static FirFilterKernelDescription CreateGaussianFilterKernel(double cutoffFrequency, double samplingPeriod, FilterType filterType)
{
double alpha = Math.Sqrt(Math.Log(2.0) / Math.PI);
int windowLength = (int)Math.Ceiling(1.0 / (cutoffFrequency * samplingPeriod));
FirFilterKernelDescription ret = new FirFilterKernelDescription();
ret.Kernel = new double[2 * windowLength + 1];
double normalizationConstant = 0;
double evalConst = -Math.PI * Math.Pow(samplingPeriod * cutoffFrequency / alpha, 2);
for (int i = -windowLength; i <= windowLength; i++)
{
normalizationConstant += Math.Exp(evalConst * i * i);
}
normalizationConstant = 1.0 / normalizationConstant;
ret.Offset = windowLength;
//we use spectral inversion to create a high-pass filter
double sign = (filterType == FilterType.LowPass) ? 1 : -1;
for (int i = 0; i <= windowLength; i++)
{
double value = sign * normalizationConstant * Math.Exp(evalConst * i * i);
ret.Kernel[i + ret.Offset] = value;
ret.Kernel[ret.Offset - i] = value;
}
if (filterType == FilterType.HighPass)
{
ret.Kernel[ret.Offset] += 1;
}
return(ret);
}
FirFilter(FirFilterKernelDescription descr)
{
m_kernelSize = descr.Kernel.Length;
m_kernelDescription = descr;
}