rtabmap_ros/obstacles_detection

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hi all i created 3d map from environment with rtabmap and stereo camera. for this purpose, stereo images were captured with stereo camera and saved in folder. after this, by using of this launch file the 3d map was created. my question is that, how can i use rtabmap_ros/obstacles_detection nodelet in this launch file to extract obstacles and the ground from a point cloud? please help me

Ubuntu 14.04, Ros indigo