The ISSPA Libraries (Python and C++)

Some common tools will be integrated into ISSPA in the form of Python Packages or CPP Libraries, the purpose of which is to interconnect ROS packages and give you a clearer insight into how ISSPA works. In the meantime, you will also understand ISSPA’s program logic and how its components relate to each other.

This tutorial includes the following parts:

ISSPA Python package
- Creating a Python package
- Using a Python package
ISSPA C++ library
- Creating a C++ library
- Using a C++ library

ISSPA Python Packages

First, you need to understand how to create a Python package in ROS and how other ROS packages import it. Second, you will be introduced to the basic usage of Python package with code samples.

Creating a Python Package

Here’s an example of creating a ROS package named isspa, which contains a Python package also named isspa. Create a setup.py file in the root directory of the isspa ROS package, i.e., the directory containing CMakeLists.txt:

mkdir -p ~/ISSPA/src
cd ~/ISSPA/src
catkin_create_pkg isspa rospy roscpp std_msgs
cd isspa
touch setup.py
touch scripts/isspa/__init__.py
touch scripts/isspa/logging_output.py
chmod +x scripts/isspa/logging_output.py

The content of the setup.py file is the following:

from distutils.core import setup
from catkin_pkg.python_setup import generate_distutils_setup

d = generate_distutils_setup(
    packages=['isspa'],
    package_dir={'': 'scripts'},
    version='0.1.0'
)

setup(**d)

Only two lines are important here, the rest are the same every time:

packages=['isspa'],
package_dir={'': 'scripts'},

The first line indicates the name of the package, and the second line indicates the directory where the package is located.

The version should be consistent with the version of the ROS package in the package.xml file.

The content of the logging_output.py file is like the following:

#!/usr/bin/env python
import rospy

def logger(msg):
    rospy.loginfo("Welcome to ISSPA. " + msg)

After that, you also need to change the contents of CMakeLists.txt:

# uncomment these two lines 

catkin_python_setup()

catkin_package()

Finally, you need to build the package:

cd ~/ISSPA
catkin_make
source devel/setup.bash

If all goes well, you can try running the program in another package. A simple test is as follows:

# Open a new terminal and run
roscore
# after having sourced devel/setup.bash

# Open another terminal, and create a script file
cd  ~/ISSPA/src/
catkin_create_pkg test_import_python_package rospy roscpp std_msgs
cd test_import_python_package/scripts
touch test_import_python_package.py
chmod +x test_import_python_package.py

Below we add a simple test_import_python_package.py script under ~/ISSPA/src/test_import_python_package/scripts as an example.

#!/usr/bin/env python
import rospy
from isspa import logging_output

def test_log():
    logging_output.logger("This is a test message.")
    rospy.loginfo("Welcome to ISSPA! This is a message from test_import_python_package.py")

if __name__ == '__main__':
    rospy.init_node('test_import_python_package')
    test_log()

Then, we run the following command to make the script executable:

# In another terminal, after having sourced devel/setup.bash
rosrun test_import_python_package test_import_python_package.py

If everything is working as expected, the following messages will be output:

[INFO] [1632938655.753961]: Welcome to ISSPA. This is a test message.
[INFO] [1632938655.758263]: Welcome to ISSPA! This is a message from test_import_python_package.py

Using a Python Package

Needs to be replenished.

ISSPA C++ Library

The ROS library configuration for C++ is more complex than for Python, so let’s learn how to create it!

Creating a C++ Library

Here’s an example of creating a C++ library named isspa, which also provides a header file named util.h.

mkdir -p ~/ISSPA/src
cd ~/ISSPA/src
catkin_create_pkg isspa rospy roscpp std_msgs
cd isspa
mkdir include
touch include/isspa/util.h

The content of the util.h file is:

#ifndef UTIL_H
#define UTIL_H

#include "ros/ros.h"

namespace isspa
{
    namespace utils {
        void logger(const char* msg);
    }
} // namespace isspa

void sayHello();

#endif // UTIL_H

Don’t misspell #ifndef as #ifdef, otherwise the contents of the header file will not be found during compilation.

Then create util.cpp in the ~/ISSPA/src/isspa/src directory with the following content:

#include "isspa/util.h"
#include <iostream>

using namespace std;

namespace isspa
{
    namespace utils {
        void logger(const char* msg)
        {
            cout << "[Welcome to ISSPA util] " << msg << endl;
        }
    }
} // namespace isspa

void sayHello()
{
    ROS_INFO("Hello from util.cpp");
}

After that, you also need to change the content of CMakeLists.txt within the isspa package:

cmake_minimum_required(VERSION 3.0.2)
project(isspa)

find_package(catkin REQUIRED COMPONENTS
  roscpp
  rospy
  std_msgs
)

catkin_package(
  INCLUDE_DIRS include
  LIBRARIES isspa
  CATKIN_DEPENDS roscpp rospy std_msgs
)

include_directories(
  include
  ${catkin_INCLUDE_DIRS}
)

add_library(${PROJECT_NAME}
  src/util.cpp
)

target_link_libraries(${PROJECT_NAME}
  ${catkin_LIBRARIES}
)

install(TARGETS ${PROJECT_NAME}
  ARCHIVE DESTINATION ${CATKIN_PACKAGE_LIB_DESTINATION}
  LIBRARY DESTINATION ${CATKIN_PACKAGE_LIB_DESTINATION}
  RUNTIME DESTINATION ${CATKIN_GLOBAL_BIN_DESTINATION}
)

install(DIRECTORY include/${PROJECT_NAME}/
  DESTINATION ${CATKIN_PACKAGE_INCLUDE_DESTINATION}
)

At this point, the other package requires changes to CMakeLists.txt and package.xml, assuming the name of the other ROS package is test_import_roscpp_library:

We need to create a main.cpp file first.

cd ~/ISSPA/src/
catkin_create_pkg test_import_roscpp_library rospy roscpp std_msgs
cd test_import_roscpp_library/src
touch src/main.cpp

A simple example is as follows:

// main.cpp
#include <ros/ros.h>
#include <isspa/util.h>

int main(int argc, char** argv)
{
    ros::init(argc, argv, "test_import_roscpp_library");
    ros::NodeHandle nh;

    isspa::utils::logger("Hello from main.cpp");
    sayHello();

    return 0;
}

After that, you also need to change the content of CMakeLists.txt within the test_import_roscpp_library package:

# modify this part

find_package(catkin REQUIRED COMPONENTS
roscpp
rospy
std_msgs
isspa
)

# and these lines

add_executable(test_import_roscpp_library src/main.cpp)
target_link_libraries(test_import_roscpp_library ${catkin_LIBRARIES})
``
and add a ``<depend>isspa</depend>`` tag inside the ``package.xml``.

Finally, you need to build the package:
```bash
cd ~/ISSPA
catkin_make
source devel/setup.bash