High network usage for remote mapping and RTABMap blank

[hrishi-v]

Hi there, I was wondering if you had any advice on how we could reduce the network usage for the following two launch files? I followed your tutorial on remote mapping, but I'm still seeing a usage of around 1.5 Megabytes/s. Another issue that we face, which we are not sure if it's related to the network usage, is that RTABMap takes around 30 seconds to a minute to start displaying the odometry and point cloud, until then it's just a black screen, and says no data received in the terminal. However, after a random amount of time, it starts working.

The Raspberry Pi's launch file:

<launch>
  <arg name="rate"  default="10"/>
  <include file="$(find freenect_launch)/launch/freenect.launch">
     <arg name="depth_registration" value="True" />
  </include>

  <group ns="camera">
    <node pkg="nodelet" type="nodelet" name="rgbd_sync" args="load rtabmap_sync/rgbd_sync camera_nodelet_manager" output="screen">
      <param name="compressed_rate"  type="double" value="$(arg rate)"/>
      <param name="approx_sync"      type="bool"   value="true"/>
      <param name="approx_sync_max_interval" type="double" value="0.025"/>
      <remap from="rgb/image"       to="rgb/image_rect_color"/>
      <remap from="depth/image"     to="depth_registered/image_raw"/>
      <remap from="rgb/camera_info" to="rgb/camera_info"/>
      <remap from="rgbd_image"      to="rgbd_image"/>
    </node>
  </group>      
</launch>

The client that does the mapping's launch file:

<launch>
    <arg name="rtabmap_args" default="--delete_db_on_start"/>

    <arg name="subscribe_rgbd" default="true"/>
    <arg name="rgbd_topic" default="/camera/rgbd_image"/>
    <arg name="compressed" default="true"/>

    <include file="$(find rtabmap_launch)/launch/rtabmap.launch">
        <arg name="subscribe_rgbd" value="$(arg subscribe_rgbd)"/>
        <arg name="rgbd_topic" value="$(arg rgbd_topic)"/>
        <arg name="compressed" value="$(arg compressed)"/>
        <arg name="rtabmap_args" value="$(arg rtabmap_args)"/>
    </include>
</launch>

Both are roslaunched without any extra parameters. Thank you for your time.

[matlabbe]

1.5 MB/s at 10 Hz image data is not too bad. Based on freenect example here, it was ~900 KB/s for 5Hz using rgbd_sync.

For the 30 sec lack of data, you may doublecheck if the rgbd_image topic relayed on host computer is published at a constant 10Hz:

rostopic hz /camera/rgbd_image_relay

You may check system monitor like in those examples to see if the bandwidth usage is constant or there are some drop when you see rtabmap not updating.