How can i get the radial frequency and the fourie index after FFT？

[ylongwu]

Hi:

   I have a 2D array of real,after FFT I get  a 2D array of complex.

   the question is how can i get the  radial frequency and the fourie index from the complex number?  Mybe the question is so easy,  but i am so confused.  please help me!

[ylongwu]

Hi：

2D array is (s,φ),  where s is a distance and φ a angle.

The sentence is like this

"through the continuous Fourier transform with respect to radial distance s and the Fourier

series with respect to azimuthal angle φ where w is the radial frequency and k is the Fourier

index."  

In fact it is a 2D FFT translate.

[altenbach]

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ylongwu wrote:

2D array is (s,φ),  where s is a distance and φ a angle.

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This is not very clear. Are you talking about the input array or the result array after FFT?

Can you attach a small example that containst your 2D array as a diagram constant?

If you are talking about the input array, Is it a 2D array of complex numbers?

Is it a 2xN 2D array where the first column is [s] and the second column is [φ]?

In any case, you can calculate df from dt and vice versa. The same applies for each dimension in the case of a 2D FFT.

Please claritfy what the problem is. Thanks!

[ylongwu]

Hi ，altenbach

  Thank you  for your help！

  The 2D array (s,φ) is a real array   ,and it is a input array, the first dimension is s and the second  dimension is φ.

 after  FFT to (s,φ)  i get a 2D array of complex number.

  I want to caculate the radial frequency and the fourie index from the complex number.

the following sentence is copied from a treatise:

"through the continuous Fourier transform with respect to radial distance s and the Fourier series with respect to azimuthal angle φ where w is the radial frequency and k is the Fourier index."

After 2D FFT, i should get the  radial frequency "w" and the fourie index"k".

[ylongwu]

the vi

[ylongwu]

the transform is like this：