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    "# Custom ROS Message for Line Params\n",
    "All of the following instructions are based on [this](http://wiki.ros.org/ROS/Tutorials/CreatingMsgAndSrv#Creating_a_msg) guide.\n",
    "\n",
    "First create the message file using the following commands:\n",
    "```\n",
    "cd ~/bwsi-uav/catkin_ws/src/aero_control\n",
    "mkdir msg\n",
    "touch msg/Line.msg\n",
    "gedit msg/Line.msg\n",
    "```\n",
    "\n",
    "In the message file, add:\n",
    "```\n",
    "float64 x\n",
    "float64 y\n",
    "float64 vx\n",
    "float64 vy\n",
    "```\n",
    "This will enable us to transmit a `P = <x, y> + t * <vx, vy>` line parameterization. (`t` can be any real number and `P` is a point on the line)\n",
    "\n",
    "Each line has the sub-message type followed by the name of the variable.\n",
    "\n",
    "## Building the message with catkin\n",
    "We need to make sure that the msg files are turned into source code for C++, Python, and other languages:\n",
    "\n",
    "Open `aero_control/package.xml`, and make sure these two lines are in it and uncommented:\n",
    "```\n",
    "<build_depend>message_generation</build_depend>\n",
    "<exec_depend>message_runtime</exec_depend>\n",
    "```\n",
    "\n",
    "Open `aero_control/CMakeLists.txt` in your favorite text editor (rosed from the previous tutorial is a good option).\n",
    "\n",
    "Add the message_generation dependency to the find_package call which already exists in your CMakeLists.txt so that you can generate messages. You can do this by simply adding message_generation to the list of COMPONENTS such that it looks like this:\n",
    "```\n",
    "# Do not just add this to your CMakeLists.txt, modify the existing text to add message_generation before the closing parenthesis\n",
    "find_package(catkin REQUIRED COMPONENTS\n",
    "   roscpp\n",
    "   rospy\n",
    "   std_msgs\n",
    "   message_generation\n",
    ")\n",
    "```\n",
    "\n",
    "Also make sure you export the message runtime dependency.\n",
    "```\n",
    "catkin_package(\n",
    "  ...\n",
    "  CATKIN_DEPENDS message_runtime ...\n",
    "  ...)\n",
    "```\n",
    "\n",
    "Find the following block of code:\n",
    "```\n",
    "# add_message_files(\n",
    "#   FILES\n",
    "#   Message1.msg\n",
    "#   Message2.msg\n",
    "# )\n",
    "```\n",
    "\n",
    "Uncomment it by removing the # symbols and then replace the stand in Message*.msg files with your .msg file, such that it looks like this:\n",
    "```\n",
    "add_message_files(\n",
    "  FILES\n",
    "  Line.msg\n",
    ")\n",
    "```\n",
    "\n",
    "Now we must ensure the generate_messages() function is called.\n",
    "\n",
    "For ROS Hydro and later, you need to uncomment these lines:\n",
    "\n",
    "```\n",
    "# generate_messages(\n",
    "#   DEPENDENCIES\n",
    "#   std_msgs\n",
    "# )\n",
    "```\n",
    "\n",
    "so it looks like:\n",
    "```\n",
    "generate_messages(\n",
    "  DEPENDENCIES\n",
    "  std_msgs\n",
    ")\n",
    "```\n",
    "\n",
    "\n",
    "\n",
    "At the end, run:\n",
    "```\n",
    "cd ~/bwsi-uav/catkin_ws/\n",
    "catkin_make\n",
    "source devel/setup.bash\n",
    "```\n",
    "\n",
    "To verify that the message was built sucessfully, run\n",
    "```\n",
    "rosmsg show aero_control/Line\n",
    "```"
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    "## Modifying `talker.py` and `listener.py` to use custom messages\n",
    "Fill out the `TODO` sections in `line_tracker/src/talker.py` and `line_tracker/src/listener.py`.\n",
    "\n",
    "You will probabally find the following guide/example code helpful: [link](http://wiki.ros.org/ROS/Tutorials/CustomMessagePublisherSubscriber%28python%29)\n",
    "\n",
    "Dont worry about making any files exicutable since we will be using launchfiles\n",
    "\n",
    "To run these two files together, use `roslaunch launch/talk_listen.launch` in the `line_tracker` package"
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Writing `detector.py`\n",
    "Fill out the TODO sections in `line_tracker/src/detector.py`, you should be able to reuse code from `line_tracker/src/talker.py`, your line paramaterization notebook, and [this](downward_cam_bag.html?highlight=recording#Integrating-opencv-and-ROS-images) example code.\n",
    "\n",
    "To run your code, use `roslaunch aero_control detect_listen.launch` in the `aero_control` package\n"
   ]
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