Custom ROS Message for Line Params

All of the following instructions are based on this guide.

First create the message file using the following commands:

cd ~/bwsi-uav/catkin_ws/src/aero_control
mkdir msg
touch msg/Line.msg
gedit msg/Line.msg

In the message file, add:

float64 x
float64 y
float64 vx
float64 vy

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)

Each line has the sub-message type followed by the name of the variable.

Building the message with catkin

We need to make sure that the msg files are turned into source code for C++, Python, and other languages:

Open aero_control/package.xml, and make sure these two lines are in it and uncommented:

<build_depend>message_generation</build_depend>
<exec_depend>message_runtime</exec_depend>

Open aero_control/CMakeLists.txt in your favorite text editor (rosed from the previous tutorial is a good option).

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:

# Do not just add this to your CMakeLists.txt, modify the existing text to add message_generation before the closing parenthesis
find_package(catkin REQUIRED COMPONENTS
   roscpp
   rospy
   std_msgs
   message_generation
)

Also make sure you export the message runtime dependency.

catkin_package(
  ...
  CATKIN_DEPENDS message_runtime ...
  ...)

Find the following block of code:

# add_message_files(
#   FILES
#   Message1.msg
#   Message2.msg
# )

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:

add_message_files(
  FILES
  Line.msg
)

Now we must ensure the generate_messages() function is called.

For ROS Hydro and later, you need to uncomment these lines:

# generate_messages(
#   DEPENDENCIES
#   std_msgs
# )

so it looks like:

generate_messages(
  DEPENDENCIES
  std_msgs
)

At the end, run:

cd ~/bwsi-uav/catkin_ws/
catkin_make
source devel/setup.bash

To verify that the message was built sucessfully, run

rosmsg show aero_control/Line

Modifying talker.py and listener.py to use custom messages

Fill out the TODO sections in line_tracker/src/talker.py and line_tracker/src/listener.py.

You will probabally find the following guide/example code helpful: link

Dont worry about making any files exicutable since we will be using launchfiles

To run these two files together, use roslaunch launch/talk_listen.launch in the line_tracker package

Writing detector.py

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 example code.

To run your code, use roslaunch aero_control detect_listen.launch in the aero_control package