3. Navigation

3.1. Hokuyo laser scanner

We will add a laser scanner to the mobile robot. The sensor behavior is already defined in gazebo as a plugin. The plugin that we will use is called libgazebo_ros_laser.so. We will create a new xacro file called hokuyo_laser.xacro, we define a link, a joint and add the gazebo plugin:

<gazebo reference="hokuyo_link">
<material>Gazebo/Blue</material>
<turnGravityOff>false</turnGravityOff>
<sensor type="ray" name="head_hokuyo_sensor">
  <pose>${length/2} 0 0 0 0 0</pose>
  <visualize>false</visualize>
  <update_rate>40</update_rate>
  <ray>
    <scan>
      <horizontal>
        <samples>720</samples>
        <resolution>1</resolution>
        <min_angle>-1.570796</min_angle>
        <max_angle>1.570796</max_angle>
      </horizontal>
    </scan>
    <range>
      <min>0.10</min>
      <max>10.0</max>
      <resolution>0.001</resolution>
    </range>
  </ray>
  <plugin name="gazebo_ros_head_hokuyo_controller" filename="libgazebo_ros_laser.so">
    <topicName>/scan</topicName>
    <frameName>hokuyo_link</frameName>
  </plugin>
</sensor>
</gazebo>

Create a new xacro file called mobile_robot_with_laser.xacro, where we include the mobile robot definition and the laser macro:

<?xml version="1.0"?>
<robot name="mobile_robot"
  xmlns:xacro="http://www.ros.org/wiki/xacro">

  <!-- ================================================================================================================= -->
  <!-- INCLUDE FILES -->
  <xacro:include filename="$(find mobile_car_description)/urdf/mobile_robot.xacro" />
  <xacro:include filename="$(find mobile_car_description)/urdf/laser/hokuyo_laser.xacro" />

  <!-- ================================================================================================================= -->
   <!-- laser -->
  <hokuyo_laser name="hokuyo_link" parent="body_link" length="${hokuyo_length}" width="${hokuyo_width}" height="${hokuyo_height}" x="${hokuyo_x}" y="${hokuyo_y}" z="${hokuyo_z}" mass="${hokuyo_mass}"/>

  <!-- ================================================================================================================= -->

</robot>

Open the robot in gazebo:

roslaunch mobile_car_gazebo mobile_car_gazebo.launch model:='$(find mobile_car_description)/urdf/mobile_robot_with_laser.xacro'

Using rostopic list we can see the topic called /scan is being published. rostopic echo /scan to see the laser scanner value.

3.2. Add camera

<gazebo reference="camera_link">
    <sensor type="camera" name="camera1">
      <update_rate>30.0</update_rate>
      <camera name="head">
        <horizontal_fov>1.3962634</horizontal_fov>
        <image>
          <width>800</width>
          <height>800</height>
          <format>R8G8B8</format>
        </image>
        <clip>
          <near>0.02</near>
          <far>300</far>
        </clip>
        <noise>
          <type>gaussian</type>
          <!-- Noise is sampled independently per pixel on each frame.
               That pixel's noise value is added to each of its color
               channels, which at that point lie in the range [0,1]. -->
          <mean>0.0</mean>
          <stddev>0.007</stddev>
        </noise>
      </camera>
      <plugin name="camera_controller" filename="libgazebo_ros_camera.so">
        <alwaysOn>true</alwaysOn>
        <updateRate>0.0</updateRate>
        <cameraName>robot/camera1</cameraName>
        <imageTopicName>image_raw</imageTopicName>
        <cameraInfoTopicName>camera_info</cameraInfoTopicName>
        <frameName>camera_link</frameName>
        <hackBaseline>0.07</hackBaseline>
        <distortionK1>0.0</distortionK1>
        <distortionK2>0.0</distortionK2>
        <distortionK3>0.0</distortionK3>
        <distortionT1>0.0</distortionT1>
        <distortionT2>0.0</distortionT2>
      </plugin>
    </sensor>
  </gazebo>

Show image:

rosrun image_view image_view image:=/robot/camera1/image_raw

3.3. Loading maps in gazebo

3.4. Teleoperate the robot