Wind velocity to Beaufort conversion algorithms

Table of Contents

• Description
• Velocities conversion to Beaufort per hour
  • Input
  • Moving mean
  • Structures
• Complexities
• Compile & Run
  • Makefile
  • Command line

Description

A toy project which translates wind velocities to Beaufort codes.

A Python program generates wind velocities values in a specific time period and exports them to an output file.

A C++ program parses an input file with timestamp, velocity pairs, finds the average wind velocity for each minute and keeps these minutes' speeds in a fixed size queue in order to calculate a moving mean (MM) wind velocity of the last hour. This MM wind velocity determines the hour's Beaufort code and export this code (with some extra information) to a csv output file (named beaufort.csv).

Velocities conversion to Beaufort per hour

file: translator.cpp

This program determines Beaufort wind codes based on the wind's velocities values of the last hour. The input data usually come with a few seconds long time intervals, so firstly it finds the minute's average speed and then holds this value in a container. When the timestamps in the container complete an hour period the program calculates the moving average wind velocity.

Input

It takes as input a file with timestamp, velocity pairs in format: yyyy-mm-dd hh:mm:ss,velocity

Moving mean

In statistics, a moving average (moving mean, rolling average or running average) is a calculation to analyze data points by creating a series of averages of different subsets of the full data set. It is the calculation of the mean over the last k data-points.

source: https://en.wikipedia.org/wiki/Moving_average

Structures

MovingMean calculates a moving average of a series of double values

To calculate the moving mean of velocities, we need a container to hold the velocities of an hourly period and after the calculation of MM to remove the first velocity entered to this container. In order to get space complexity: O(1), a std::vector is used as a fixed size queue.

• This queue of length N can be defined by the constructor MovingMean(int N). No need for implicitly-defined destructor, all members have trivial destructors.
• push() adds a new element at the last valid position by wrapping around to the size of the queue. This means that it adds at (front + num_of_elements_in_the_Q)mod(size_of_Q) position.
• pop() returns the value which is pointed by the front member. To keep constant size for the queue, pop() does not delete any item, it lets it to be overwritten by push().
• is_queue_full() checks if there is any valid space to be overwritten by push().
• calculate_MA() calculates a moving average velocity per hour. There is an optional argument bool calc_MM (defaulted as false). When is assigned as true, calculates the MM independently of the passed time.

MinuteVelocity finds the minute's average speed

• An std::unordered_set named seconds_velocities keeps the velocities which belong to this minute.
• average_velocity() calculates the average velocity of this minute by taking the values of seconds_velocities set.

HourBeaufort collects and exports the hour's wind information

• It has a MovingMean queue container of fixed size 60.
• The add_velocity(double velocity, std::string current_time) method pushes velocity to the MovingMean queue. If the current_time is after an hour of the HourBeaufort's hour, it calculates the MM for this hour.

Complexities

Time Complexity: O(N)
Space Complexity: O(1)
where

• N stands for the number of timestamp, wind velocity pairs in the input file. The program is processing line by line without using an internal buffer. Furthermore, the operations of the fixed size queue and of the unordered_set have O(1) time complexities.
• fixed size queue in the MovingMean class has constant space complexity.
• unordered_set will probably hold maximum number of 60 values, so it has also constant space complexity.

Compile & run

To generate the market data

python3 wind_timestamps_generator.py <PATH_TO_OUTPUTFILE>

e.g. <PATH_TO_OUTPUTFILE: timestamps.csv

Command line

To compile C++ source files without Makefile

g++ translator.cpp include/velocities_to_beaufort.cpp -Wall -Wextra -o beaufort.x

To run the program

./beaufort.x <PATH_TO_INPUTFILE>

Makefile

To compile the C++ source files

make

To run the program

make run arg=<PATH_TO_INPUTFILE>

To remove the ELF

make clean

note: PATH_TO_INPUTFILE = PATH_TO_OUTPUTFILE