Section 1: Installation To add camera functionality to the spiri drone, copy the code below into the sdf file of the model you are using, before the last line.

<!-- joint for camera -->
<joint name="camera_joint" type="fixed">
        
        <parent> spiri::base </parent>
        <child> camera_link::link </child>
</joint>


<!-- link for camera -->
<link name="camera_link">
        <inertial>
                  <pose>0 0 0 0 0 0</pose>
                  <mass>0.01</mass>
                  <inertia>
                    <ixx>2.1733e-06</ixx>
                    <ixy>0</ixy>
                    <ixz>0</ixz>
                    <iyy>2.1733e-06</iyy>
                    <iyz>0</iyz>
                    <izz>1.8e-07</izz>
            </inertia>
    </inertial>  
        <pose>0 0 0.15 0 0 0</pose> 
  <visual name="camera_visual">
    <pose>-0.005 0 0 0 0 0</pose>
    <geometry>
      <box>
        <size>0.01 0.01 0.01</size>
      </box>
    </geometry>
    <material>
      <ambient>0 0 0 1.0</ambient>
      <diffuse>0 0 0 1.0</diffuse>
      <specular>0.0 0.0 0.0 1.0</specular>
      <emissive>0.0 0.0 0.0 1.0</emissive>
    </material>
  </visual>
  <sensor type="multicamera" name="stereo_camera">
      <update_rate>30.0</update_rate>
      <camera name="left">
        <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>
          <mean>0.0</mean>
          <stddev>0.007</stddev>
        </noise>
      </camera>
      <camera name="right">
        <pose>0 -0.07 0 0 0 0</pose>
        <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>
          <mean>0.0</mean>
          <stddev>0.007</stddev>
        </noise>
      </camera>
      <plugin name="stereo_camera_controller" filename="libgazebo_ros_multicamera.so">
        <alwaysOn>true</alwaysOn>
        <updateRate>0.0</updateRate>
        <cameraName>multisense_sl/camera</cameraName>
        <imageTopicName>image_raw</imageTopicName>
        <cameraInfoTopicName>camera_info</cameraInfoTopicName>
        <frameName>left_camera_optical_frame</frameName>
        <!--<rightFrameName>right_camera_optical_frame</rightFrameName>-->
        <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> 
    </link>

Section 2: Modifying the code This section will go through the code section by section and describe what each part represents

Joint: This joint connects the camera link to the main robot. The parent is the main robot (base) and the child is the camera link

<joint name="camera_joint" type="fixed">
        
        <parent> spiri::base </parent>
        <child> camera_link::link </child>
</joint>

Link: This defines the actual camera

<link name="camera_link">

Inertial: This defines the mass and intertial properties. The values are set to be small to not change the model much

    <inertial>
            <pose>0 0 0 0 0 0</pose>
            <mass>0.01</mass>
            <inertia>
                <ixx>2.1733e-06</ixx>
                <ixy>0</ixy>
                <ixz>0</ixz>
                <iyy>2.1733e-06</iyy>
                <iyz>0</iyz>
                <izz>1.8e-07</izz>
            </inertia>
    </inertial>  

Pose: This defines the position where the cameras will be centered

<pose>0 0 0.15 0 0 0</pose>

Visual: this defines the look of the camera

<visual name="camera_visual">
    <pose>-0.005 0 0 0 0 0</pose>
    <geometry>
      <box>
        <size>0.01 0.01 0.01</size>
      </box>
    </geometry>
    <material>
      <ambient>0 0 0 1.0</ambient>
      <diffuse>0 0 0 1.0</diffuse>
      <specular>0.0 0.0 0.0 1.0</specular>
      <emissive>0.0 0.0 0.0 1.0</emissive>
    </material>
  </visual>

Sensor: This defines how and what the camera outputs. The type multicamera corresponds to a stereo camera

<sensor type="multicamera" name="stereo_camera">

Update rate: This parameter defines the frame rate of the cameras

<update_rate>30.0</update_rate>

Next we define the left camera specific parameters

<camera name="left">
        <horizontal_fov>1.5708</horizontal_fov>
        <image>
          <width>1280</width>
          <height>960</height>
          <format>R8G8B8</format>
        </image>
        <clip>
          <near>0.02</near>
          <far>300</far>
        </clip>
        <noise>
          <type>gaussian</type>
          <mean>0.0</mean>
          <stddev>0.007</stddev>
        </noise>
      </camera>

These values still need to be updated to match the camera we are actually using The right camera is similarly defined, along with an offset from the left camera (the pose)

<camera name="right">
        <pose>0 -0.07 0 0 0 0</pose>
        <horizontal_fov>1.5708</horizontal_fov>
        <image>
          <width>1280</width>
          <height>960</height>
          <format>R8G8B8</format>
        </image>
        <clip>
          <near>0.02</near>
          <far>300</far>
        </clip>
        <noise>
          <type>gaussian</type>
          <mean>0.0</mean>
          <stddev>0.007</stddev>
        </noise>
      </camera>

Finally we define some values for ros to use for the topics that we output to, and close everything

<plugin name="stereo_camera_controller" filename="libgazebo_ros_multicamera.so">
        <alwaysOn>true</alwaysOn>
        <updateRate>0.0</updateRate>
        <cameraName>multisense_sl/camera</cameraName>
        <imageTopicName>image_raw</imageTopicName>
        <cameraInfoTopicName>camera_info</cameraInfoTopicName>
        <frameName>left_camera_optical_frame</frameName>
      </plugin>
    </sensor>
    </link>