PR2 self-filtering problem

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Hi, I am a newer using Moveit on PR2 As i am studying on object manipulation recently, the first thing i need to do is to filter PR2 's arm out of the point cloud read by the kinect

I try to solve this problem by creating a sensors_rgbd.yaml into pr2_moveit_generated/config , like this

sensors:
 - sensor_plugin: occupancy_map_monitor/PointCloudOctomapUpdater
   point_cloud_topic: /head_mount_kinect/depth_registered/points
   max_range: 5.0
   padding_offset: 0
   padding_scale: 1.5
   point_subsample: 1
   filtered_cloud_topic: output_cloud

and the result is shown in rviz . However, it seems that PR2 's arm is not filtered well, a majority of the hand is still here

May i ask what should i do in order to get a better filtered point cloud?? thanks a lot!!