Week-2 progress

DUMMY Libraries

Second week commenced with discussion over creating an interface for tools to support both ROS1 and ROS2. There were many challenges which were discussed with mentors over the meeting. For achieving this task I was suggested to use conditional compilation and building for both distros in a single code. To start with it, this week I was supposed to create a dummy library.

First it is important to understand what is it and how it works?

We wish to develop the tool which can work when both distros are present, one of them is present or even none is present. Dependencies of ROS should not result in errors. After reading the required config from a configuration file the interface decides internally to shake hands with selected distro (i.e. set up the environment to include necessary header files and compile that ROS code).

link-tool

Conditional Compilation with pre-processor directives

First part involved learning about pre-processor directives in C++ and define them in CMakeLists.txt

Our concern is with conditional compilation directives which are

idfef ( if defined )
ifndef (if not defined) For better clarity these are the links studied for understanding link1, link2

Dummy example with ROS1 and ROS2

Getting right path to get rid of sourcing environment.

Discussion in issues:

Source the ROS and ROS2 environment for different cases from the cpp file (Intended interface) Issue#01
Conditional compilation failing Issue#02

Now, moving to the solution:

For ROS1

—Solved for ROS1 by Adding these lines in CMakeLists.txt
```
  SET(CMAKE_PREFIX_PATH "${CMAKE_PREFIX_PATH} /home/pankhuri/ros2_ws/install";/opt/ros/melodic)
```
Challenge: Since our files are in /opt/ros/melodic path or in/install for workspace I was using these two paths individually. But using them together with help of dilimiter ‘;’ solved the issue.

Helpful links: answers.ros #01
For ROS2

–AMENT PACKAGE- ‘ament_package is a Python module. Python uses the PYTHONPATH variable. It doesn’t retrieve the CMAKE_PREFIX_PATH, so setting it will not extend the Python search path’. First we need to set the right path.

—Solved for ROS2 by adding these lines in CMakeLists.txt
```
  SET(ENV{PYTHONPATH} "/opt/ros/dashing/lib/python3.6/site-packages/")
  SET(CMAKE_PREFIX_PATH "${CMAKE_REFIX_PATH} home/pankhuri/ros2_ws/install;/opt/ros/dashing")
    
```
Challenge: I tried it in a way simialar to ROS1 but there was an error of ‘No module named ament package’. Resolving it consumed a lot of time.

Helpful links studied for this:

answers.ros.org

ament/ament_tools

How to properly set AMENT_PREFIX_PATH?

ImportError: ‘from ament_package

Testing the tool

Initially cases were tasted for ROS1 and ROS2 path individually with different CMake file and after successful runs they were integrated into one using –cmake-args and if()..else()..endif() conditions in CMakeLists.txt

Most of the work in this week was to correct the CMakeLists.txt for both ROS and ROS2 and get it right. So, here is the final version of it:

  cmake_minimum_required(VERSION 3.5)
project(dummyexample)


 # Default to C++14
if(NOT CMAKE_CXX_STANDARD)
  set(CMAKE_CXX_STANDARD 14)
endif()

if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
  add_compile_options(-Wall -Wextra -Wpedantic -Wunused-parameter)
endif()

SET(rosversion "1" CACHE STRING "Some user-specified option") 
   
if(rosversion) 
    message("THIS IS ROS1")

    SET(CMAKE_PREFIX_PATH "${CMAKE_PREFIX_PATH} /home/pankhuri/catkin_ws/install;/opt/ros/melodic")

    find_package(roscpp REQUIRED)
    find_package(std_msgs REQUIRED)
    if(roscpp_FOUND) 
      message("ROS1 found")
      add_definitions(-DROS1_H) 
      SET(ROS1_H ON) 
    ELSE()
      message("ROS1 not found")
      SET(ROS1_H OFF) 
    endif()

    include_directories(${roscpp_INCLUDE_DIRS})
    #include_directories(${std_msgs_INCLUDE_DIRS})

    add_executable(main main.cpp)
    target_link_libraries(main ${roscpp_LIBRARIES} ${std_msgs_LIBRARIES} )

    install(TARGETS main
            DESTINATION bin)

else()
    message("THIS IS ROS2")

    SET(ENV{PYTHONPATH} "/opt/ros/dashing/lib/python3.6/site-packages/")
    SET(CMAKE_PREFIX_PATH "${CMAKE_PREFIX_PATH} home/pankhuri/ros2_ws/install;/opt/ros/dashing")

    find_package(ament_cmake REQUIRED)
    find_package(rclcpp REQUIRED)
    find_package(sensor_msgs REQUIRED)

    if(rclcpp_FOUND) 
      message("ROS2 found")
      add_definitions(-DROS2_H) 
      SET(ROS2_H ON) 
    ELSE()
      message("ROS2 not found")
      SET(ROS2_H OFF) 
    endif()
 
    include_directories(
    include
      ${rclcpp_INCLUDE_DIRS}
      ${rmw_connext_cpp_INCLUDE_DIRS}
      ${std_interfaces_INCLUDE_DIRS}
      )

    add_executable(main main.cpp)
    #target_link_libraries(main ${rclcppLIBRARIES} ${std_msgs_LIBRARIES} )
    ament_target_dependencies(main rclcpp std_msgs)
    install(TARGETS main
        DESTINATION bin)

endif()

Hello World Publisher!

This tool works for 4 cases:

Both ROS1 and ROS2 installed
Only ROS1 present
Only ROS2 present
Neither ROS1 nor ROS2 present

(Click on the image to watch video)

Steps to run this example:

Download the dummyexample dummyexample

Cmake version > 3.3 is required. Lower versions will give errors

Build the code:

colcon build --symlink-install \--cmake-args \ -Drosversion:string=0

Note:

-Drosversion:string=1//For ROS1

-Drosversion:string=0//For ROS2

To run it:

Go to build directory where the main file is located (/build/dummyexample/)

./main 1 //For ROS1

./main 2 //For ROS2

Upcoming work:

If possible, use another alternative AMENT_PREEFIX_PATH for setting the path which would be better too since we should utilize ROS2 design features
Attach a subscriber or a listener too
Extend this code for library similar to cameraclient for CamViz tool