I need to filter my point cloud and I found this link: https://answers.ros.org/question/10121/point-cloud-box-filtering/

I have created a launch file commented the x y nodelets. I want to filter the ground. I have a tof camera and I dont want to see the ground when I drive around. So my problem is when I start the camera and then the launch file for the point cloud I get this warning: "This node/nodelet subscribes topics only when subscribed." What does this mean? what do I have to change? In the z node, I have a remap from ~input to <my camera point cloud>

Thank you in advance

---

Edit: launch file:

<node pkg="nodelet" type="nodelet" name="pcl_manager" args="manager" output="screen" />

  <!-- Run a VoxelGrid filter to clean NaNs and downsample the data -->
  <node pkg="nodelet" type="nodelet" name="voxel_grid" args="load pcl/VoxelGrid pcl_manager" output="screen">
    <remap from="~input" to="/royale_camera_driver/point_cloud" />
    <rosparam>
      filter_field_name: z
      filter_limit_min: 0.01
      filter_limit_max: 1.5
      filter_limit_negative: False
      leaf_size: 0.01
    </rosparam>
  </node>

I have put this in the launch file. But I always get the warning that I didn't subscribe. But I already do the remapping

   virtual void warnNeverSubscribedCallback(const ros::WallTimerEvent& event)
   {
     if (!ever_subscribed_)
     {
       NODELET_WARN("This node/nodelet subscribes topics only when subscribed.");
     }
  }