AW: [Insight-users] Urgent: How to compute Fourier Decomposition of signal in ITK?

[Jiang]

Hi Luis,
Thank you very much for your reply and new example.
I read some more materials about Fourier Transform and its relationship
with curve's smoothness. So I understand this method better than before.
In the example FourierDescriptors1.cxx, the magnitude of the Fourier
coefficient in the whole frequency band has been calculated. I should
use it to analysis the smoothness of the target curve. If the magnitude
value is low in high frequency, and high in low frequency, then the
curve is smooth. I didn't check the materials about spectrum analysis in
evaluating the bias of Fourier Spectrum. Is there some good method to
evaluate it? And in the description part of example, it said, the phase
should also be used as analyses. How to get the phase and how to use it
to do the smoothness evaluation?
There is one question about the code of the example. I copy the code as
one function in my class. There are some errors when I compile it. There
is one definition could not be recognized.
typedef vcl_vector< FFTCoefficientType > FFTSpectrumType;
When I change vcl_vector to vnl_vector, the errors disappear. I don't
know why. Is my modification correct? Will it affect the calculation
result? If it was wrong, how could I figure the errors?


Thank you for your all replies and so kind help!


Best regards,

Jiang