ETH-Zurich-Exercises

Exercise 1

I first downloaded the zip file given for the exercise 1 from the official website: https://rsl.ethz.ch/education-students/lectures/ros.html
I then extracted the zip file: smb_common into the git folder i made.
I followed this github repository for reference and teleop file. I needed this repo because there were may errors while I ran the launch file of the simulation as I had to install some plugins and the readme files given in the downloaded zip files were not good.
Then I created a workspace ' zurich ' with catkin build.

sudo apt-get install python3-catkin-tools
mkdir -p zurich/src
cd ~/zurich
catkin build

Then I downloaded the required plugins/ dependencies

sudo apt install -y ros-<distro>-hector-gazebo-plugins \
                    ros-<distro>-velodyne \
                    ros-<distro>-velodyne-description \
                    ros-<distro>-velodyne-gazebo-plugins \
                    ros-<distro>-pointcloud-to-laserscan \
                    ros-<distro>-twist-mux

where <distro> can be either melodic or noetic.

catkin build

then I used symlink to link packages in my git folder to my workspace and built the package.

ln -s ~/git/smb_common/smb_gazebo/ ~/zurich/src/
catkin build smb_gazebo

similarly for other 2 packages

Then I created another package ' exer1 ' and built it
Then I made a folder scripts and made a file : 'teleop_twist_keyboard.py' and copied the code from the repo I mentioned. Then, I made it executable using

chmod +x teleop_twist_keyboard.py

Then, I added these lines in the CMake file of the package

catkin_install_python(PROGRAMS scripts/teleop_twist_keyboard.py
  DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION}
)

I launched the simulation with

roslaunch smb_gazebo smb_gazebo.launch

I ran the teleop node with

rosrun exer1 teleop_twist_keyboard.py

errors you may face

when u run the teleop file, you will have to make changes in it based on the name of the package in which u created it.

Now. I changed the world file in launch file code.
I used rqt graph to generate this

Exercise 2

download the zip file and move the package into the same workspace. Make scipts, config, launch folders in the smb_highlevel_controller package
check the topic info /scan, based on that write a node to subscribe to scan topic, its sensor_msgs/LaserScan, so import it accordingly

create a launch file to launch the above subscriber node
then make a config.yaml file with the topic name and queue size in config folder

load the parameter server using the launch file

access the params using rospy.get_param()

check the msg type of laserscan and access the ranges and find min value accordingly
in rviz, using add option add the following with these params in Global Options, Fixed Frame : odom in PointCloud2, Topic: /rslidar_points, Size: 0.05 in LaserScan, Topic: /scan, Size: 0.05 add TF and RobotModel too
save the rviz configuration as default.rviz in a rviz folder inside the package
add the rviz launching command in the launch file
Now you can visualize the point clouds and the laser scan in rviz like this: RVIZ Gazebo
Now you can write a subscriber node which subscribes to the rslidar_points and prints the number of points and can launch it through another launch file