Create ROS

ROS/ROS

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+# RUNNING ROS using virtual machine.
+i am using the virtual machine for ubuntu.
+# EXCERCISE 1 
+- In this we first create the required folder using ---> mkdir ~/git
+- I downloaded the sub_common zip.
+- Then i used :
+manan@manan-virtual-machine:~$ cd ~/git
+manan@manan-virtual-machine:~/git$ unzip smb_common.zip
+- then i made i directory ~/Workspaces/smb_ws/src
+manan@manan-virtual-machine:~/git$ mkdir -p ~/Workspaces/smb_ws/src
+- Using roslaunch to start the simulation and inspect the created nodes and their topics.
+- Source the ROS setup script
+- source /opt/ros/noetic/setup.bash
+-  Launch the simulation
+roslaunch smb_gazebo smb_gazebo.launch
+- In a new terminal, source the ROS setup script again
+-source /opt/ros/noetic/setup.bash
+- List all active nodes 
+rosnode list
+-  List all active topics
+rostopic list
+-  Echo messages from a specific topic (e.g., /cmd_vel)
+-rostopic echo /cmd_vel
+-  Check the publishing rate of a specific topic (e.g., /cmd_vel)
+rostopic hz /cmd_vel
+-    Visualize the ROS computation graph
+-rqt_graph
+- Publish a velocity command to the /cmd_vel topic
+rostopic pub /cmd_vel geometry_msgs/Twist "linear:
+x: 0.5
+y: 0.0
+z: 0.0
+angular:
+x: 0.0
+y: 0.0
+z: 0.5" -r 10
+Navigate to the git folder and clone the repository
+cd ~/git
+git clone https://github.com/ros-teleop/teleop_twist_keyboard.git
+Create a symlink in the catkin workspace
+cd ~/Workspaces/smb_ws/src
+ln -s ~/git/teleop_twist_keyboard .
+-Compile the package
+cd ~/Workspaces/smb_ws
+Catkin_make
+Run teleop_twist_keyboard
+-Source devel/setup.bash
+rosrun teleop_twist_keyboard teleop_twist_keyboard.py
+!-- File: smb_custom_world.launch --
+- launch
+!-- Include the default smb_gazebo.launch file --
+include file="$(find smb_gazebo)/launch/smb_gazebo.launch"
+!-- Override the world_file argument to use a different world --
+arg name="world_file" value="/usr/share/gazebo-11/worlds/robocup14_spl_field.world"/
+/include
+/launch
+- Check if teleop_twist_keyboard is compiled
+roscd teleop_twist_keyboard
+- Source the ROS setup script
+- source /opt/ros/noetic/setup.bash
+- Start the custom launch file
+roslaunch smb_gazebo smb_custom_world.launch

ROS/ROS assignment 2

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+# excercise 2
+- I first downloaded the smb_highlevel_controller zip file from the course website.
+- After that I inspected :
+cd ~/Downloads
+unzip smb_highlevel_controller.zip
+cd smb_highlevel_controller
+cat CMakeLists.txt
+cat package.xml
+- Created a subscriber to the /scan topic :
+nano smb_highlevel_controller_node.cpp
+- then i coded the following :
+#include <ros/ros.h>
+#include <sensor_msgs/LaserScan.h>
+void scanCallback(const sensor_msgs::LaserScan::ConstPtr& msg)
+{
+  ROS_INFO("Received a LaserScan message with %lu ranges", msg->ranges.size());
+}
+
+int main(int argc, char **argv)
+{
+  ros::init(argc, argv, "smb_highlevel_controller_node");
+  ros::NodeHandle nh;
+  ros::Subscriber sub = nh.subscribe("scan", 1000, scanCallback);
+  ros::spin();
+  return 0;
+}
+- Added a parameter file with topic name and queue size for the subscriber of the topic
+/scan:
+nano smb_highlevel_controller_node.cpp
+#include <ros/ros.h>
+#include <sensor_msgs/LaserScan.h>
+
+void scanCallback(const sensor_msgs::LaserScan::ConstPtr& msg)
+{
+  ROS_INFO("Received a LaserScan message with %lu ranges", msg->ranges.size());
+}
+
+int main(int argc, char **argv)
+{
+  ros::init(argc, argv, "smb_highlevel_controller_node");
+  ros::NodeHandle nh;
+
+  ros::Subscriber sub = nh.subscribe("scan", 1000, scanCallback);
+
+  ros::spin();
+
+  return 0;
+}
+- Created a callback method for that subscriber which outputs the smallest distance
+measurement from the vector ranges in the message of the laser scanner to the
+terminal :
+#include <ros/ros.h>
+#include <sensor_msgs/LaserScan.h>
+#include <limits>  // For std::numeric_limits
+
+void scanCallback(const sensor_msgs::LaserScan::ConstPtr& msg)
+{
+  // Initialize minimum range to the maximum possible float value
+  float min_range = std::numeric_limits<float>::infinity();
+
+  // Iterate through the range readings to find the minimum value
+  for (const auto& range : msg->ranges) {
+    if (range < min_range && range >= msg->range_min && range <= msg->range_max) {
+      min_range = range;
+    }
+  }
+
+  // Output the smallest distance measurement to the terminal
+  ROS_INFO("Smallest distance measurement: %f", min_range);
+}
+
+int main(int argc, char **argv)
+{
+  ros::init(argc, argv, "smb_highlevel_controller_node");
+  ros::NodeHandle nh;
+
+  std::string scan_topic;
+  int queue_size;
+
+  nh.getParam("scan_topic", scan_topic);
+  nh.getParam("queue_size", queue_size);
+
+  ros::Subscriber sub = nh.subscribe(scan_topic, queue_size, scanCallback);
+
+  ros::spin();
+
+  return 0;
+}
+- Then i was not able to add the launch file for ex1 , figuring that out...