Starting procrob_functional with a launchfile

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Hello there, i'm trying to launch the procrob_funtional face recognition tool via launchfile. By starting the Fserver via rosrun you have to go to the directory in which the "facedata.xml" etc. are stored. How can I realize that in a launchfile? I'm using ros groovy and the following code:

<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="mjpeg" />
    <param name="camera_frame_id" value="usb_cam" />
    <param name="io_method" value="mmap"/>
  </node>
  <node name="Fserver" pkg="face_recognition" type="Fserver" output="screen"> 
    <param name="haarcascade_frontalface_alt" value="$(find face_recognition)/haarcascade_frontalface_alt.xml"/>
    <param name="facedata" value="$(find face_recognition)/facedata.xml"/>
    <param name="train" value="$(find face_recognition)/train.txt"/>
  </node>
  <node name="Fclient" pkg="face_recognition" type="Fclient" output="screen">
  </node>
</launch>

Thanks for your help!