what is the best way to download code from a .rosinstall file in a groovy catkin workspace?

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I've followed the instructions in this tutorial: http://www.ros.org/wiki/catkin/Tutorials/create_a_workspace to set up my catkin workspace.

Now I would like to download existing code to this workspace:

• I cannot use rosws, as rosws is tied to my rosbuild workspace overlayed on top of the catkin workspace (http://www.ros.org/wiki/catkin/Tutorials/using_rosbuild_with_catkin)
• Is rosinstall the best tool to use? I was trying to catkinize the freenect_stack metapackage, and tried using my existing rosinstall file:

Instructions:

cd ~/catkin_ws/src
rosinstall ./ https://raw.github.com/piyushk/freenect_stack/master/rosinstall/freenect.piyushk.rosinstall --catkin

The following error is generated:

rosinstall operating on /home/piyushk/catkin_ws/src from specifications in rosinstall files  https://raw.github.com/piyushk/freenect_stack/master/rosinstall/freenect.piyushk.rosinstall
(Over-)Writing /home/piyushk/catkin_ws/src/.rosinstall
[freenect_stack] Installing git@github.com:piyushk/freenect_stack.git (version None) to /home/piyushk/catkin_ws/src/freenect_stack
[freenect_stack] Done.
Traceback (most recent call last):
  File "/usr/bin/rosinstall", line 16, in <module>
    sys.exit(not rosinstall_main(sys.argv))
  File "/usr/lib/pymodules/python2.7/rosinstall/rosinstall_cli.py", line 229, in rosinstall_main
    options.catkinpp)
  File "/usr/lib/pymodules/python2.7/rosinstall/rosinstall_cmd.py", line 84, in cmd_generate_ros_files
    setupfiles.generate_catkin_cmake(path, catkinpp)
  File "/usr/lib/pymodules/python2.7/rosinstall/setupfiles.py", line 69, in generate_catkin_cmake
    with open(os.path.join(path, "CMakeLists.txt"), 'w') as cmake_file:
IOError: [Errno 13] Permission denied: '/home/piyushk/catkin_ws/src/CMakeLists.txt'

The error is generated because catkin_make created the CMakeLists.txt in ~/catkin_ws/src/ already. As far as I can tell this error has no effect. Both my rosbuild and catkin workspaces seem to be working properly

Here are my questions:

• Was I supposed to do something else above?
• Can rosws be tied to my catkin workspace if I did not have a rosbuild ws?
• Is there a better way to install code from a .rosinstall file in a catkin workspace?

Thanks!!