public PairDouble evaluateResonanceFrequency(ChartTypes type, SignalUnits targetUnits, double approximationResonanceFrequency = 0.0)
{
int kNumSteps = 4096;
// Only acceleration data is used to estimate the resonance frequency
SignalUnits baseUnits = SignalUnits.UNKNOWN;
if (data[SignalUnits.METERS_PER_SECOND2] != null)
{
baseUnits = SignalUnits.METERS_PER_SECOND2;
}
else if (data.ContainsKey(SignalUnits.METERS_PER_SECOND2_PER_FORCE) && data[SignalUnits.METERS_PER_SECOND2_PER_FORCE] != null)
{
baseUnits = SignalUnits.METERS_PER_SECOND2_PER_FORCE;
}
if (baseUnits == SignalUnits.UNKNOWN)
{
return(null);
}
double[,] complexData = data[baseUnits];
int nData = frequency.Length;
double[] realPart = new double[nData];
double[] imagPart = new double[nData];
for (int i = 0; i != nData; ++i)
{
realPart[i] = complexData[i, 0];
imagPart[i] = complexData[i, 1];
}
LinearSpline splineRealPart = LinearSpline.InterpolateSorted(frequency, realPart);
LinearSpline splineImagPart = LinearSpline.InterpolateSorted(frequency, imagPart);
List <double> resFrequencies = null;
Func <double, double> fun = null;
Func <double, double> diffFun = null;
switch (type)
{
case ChartTypes.REAL_FREQUENCY:
fun = x => splineRealPart.Interpolate(x);
diffFun = x => splineRealPart.Differentiate(x);
break;
case ChartTypes.IMAG_FREQUENCY:
fun = x => splineImagPart.Differentiate(x);
diffFun = x => splineImagPart.Differentiate2(x);
break;
}
if (fun == null || diffFun == null)
{
return(null);
}
double startFrequency = frequency[0];
double endFrequency = frequency[nData - 1];
resFrequencies = findAllRootsBisection(fun, startFrequency, endFrequency, kNumSteps);
if (resFrequencies == null || resFrequencies.Count == 0)
{
return(null);
}
double distance;
double minDistance = Double.MaxValue;
int indClosestResonance = 0;
int numFrequencies = resFrequencies.Count;
for (int i = 0; i != numFrequencies; ++i)
{
try
{
resFrequencies[i] = NewtonRaphson.FindRootNearGuess(fun, diffFun, resFrequencies[i], startFrequency, endFrequency);
}
catch
{
}
distance = Math.Abs(resFrequencies[i] - approximationResonanceFrequency);
if (distance < minDistance)
{
minDistance = distance;
indClosestResonance = i;
}
}
double resonanceFrequency = resFrequencies[indClosestResonance];
// Evaluate the amplitude value by using data of the target type
if (baseUnits != targetUnits)
{
complexData = data[targetUnits];
for (int i = 0; i != nData; ++i)
{
realPart[i] = complexData[i, 0];
imagPart[i] = complexData[i, 1];
}
splineRealPart = LinearSpline.InterpolateSorted(frequency, realPart);
splineImagPart = LinearSpline.InterpolateSorted(frequency, imagPart);
}
double realPeak = splineRealPart.Interpolate(resonanceFrequency);
double imagPeak = splineImagPart.Interpolate(resonanceFrequency);
double ampPeak = Math.Sqrt(Math.Pow(realPeak, 2.0) + Math.Pow(imagPeak, 2.0));
return(new PairDouble(resonanceFrequency, ampPeak));
}