Could not save point cloud map from rtabmap

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Hi!

I tried to generate a 3D mapping using fetch in gazebo simulation using rtabmap, and I was able to open the rtabmap.db file. Although I could see the map when I open the file with "rtabmap ~/.ros/rtabmap.db," I cannot export as ply. The error is:

Could create clouds for 104 node(s). You may want to activate clouds regeneration option.

When I check the regeneration option in the export console, the error becomes:

Could not create clouds for 188 node(s). The cache may not contain point cloud data. Try re-downloading the map.

The launch file I used for mapping is:

<launch>
  <!-- Kinect cloud to laser scan -->
<node pkg="depthimage_to_laserscan" type="depthimage_to_laserscan" name="depthimage_to_laserscan">
  <remap from="image"       to="/head_camera/depth_registered/image_raw"/>
  <remap from="camera_info" to="/head_camera/depth_registered/camera_info"/>
  <remap from="scan"        to="/base_scan"/>
  <param name="range_max" type="double" value="4"/>
</node>

   <!-- SLAM -->
 <group ns="rtabmap">
<node name="rtabmap" pkg="rtabmap_ros" type="rtabmap" output="screen" args="--delete_db_on_start">
      <param name="frame_id" type="string" value="base_link"/>

      <param name="subscribe_depth" type="bool" value="false"/>
      <param name="subscribe_scan_cloud" type="bool" value="true"/>

      <remap from="odom" to="/odom"/>
      <remap from="scan_cloud" to="/head_camera/depth_registered/points"/>

      <remap from="rgb/image"       to="/head_camera/rgb/image_raw"/>
      <remap from="depth/image"     to="/head_camera/depth_registered/image_raw"/>
      <remap from="rgb/camera_info" to="/head_camera/rgb/camera_info"/>

      <param name="queue_size" type="int" value="10"/>

      <!-- RTAB-Map's parameters -->
      <param name="RGBD/ProximityBySpace"     type="string" value="false"/>
      <param name="RGBD/AngularUpdate"        type="string" value="0.01"/>
      <param name="RGBD/LinearUpdate"         type="string" value="0.01"/>
      <param name="RGBD/OptimizeFromGraphEnd" type="string" value="false"/>
      <param name="Reg/Force3DoF"             type="string" value="true"/>
      <param name="Vis/MinInliers"            type="string" value="12"/>
</node>

<node pkg="rtabmap_ros" type="rtabmapviz" name="rtabmapviz" args="-d $(find rtabmap_ros)/launch/config/rgbd_gui.ini" output="screen">
  <param name="subscribe_depth" type="bool" value="false"/>
  <param name="subscribe_scan_cloud" type="bool" value="true"/>
  <param name="frame_id"           type="string" value="base_link"/>
  <param name="wait_for_transform" type="bool" value="true"/>

  <remap from="odom" to="/odom"/>
  <remap from="scan_cloud" to="/head_camera/depth_registered/points"/>
  <remap from="rgb/image"       to="/head_camera/rgb/image_raw"/>
  <remap from="depth/image"     to="/head_camera/depth_registered/image_raw"/>
  <remap from="rgb/camera_info" to="/head_camera/rgb/camera_info"/>

</node>

</group>
</launch>

Thank you for your help!