depthimage_to_laserscan launch

edit

hi, i create a launch file that convert depthimage to laserscan:

<launch>
    <arg name="camera"  default="camera"/>
    <arg name="publish_tf" default="true"/>
    <group if="$(arg scan_processing)">
        <node pkg="nodelet" type="nodelet" name="depthimage_to_laserscan" args="load depthimage_to_laserscan/DepthImageToLaserScanNodelet $(arg camera)/$(arg camera)_nodelet_manager">
        <param name="scan_height" value="10"/>
        <param name="output_frame_id" value="/$(arg camera)_depth_frame"/>
        <param name="range_min" value="0.45"/>
        <remap from="image" to="$(arg camera)/$(arg depth)/image_raw"/>
        <remap from="scan" to="$(arg scan_topic)"/>
    </group>   
</launch>

when i run: roslaunch fake_laser_pkg start_laser.launch, i receive this error:

[start_laser.launch] is neither a launch file in package [fake_laser_pkg] nor is [fake_laser_pkg] a launch file name The traceback for the exception was written to the log file what can i do please?