Adding a 3D vision sensor to Gazebo

In Gazebo, we can simulate the robot movement and its physics;  we can also simulate sensors too.

To build a sensor in Gazebo, we must model the behavior of that sensor in Gazebo. There are some prebuilt sensor models in Gazebo that can be used directly in our code without writing a new model.

Here, we are adding a 3D vision sensor (commonly known as an rgb-d sensor) called the Asus Xtion Pro model in Gazebo. The sensor model is already implemented in the gazebo_ros_pkgs/gazebo_plugins ROS package, which we have already installed in our ROS system.

Each model in Gazebo is implemented as a Gazebo-ROS plugin, which can be loaded by inserting it into the URDF file.

Here is how we include a Gazebo definition and a physical robot model of Xtion Pro in the seven_dof_arm_with_rgbd.xacro robot xacro file:

<xacro:include filename="$(find mastering_ros_robot_description_pkg)/urdf/sensors/xtion_pro_live.urdf.xacro"/>  

Inside xtion_pro_live.urdf.xacro, we can see the following lines:

<?xml version="1.0"?> 
<robot xmlns:xacro="http://ros.org/wiki/xacro"> 
  <xacro:include filename="$(find mastering_ros_robot_description_pkg)/urdf/sensors/xtion_pro_live.gazebo.xacro"/> 
................... 
  <xacro:macro name="xtion_pro_live" params="name parent *origin *optical_origin">  
................... 
    <link name="${name}_link"> 
       ...................... 
  <visual> 
        <origin xyz="0 0 0" rpy="0 0 0"/> 
        <geometry> 
          <mesh filename="package://mastering_ros_robot_description_pkg/meshes/sensors/xtion_pro_live/xtion_pro_live.dae"/> 
        </geometry> 
        <material name="DarkGrey"/> 
    </visual> 
    </link>  
 
</robot> 

Here, we can see it includes another file called xtion_pro_live.gazebo.xacro, which consists of the complete Gazebo definition of Xtion Pro.

We can also see a macro definition named xtion_pro_live, which contains the complete model definition of Xtion Pro, including links and joints:

<mesh filename="package://mastering_ros_robot_description_pkg/meshes/sensors/xtion_pro_live/xtion_pro_live.dae"/> 

In the macro definition, we are importing a mesh file of the Asus Xtion Pro, which will be shown as the camera link in Gazebo.

In the  mastering_ros_robot_description_pkg/urdf/sensors/xtion_pro_live.gazebo.xacro file, we can set the Gazebo-ROS plugin of Xtion Pro. Here, we will define the plugin as macro with RGB and depth camera support. Here is the plugin definition:

          <plugin name="${name}_frame_controller"     filename="libgazebo_ros_openni_kinect.so"> 
          <alwaysOn>true</alwaysOn> 
          <updateRate>6.0</updateRate> 
          <cameraName>${name}</cameraName> 
          <imageTopicName>rgb/image_raw</imageTopicName> 
 
        </plugin>  

The plugin filename of Xtion Pro is libgazebo_ros_openni_kinect.so, and we can define the plugin parameters, such as the camera name, image topics, and so on.