chrono Library - GitMasterNikanjam/C_WiKi GitHub Wiki

The Chrono library, with its capabilities for handling time and timing in C++, can be quite useful in the field of robotics. Robotics often involves precise control, synchronization, and timing of various components and operations. Here are some key applications of the Chrono library in robotics:

  1. Motion Control and Path Planning:
    Robotics involves controlling the motion of robots. You can use the Chrono library to precisely measure and control time intervals for various movements, such as joint movements, wheel rotations, or end-effector positions. This ensures accurate and synchronized motion control.

  2. Sensor Fusion:
    Many robots use multiple sensors, such as cameras, lidars, and accelerometers. The Chrono library can help in synchronizing data from these sensors by providing precise timestamps for sensor readings. This is crucial for sensor fusion, where data from different sensors are combined to create a more accurate perception of the environment.

  3. Real-time Systems:
    In real-time robotics applications, precise timing and synchronization are critical. Chrono provides tools for measuring and controlling time with high precision, making it suitable for real-time control systems that require strict timing constraints.

  4. Simulations and Testing:
    Robotics often involves simulations for testing and development. The Chrono library can be used to control the simulation time and precisely manage the flow of time in simulation environments, which is essential for accurate testing and validation of robot behaviors.

  5. Trajectory Generation:
    For tasks like trajectory planning and control, the Chrono library allows you to represent time intervals, execute motions along a trajectory, and interpolate between key points with high precision. This is valuable for robots performing tasks like pick-and-place operations or path following.

  6. Distributed Systems:
    In multi-robot systems, Chrono can be used to synchronize actions and coordinate tasks among different robots, ensuring that actions are performed at specific times or in a coordinated manner.

  7. Sensor Data Logging and Analysis:
    The Chrono library can be used to timestamp and log sensor data for analysis and debugging. This is helpful in understanding the performance and behavior of robotic systems, especially in complex scenarios.

  8. Time-based Decision Making:
    Robots often make decisions based on time-critical events or schedules. Chrono can be used to implement time-based decision-making algorithms, ensuring that the robot responds to events or changes in the environment at the right time.

  9. Robot Simulation and Control Frameworks:
    Chrono can be integrated into robot simulation and control frameworks to provide a consistent and precise timing mechanism. Frameworks like ROS (Robot Operating System) can benefit from Chrono's time management capabilities.

  10. Monitoring and Logging:
    The Chrono library can be used to timestamp events, actions, and system states in robotics applications. This is crucial for diagnostics, monitoring, and post-mission analysis.

Overall, the Chrono library is a valuable tool for robotics engineers and developers who need to manage and control time in their applications, ensuring accuracy, synchronization, and precise control of robot operations, sensors, and motion. It helps improve the reliability and performance of robotic systems, particularly in applications where precise timing and coordination are essential.

The Chrono library is a C++ library introduced in C++11 and expanded in C++20 for working with date and time. It provides a comprehensive set of classes and functions to handle time-related operations in a type-safe and efficient manner.

chrono provides three main types of clocks: system_clock, steady_clock, and high_resolution_clock. These clocks are used to measure time in various ways.

- system_clock
represents the system-wide real time wall clock. It’s affected by the system’s time adjustments.
- steady_clock
represents a monotonically increasing clock that’s not affected by changes to the system time.
- high_resolution_clock
is the clock with the shortest tick period available on the system.

<chrono> also provides a collection of duration types, including duration<Rep, Period>, that can be used to represent a duration of time. Rep is the representation type (such as int or long) and Period is the ratio of the duration (such as nanoseconds or seconds).
Additionally, <chrono> provides a collection of time point types, including time_point<Clock, Duration>, that can be used to represent a point in time. Clock is the clock type (such as system_clock) and Duration is the duration type (such as seconds).

Chrono library is used to deal with date and time. This library was designed to deal with the fact that timers and clocks might be different on different systems and thus to improve over time in terms of precision. The unique thing about chrono is that it provides a precision-neutral concept by separating duration and point of time (“timepoint”) from specific clocks. chrono is the name of a header and also of a sub-namespace: All the elements in this header (except for the common_type specializations) are not defined directly under the std namespace (like most of the standard library) but under the std::chrono namespace. The elements in this header deal with time. This is done mainly by means of three concepts:

- Duration

A duration object expresses a time span by means of a count like a minute, two hours, or ten milliseconds. For example, “42 seconds” could be represented by a duration consisting of 42 ticks of a 1-second time unit.

// C++ program to illustrate the utility 
// function duration::count
#include <iostream> 
#include <chrono>	 

int main ()
{
	using namespace std::chrono;
	// std::chrono::milliseconds is an 
	// instantiation of std::chrono::duration:- 1 second
	milliseconds mil(1000); 
	
	mil = mil*60;
	
	std::cout << "duration (in periods): ";
	std::cout << mil.count() << " milliseconds.\n";
	
	std::cout << "duration (in seconds): ";
	std::cout << (mil.count() * milliseconds::period::num / 
							milliseconds::period::den);
	std::cout << " seconds.\n";

	return 0;
}

- Output

duration (in periods): 60000 milliseconds.
duration (in seconds): 60 seconds.

- Clock

A clock consists of a starting point (or epoch) and a tick rate. For example, a clock may have an epoch of February 22, 1996 and tick every second. C++ defines three clock types:

system_clock-It is the current time according to the system (regular clock which we see on the toolbar of the computer). It is written as- std::chrono::system_clock
steady_clock-It is a monotonic clock that will never be adjusted.It goes at a uniform rate. It is written as- std::chrono::steady_clock
high_resolution_clock– It provides the smallest possible tick period. It is written as-std::chrono::high_resolution_clock

- Time point

A time_point object expresses a point in time relative to a clock’s epoch. Internally, the object stores an object of a duration type, and uses the Clock type as a reference for its epoch.

// C++ program to illustrate time point
// and system clock functions
#include <iostream>
#include <chrono>
#include <ctime>

// Function to calculate
// Fibonacci series
long fibonacci(unsigned n)
{
	if (n < 2) return n;
	return fibonacci(n-1) + fibonacci(n-2);
}

int main()
{
	// Using time point and system_clock
	std::chrono::time_point<std::chrono::system_clock> start, end;

	start = std::chrono::system_clock::now();
	std::cout << "f(42) = " << fibonacci(42) << '\n';
	end = std::chrono::system_clock::now();

	std::chrono::duration<double> elapsed_seconds = end - start;
	std::time_t end_time = std::chrono::system_clock::to_time_t(end);

	std::cout << "finished computation at " << std::ctime(&end_time)
			<< "elapsed time: " << elapsed_seconds.count() << "s\n";
}

Output:

f(42) = 267914296
finished computation at Wed Jan 4 05:13:48 2017
elapsed time: 2.14538s
It’s important to note that the precision and accuracy of the clocks and durations provided by may vary depending on the system and platform, and it’s always a good idea to check the documentation of your platform for more information.

In C++, the library provides various methods and functionalities for working with durations. Here are some key methods and operations associated with std::chrono::duration :

1- Construction

Durations can be constructed using literals or by explicitly specifying the unit of time. For example:

using namespace std::chrono;

// Construct a duration of 5 seconds
seconds sec(5);

// Construct a duration of 2 milliseconds
milliseconds ms(2);

2- Arithmetic Operations

Durations support basic arithmetic operations, such as addition, subtraction, multiplication, and division:

duration<int> d1 = seconds(5);
duration<int> d2 = milliseconds(200);

// Addition
auto sum = d1 + d2;

// Subtraction
auto difference = d1 - d2;

// Multiplication
auto scaled = d1 * 2;

// Division   
auto divided = d1 / 2;

3- Comparison Operators

Durations can be compared using relational operators (<, >, <=, >=, ==, !=):

duration<int> d1 = seconds(5);
duration<int> d2 = milliseconds(200);

if (d1 > d2) {
    // Do something
}

4- Duration Cast

The std::chrono::duration_cast function can be used to convert durations from one unit to another:

using namespace std::chrono;

// Convert seconds to milliseconds
auto durationInMilliseconds = duration_cast<milliseconds>(seconds(5));

5- Count Accessor

The count() method returns the count of ticks in the duration. For example:

duration<int> d = seconds(5);
int count = d.count();  // Returns 5

6- Zero and Min/Max

The zero() method creates a zero-duration, and min() and max() methods provide the minimum and maximum representable durations, respectively.

using namespace std::chrono;

auto zeroDuration = duration<int>::zero();
auto minDuration = duration<int>::min();
auto maxDuration = duration<int>::max();

These are some of the fundamental methods and operations you can perform with std::chrono::duration in C++. The library provides a flexible and type-safe way to work with time durations, allowing you to perform various time-related calculations.

Duration Literals
C++14 introduced user-defined literals for durations. You can use literals like 1s, 2ms, etc.

using namespace std::chrono_literals;
auto duration = 5s;

Time Point Arithmetic
You can perform arithmetic operations directly on time points.

auto futureTime = currentTime + std::chrono::hours(1);

Time Zone Support
C++20 introduced some facilities for working with time zones, like std::chrono::zoned_time and std::chrono::current_zone() .

Clock Durations
Some clocks have associated durations, which represent the tick period of the clock.

using period = std::chrono::system_clock::period; // period is a std::ratio representing the tick period

Utility Functions
Various utility functions, such as std::chrono::duration_cast for converting between durations, std::chrono::floor for flooring time points, and std::chrono::ceil for ceiling time points.

Remember that the availability of some features might depend on the C++ standard version and the compiler you are using. Always refer to the documentation for the specific version of C++ you are working with.

If you want to ensure that the loop sleeps for the remaining time to achieve a precise interval, you can calculate the remaining time after each iteration and use that value for the std::this_thread::sleep_for. Here's an example:

#include <iostream>
#include <chrono>
#include <thread>

int main() {
    using namespace std::chrono;

    // Set the desired time interval
    milliseconds interval(4);

    // Get the starting time point
    auto startTime = high_resolution_clock::now();

    // Main loop
    while (true) {
        // Your task goes here

        // Get the current time point
        auto currentTime = high_resolution_clock::now();

        // Calculate the elapsed time
        auto elapsedTime = duration_cast<milliseconds>(currentTime - startTime);

        // Check if the desired interval has passed
        if (elapsedTime >= interval) {
            // Your task goes here
            std::cout << "Working every 4 ms" << std::endl;

            // Reset the start time for the next interval
            startTime = currentTime;
        }

        // Calculate the remaining time until the next interval
        auto remainingTime = interval - elapsedTime;

        // Sleep for the remaining time
        std::this_thread::sleep_for(remainingTime);
    }

    return 0;
}

In this modified example:

After the task is executed, the code calculates the remaining time until the next interval by subtracting the elapsed time from the desired interval. The std::this_thread::sleep_for(remainingTime) ensures that the loop sleeps for the remaining time to achieve the precise 4 ms interval.
Keep in mind that the actual execution time of your task inside the loop may still affect the accuracy of achieving the desired interval, and you may need to fine-tune the code based on your application's characteristics.

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