Longitude an latitude values are not updating.

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I'm trying to create a GPS model so that I can later add it to a vehicle simulation. I've looked at the gps test_world file to see how I can add GPS to my model, which is just a cube. I'm getting velocity values but my longitude and latitude values are not changing. Can anyone help?

<sdf version="1.5"> <world name="default">

<!-- Global light source -->
<include>
  <uri>model://sun</uri>
</include>-->

<!-- Ground plane -->
<include>
  <uri>model://ground_plane</uri>
</include>

<spherical_coordinates>
  <surface_model>EARTH_WGS84</surface_model>
  <latitude_deg>0</latitude_deg>
  <longitude_deg>-0</longitude_deg>
  <elevation>0.0</elevation>
  <heading_deg>0</heading_deg>
</spherical_coordinates>

<model name="gps_generic">
  <!-- Give the base link a unique name -->
  <link name="body">
    <pose>0 0 0 0 0 0</pose>
    <inertial>
      <mass>1.2</mass>
      <inertia>
    <ixx>1</ixx>
    <iyy>1</iyy>
    <izz>1</izz>
    <ixy>0</ixy>
    <ixz>0</ixz>
    <iyz>0</iyz>
      </inertia>
    </inertial>
    <!-- Default Position -->

    <collision name="body_collision">
      <geometry>
    <box>
      <size>0.05 0.05 0.05</size>
    </box>
      </geometry>
    </collision>

    <!-- Visuals -->
    <visual name="body_visual">
      <geometry>
    <box>
      <size>0.05 0.05 0.05</size>
    </box>
      </geometry>
    </visual>
      <sensor name="gps" type="gps">
      <pose>0 0 0  0 0 0</pose>
      <update_rate>10.0</update_rate>
      <always_on>true</always_on>
      <gps>
        <position_sensing>
          <horizontal>
        <noise type="gaussian_quantized">
          <mean>0</mean>
          <stddev>1</stddev>
          <bias_mean>3</bias_mean>
          <bias_stddev>1</bias_stddev>
          <precision>0.5</precision>
        </noise>
          </horizontal>
          <vertical>
        <noise type="gaussian_quantized">
          <mean>0</mean>
          <stddev>1</stddev>
          <bias_mean>3</bias_mean>
          <bias_stddev>1</bias_stddev>
          <precision>1.0</precision>
        </noise>
          </vertical>
        </position_sensing>
        <velocity_sensing>
          <horizontal>
        <noise type="gaussian_quantized">
          <mean>0</mean>
          <stddev>0.1</stddev>
          <bias_mean>0.1</bias_mean>
          <bias_stddev>0.1</bias_stddev>
          <precision>0.1</precision>
        </noise>
          </horizontal>
          <vertical>
        <noise type="gaussian_quantized">
          <mean>0</mean>
          <stddev>0.2</stddev>
          <bias_mean>0.2</bias_mean>
          <bias_stddev>0.2</bias_stddev>
          <precision>0.2</precision>
        </noise>
          </vertical>
        </velocity_sensing>
      </gps>
    </sensor>
  </link>
</model>

</world> </sdf>

sensor is this case is a child of link