ar_track_alvar not recognizing an AR tag

edit

I am running a Gazebo simulation with a hector_quadrotor with a front facing camera. I want to use the ar_track_alvar package to recognize a single AR tag in the camera's field of view, and publish the pose information of the AR tag for me to subscribe to in another node. Running rqt_image_view I can see the AR tag in the camera frame, but when I use rostopic echo /ar_pose_marker it keeps outputting a marker with no information, which I think means it is publishing the topic but not finding any markers to include data of. Why isn't it finding the marker and publishing its pose in /ar_pose_marker? I have included my launch file that spawns the quadrotor in the world and initializes the ar_track_alvar package:

<launch> <arg name="paused" default="false"/> <arg name="use_sim_time" default="true"/> <arg name="gui" default="true"/> <arg name="headless" default="false"/> <arg name="debug" default="false"/>

<include file="$(find gazebo_ros)/launch/empty_world.launch"> <arg name="world_name" value="$(find hector_quadrotor_model)/worlds/robot_in_world.world"/> <arg name="paused" value="$(arg paused)"/> <arg name="use_sim_time" value="$(arg use_sim_time)"/> <arg name="gui" value="$(arg gui)"/> <arg name="headless" value="$(arg headless)"/> <arg name="debug" value="$(arg debug)"/> </include>

<include file="$(find hector_quadrotor_gazebo)/launch/spawn_quadrotor_with_cam.launch"/>

<arg name="marker_size" default="4.4"/> <arg name="max_new_marker_error" default="0.08"/> <arg name="max_track_error" default="0.2"/> <arg name="cam_image_topic" default="/front_cam/camera/image"/> <arg name="cam_info_topic" default="/front_cam/camera/camera_info"/> <arg name="output_frame" default="/front_cam_optical_frame"/>

<node name="ar_track_alvar" pkg="ar_track_alvar" type="individualMarkersNoKinect" respawn="false" output="screen" args="_image_transport:=compressed">

  <remap from="camera_image/compressed"  to="$(arg cam_image_topic)/compressed" />
  <remap from="camera_info"   to="$(arg cam_info_topic)" />

</node>

</launch>

I spawn the AR tag with a separate launch file:

<launch>

<arg name="x" default="0.5" />
<arg name="y" default="0.0" />
<arg name="z" default="0.5" />
<arg name="roll" default="0.0"/>
<arg name="pitch" default="1.5708"/>
<arg name="yaw" default="0.0" />

<arg name="urdf_robot_file" default="$(find hector_quadrotor_gazebo)/urdf/ar_0001.urdf" />
<arg name="robot_name" default="ar_0001" />

<include file="$(find hector_quadrotor_gazebo)/launch/spawn_ar0001_urdf.launch">
    <arg name="x" value="$(arg x)" />
    <arg name="y" value="$(arg y)" />
    <arg name="z" value="$(arg z)" />
    <arg name="roll" value="$(arg roll)"/>
    <arg name="pitch" value="$(arg pitch)"/>
    <arg name="yaw" value="$(arg yaw)" />

    <arg name="urdf_robot_file" value="$(arg urdf_robot_file)" />
    <arg name="robot_name" value="$(arg robot_name)" />
</include>

</launch>