代码：

<!-- -->
<launch>
  <!--  node name="usb_cam" pkg="usb_cam" type="usb_cam_node" output="screen" >
    <param name="video_device" value="/dev/video0" />
    <param name="image_width" value="640" />
    <param name="image_height" value="480" />
    <param name="pixel_format" value="yuyv" />
    <param name="camera_frame_id" value="usb_cam" />
    <param name="io_method" value="mmap"/>
  </node->
  <node name="image_view" pkg="image_view" type="image_view" respawn="false" output="screen">
    <remap from="image" to="/usb_cam/image_raw"/>
    <param name="autosize" value="true" />
  </node-->
  <node pkg="qr_tf" type="qr_tf" name="qr_tf" args="$(find qr_tf)/param/out_camera_data.xml $(find qr_tf)/param/sampleread.txt" output="screen">
      <remap from="/image_raw" to="/camera/color/image_raw"/>        
  </node>
</launch>