Step 1

• Go to https://rds.theconstructsim.com/
• Create a new project. Choose a informative name and add some description in the description field. (for this tutorial we are using project name poses_to_file)
• Open the project. This will being you to the RDS environment with two menu options Tools and Simulations
• Start an IDE by selecting IDE option from the Tools. IDE is a very useful tool, it lets you navigate and edit files/directories. Try navigating around and verify that the directory layout of the project is as shown below:

    . 
    ├── ai_ws
    ├── catkin_ws
    │   ├── build
    │   ├── devel
    │   └── src
    ├── notebook_ws
    │   ├── default.ipynb
    │   └── images
    └── simulation_ws
        ├── build
        ├── devel
        └── src

Note that we use simulation_ws directory to contain all files related to simulations.
Those files not related to simulations will go to catkin_ws (like python scripts, launch files etc)

Step 2

We will create a new catkin project inside the catkin_ws/src directory

$ cd catkin_ws/src catkin_create_pkg poses_to_file rospy

Next we will create a python script to write the poses to the file. We will create this script inside the newly created project.

$ cd poses_to_file/src touch poses_to_file.py

We have now created a empty script file named poses_to_file.py. We also need to make it executable. Use following commands to make it executable

$ chmod +x poses_to_file.py

Verify the permission by using the listing unix command

$ ls -l

Step 3

We will now write the program inside the python script.

The script contains class named SavePoses with following member functions

• __init__
• sub_callback
• write_to_file

+
The role of __init__ function would be to initialize a Pose type (_pose), a dictionary type (poses_dict) to hold Poses. We will subscribe to the /odom topic as well.

Function sub_callback is the callback for the subscriber we create in the __init__. Inside this callback function we receive the current pose and copy it inside variable _pose.

The function write_to_file is tasked with following:

• initializing dictionary keys pose1, pose2 and pose3
• open a file in write mode
• iterate through the keys of dictionary and write a formatted string containing values corresponding to the keys.

The complete code is as follows:

#! /usr/bin/env python

import rospy
from nav_msgs.msg import Odometry
from geometry_msgs.msg import Pose
import time


class SavePoses(object):
    def __init__(self):
        
        self._pose = Pose()
        self.poses_dict = {"pose1":self._pose, "pose2":self._pose, "pose3":self._pose}
        self._pose_sub = rospy.Subscriber('/odom', Odometry , self.sub_callback)
        self.write_to_file()

    def sub_callback(self, msg):
        
        self._pose = msg.pose.pose
    
    def write_to_file(self):
        
        time.sleep(5)
        self.poses_dict["pose1"] = self._pose
        rospy.loginfo("Written pose1")
        time.sleep(5)
        self.poses_dict["pose2"] = self._pose
        rospy.loginfo("Written pose2")
        time.sleep(5)
        self.poses_dict["pose3"] = self._pose
        rospy.loginfo("Written pose3")
            
        
        with open('poses.txt', 'w') as file:
            
            for key, value in self.poses_dict.iteritems():
                if value:
                    file.write(str(key) + ':\n----------\n' + str(value) + '\n===========\n')
                    
        rospy.loginfo("Written all Poses to poses.txt file")
        


if __name__ == "__main__":
    rospy.init_node('spot_recorder', log_level=rospy.INFO) 
    save_spots_object = SavePoses()
    #rospy.spin() # mantain the service open.