hector_slam sporadic update error of /odom

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Hi

We use a non-holonomic wheeled platform with two SICK s300 laser scanners, and have recently tried to apply hector_slam instead of gmapping because gmapping uses almost 100% cpu and hector_slam uses close to 0%. We run Fuerte and Ubuntu 12.04 LTS. The software is running on one computer on the platform.

However, we have one problem with hector_slam and that is sporadic updates of the odometry.

We have made a launch file with the following

<?xml version="1.0"?>
<launch>
  <node pkg="hector_mapping" type="hector_mapping" name="hector_mapping" output="screen">
        <!-- Frame names -->
        <param name="map_frame" value="/map" />
        <param name="base_frame" value="/base_link" />
        <param name="odom_frame" value"/odom" />
        <param name="scan_topic" value="/scan_unified/scan"/>
  </node>
        <!-- Tf use -->
        <param name="pub_map_odom_transform" value="true"/>
</launch>

When we run the mapping the map updates and builds fine in rviz when moving linearly, but when we start to rotate the robot the scans and map do not align anymore. When looking at the odometry in rviz, it continuously goes between an error and OK. The error we receive is

For frame [odom]: No transform to fixed frame [/map]. TF error: [unable to lookup transform, cache is empty, when looking up transform from frame [/odom] to frame [/map]]

Anyone got an idea to why we receive this sporadic error of the odometry, it shifts between the error and OK every second, sometimes faster, sometimes slower?