I am trying to find the vibrations and the frequency of the spectrum of the waveform generated by a vector of data representing the movement of a pixel in an image.
Data is saved in a .txt file as follows:
75.000000
60.000000
52.000000
61.000000
66.000000
78.000000
86.000000
74.000000
59.000000
47.000000
58.000000
60.000000
81.000000
85.000000
81.000000
70.000000
58.000000
59.000000
56.000000
61.000000
77.000000
88.000000
82.000000
79.000000
75.000000
75.000000
75.000000
75.000000
76.000000
82.000000
82.000000
The idea is to find the oscillation frequency (Hz) and the frequency spectrum (amplitude) of the graph obtained from the data, an example of the graph is given below.
I read a lot and talked a lot about using the fftw3 library for Fourier analysis, I am new to using C ++ and even most of this library.
Hope you can help me with code or ideas to solve my problem.
Many thanks for your help.
I am working with Microsoft Visual C ++ 2010 (win32)
the code:
#include "StdAfx.h"
#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <fftw3.h>
#include <iostream>
#include <cmath>
#include <fstream>
#include <string>
#include <vector>
using namespace std;
int main()
{
int i;
const int N=100;
double Fs=200;
double dF=Fs/N;
double T=1/Fs;
double f=86;
double *in;
fftw_complex *out;
double ff[N];
fftw_plan plan_forward;
in = (double*) fftw_malloc(sizeof(double) * N);
out = (fftw_complex*) fftw_malloc(sizeof(fftw_complex) * N);
std::ifstream myfile ("Vetor_Oscilacao2.txt");
if (myfile.is_open())
{
std::vector<double> in;
std::string line;
while (std::getline(myfile, line))
{
double value = std::stod(line);
std::cout << value << '\n';
in.push_back(value);
}
myfile.close();
}
else
std::cout << "Unable to open file";
std::cin.get();
for (int i=0; i<= ((N/2)-1);i++)
{
ff[i]=Fs*i/N;
}
plan_forward = fftw_plan_dft_r2c_1d ( N, in, out, FFTW_ESTIMATE );
fftw_execute ( plan_forward );
double v[N];
for (int i = 0; i<= ((N/2)-1); i++)
{
v[i]=(10*log(sqrt(out[i][0]*out[i][0]+ out[i][1]*out[i][1])))/N;
}
fstream fichero;
fichero.open("example2.txt",fstream::out);
fichero << "plot '-' using 1:2" << std::endl;
for(i = 0;i< ((N/2)-1); i++)
{
fichero << ff[i]<< " " << v[i]<< std::endl;
}
fichero.close();
fftw_destroy_plan (plan_forward);
fftw_free (in);
fftw_free (out);
return 0;
}