frontier_exploration: frontiers inside robot footprint

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Hello,

we started working with the frontier_exploration ros package using gmapping and the navigation-stack on our robot (Volksbot RT6). Both (gmapping and the navigations stack) work fine as long as we use rviz to publish navigation goals. So we began to include the frontier_exploration package. We use the provided launch-file global_map.launch to run the package and only changed the topics and robot specific variables like the footprint and the baselink topic. The thing we don’t understand though is what the lines 15-29 are related to, are those map specific parameters?

When we used rviz to visualize the frontiers topic and we often have frontiers set inside the robots footprint. Since our robot is non-holonomic this often leads to oscillation of the robot and the move_base starts its recovery behaviours. Additional to that we often get the error message 'Could not find nearby clear cell to start search'.

We do have some screenshots of this but since we don’t have the karma points yet we can’t post them. I hope even without those it’s clear what we mean. We’d be glad for any suggestions how to resolve this problem.

Thank you in advance, Miria and Inga

Here is the launch file we use:

<launch>

    <!-- Set to your sensor's range -->
    <arg name="sensor_range" default="1.0"/>

    <node pkg="frontier_exploration" type="explore_client" name="explore_client" output="screen"/>

    <node pkg="frontier_exploration" type="explore_server" name="explore_server" output="screen" >

        <param name="frequency" type="double" value="2.0"/>
        <param name="goal_aliasing" type="double" value="$(arg sensor_range)"/>

        #All standard costmap_2d parameters as in move_base, other than BoundedExploreLayer
        <rosparam ns="explore_costmap" subst_value="true">
            footprint: [[0.36, -0.25], [-0.36, -0.25], [-0.36, 0.25],[0.36, 0.25],[0.51,0.09],[0.51,-0.09]]

            #!transform_tolerance: 0.5
            #update_frequency: 0.5
            #publish_frequency: 0.5

            #must match incoming static map
            global_frame: map
            robot_base_frame: base_footprint
            #resolution: 0.05-->

            rolling_window: true
            track_unknown_space: true

            plugins: 

                - {name: static,           type: "costmap_2d::StaticLayer"}            
                - {name: explore_boundary, type: "frontier_exploration::BoundedExploreLayer"}
                #Can disable sensor layer if gmapping is fast enough to update scans
                - {name: sensor,           type: "costmap_2d::ObstacleLayer"}
                - {name: inflation,        type: "costmap_2d::InflationLayer"}

            static:
                #Can pull data from gmapping, map_server or a non-rolling costmap            
                map_topic: /map
                # map_topic: move_base/global_costmap/costmap   
                subscribe_to_updates: true

            explore_boundary:
                resize_to_boundary: false
                frontier_travel_point: middle
                #set to false for gmapping, true if re-exploring a known area
                explore_clear_space: false

            sensor:
                observation_sources: laser
                laser: {data_type: LaserScan, clearing: true, marking: true, topic: scan_filtered, inf_is_valid: true, raytrace_range: $(arg sensor_range), obstacle_range: $(arg sensor_range)}

            inflation:
                inflation_radius: 0.15
      </rosparam>
    </node>

</launch>

edit:

here's a link to some screenshots we took today with tf visualization overlayed. http://imgur.com/gallery/OrgbB

and here is the gist of our gmapping and move_base configuration https://gist.github.com/anonymous/b0e7aed627ef05d9a233