I'm writing an application that will analyze data from an accelerometer. One of the most important algorithms for this is obviously the FFT, and after much looking I found that Exocortexs library is one of the best for this.
Anyway, when I try to implement it I get this exception:
An unhandled exception of type 'System.ArgumentOutOfRangeException' occurred in Exocortex.DSP.v1.dll
Additional information: must be a power of 2
Here's the code:
class FFT
{
public Exocortex.DSP.ComplexF[] FourierTransform(List<double> vector)
{
//Dictionary<string, List<double>>
int vectorLength = vector.Count;
Exocortex.DSP.ComplexF[] complexData = new Exocortex.DSP.ComplexF[vectorLength];
for (int i = 0; i < vectorLength; ++i)
{
complexData[i].Re = Convert.ToSingle(vector[i]); // Add your real part here
// complexData[i].Im = 2; // Add your imaginary part here
}
Exocortex.DSP.Fourier.FFT(complexData, Exocortex.DSP.FourierDirection.Forward);
return complexData;
(This is really just a version of this example: Fast Fourier Transform in C# ).
The problem might be as simple as the imaginary part of the acceleration since I assume this kind of data is only real but the answer, the FFT that is, is imaginary.
Thanks in advance!
I'm gonna go out on a limb here and suggest that your vectorLength variable is not a a power of 2
.
Try cropping your data such that its new length L = N^2, where integer N > 1.
Does that get ride of the exception?
Are you expecting your signal to be periodic in nature? Is it attached to some mechanism rotating/shaking at fairly steady frequency? If not, what would you hope to get out of using an FFT?
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