RGBDSLAM, Octomap_server and Rviz

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I run the following commands to get a 2D occupancy grid map from the RGBDSLAM node with Kinect.

roscore
roslaunch rgbdslam octomap_server.launch
rosrun rgbdslam rgbdslam
roslaunch openni_launch openni.launch
rosrun rviz rviz

I added a grid and map in rviz as displays. I set the map topic to /projected_map. I generated the PointCloud model and send the model since the model is not sent by default. So I got the occupancy grid map as shown below.

However, I cannot erase the occupancy grid map even by doing two things: first by calling the service of

rosservice call /octomap_server/reset

and then pressing the reset button in rviz at the lower right corner. I even restarted the rviz but it still displayed the map. I wouldn't want always to restart the octomap_server just to reset the map.

How do you reset the map in octomap_server without restarting the node???

Also what does the Online OctoMapping action bar do in RGBDSLAM gui? With or without it, it can still send the model and generate an occupancy grid map successfully. So what is it for??