_laser_link"/> </joint> <link name="base_laser_link"> <inertial> <mass value="0.000001"/> <origin xyz="0 0 0"/> <inertia ixx="0.0001" ixy="0.0" ixz="0.0" iyy="0.0001" iyz="0.0" izz="0.0001"/> </inertial> </link>

2. Edit launch to load lidar' driver $ sudo vi /opt/ros/indigo/share/turtlebot_bringup/launch/minimal.launch <node name="hokuyo" pkg="urg_node" type="urg_node"> < !– remap from="scan" to="base_scan" ==This is no longer needed / –> < /node>

3. Then try to map. $ roscore $ roslaunch turtlebot_bringup minimal.launch $ roslaunch turtlebot_navigation gmapping_demo.launch

4. But meet error: Could not find a connection between 'map' and 'base_link' because they are not part of the same tree. Tf has two or more unconnected trees.

5. troubleshooting like this: 5.1 $ rosrun rqt_tf_tree rqt_tf_tree sure, /map is seperated, not belong to any part.

5.2 $ rosrun tf tf_echo map base_link meet the same hints: Could not find a connection between 'map' and 'base_link' ...

5.3 $ rosrun tf tf_echo base_link base_laser_link Exception thrown:"base_laser_link" passed to lookupTransform argument source_frame does not exist.

1. So I am confused. I already add a Lidar module to robot urdf module: base_laser_link is child and base_link is parent. so, since I change the urdf file, I think the ros system will mataintent the tf transform tree automaticly, but how I can not sucessfuly echo the base_link ---> base_laser_link , why this chain failed?

Thank you advanced!!!