navigation with known map+rtabmap

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hi i created map with rtabmap and saved. but for navigation the saved map not open. I used rtabmap_ros on a Turtlebot in Gazebo and this is my launch file:

<!-- Turtlebot navigation simulation with RTAB-Map -->
<launch>

  <arg name="database_path"     default="rtabmap.db"/>
  <arg name="localization"      default="true"/>

  <!-- Mapping -->
  <group ns="rtabmap">
    <node name="rtabmap" pkg="rtabmap_ros" type="rtabmap" output="screen">
      <param name="database_path"       type="string" value="$(arg database_path)"/>
      <param name="frame_id"            type="string" value="base_footprint"/>
      <param name="odom_frame_id"       type="string" value="odom"/>
      <param name="subscribe_laserScan" type="bool"   value="true"/>

      <!-- inputs -->
      <remap from="scan"            to="/scan"/>
      <remap from="rgb/image"       to="/camera/rgb/image_raw"/>
      <remap from="depth/image"     to="/camera/depth/image_raw"/>
      <remap from="rgb/camera_info" to="/camera/rgb/camera_info"/>

      <!-- outputs -->
          <remap from="grid_map" to="/map"/> <!-- input for move_base costmap -->

      <!-- RTAB-Map parameters -->
      <param name="RGBD/LocalLoopDetectionSpace" type="string" value="true"/>
      <param name="RGBD/OptimizeSlam2D"          type="string" value="true"/>      
      <param name="Kp/MaxDepth"                  type="string" value="4.0"/>
      <param name="Kp/DetectorStrategy"          type="string" value="6"/> <!-- GFTT/BRIEF -->
      <param name="GFTT/MinDistance"             type="string" value="5"/>
      <param name="LccIcp/Type"                  type="string" value="2"/> <!-- ICP 2D -->
      <param name="LccIcp2/CorrespondenceRatio"  type="string" value="0.1"/> 

      <!-- localization mode -->
      <param     if="$(arg localization)" name="Mem/IncrementalMemory" type="string" value="false"/>
      <param unless="$(arg localization)" name="Mem/IncrementalMemory" type="string" value="true"/>
      <param name="Mem/InitWMWithAllNodes" type="string" value="$(arg localization)"/> 
    </node>
  </group>

  <!-- ******* Navigation - Move Base ******* -->
  <include file="$(find turtlebot_navigation)/launch/includes/move_base.launch.xml"/>


  <!-- ******* Visualization of the Turtlebot on Rviz ******* -->
  <node name="rviz" pkg="rviz" type="rviz" args="-d $(find turtlebot_rviz_launchers)/rviz/navigation.rviz"/>

</launch>

when launched my launch file the massage was: Requesting the map... but map was not loaded