private void ComputeVelocities(TimeSeriesCollection tsc, Func <int, PointF> getCoord, float intervalMilliseconds, bool enableSecondPassFiltering)
{
if (tsc.Length <= 2)
{
TimeSeriesPadder.Pad(tsc[Kinematics.LinearHorizontalVelocity], 1);
return;
}
for (int i = 1; i < tsc.Length - 1; i++)
{
PointF a = getCoord(i - 1);
PointF b = getCoord(i + 1);
float t = intervalMilliseconds * 2;
tsc[Kinematics.LinearHorizontalVelocity][i] = (b.X - a.X) / t;
}
TimeSeriesPadder.Pad(tsc[Kinematics.LinearHorizontalVelocity], 1);
// Second pass: apply extra smoothing to the derivatives.
// This is only applied for high speed videos where the digitization is very noisy
// due to the combination of increased time resolution and decreased spatial resolution.
if (enableSecondPassFiltering)
{
double constantVelocitySpan = 40;
MovingAverage filter = new MovingAverage();
double framerate = 1000 / intervalMilliseconds;
double[] averagedHorizontalVelocity = filter.FilterSamples(tsc[Kinematics.LinearHorizontalVelocity], framerate, constantVelocitySpan, 1);
for (int i = 0; i < tsc.Length; i++)
{
tsc[Kinematics.LinearHorizontalVelocity][i] = averagedHorizontalVelocity[i];
}
}
}
private void ComputeAccelerations(TimeSeriesCollection tsc, Func <int, PointF> getCoord, float intervalMilliseconds, bool enableSecondPassFiltering)
{
if (tsc.Length <= 4)
{
TimeSeriesPadder.Pad(tsc[Kinematics.LinearHorizontalAcceleration], 2);
return;
}
// First pass: average speed over 2t centered on each data point.
for (int i = 2; i < tsc.Length - 2; i++)
{
float t = intervalMilliseconds * 2;
double horizontalAcceleration = (tsc[Kinematics.LinearHorizontalVelocity][i + 1] - tsc[Kinematics.LinearHorizontalVelocity][i - 1]) / t;
tsc[Kinematics.LinearHorizontalAcceleration][i] = horizontalAcceleration;
}
TimeSeriesPadder.Pad(tsc[Kinematics.LinearHorizontalAcceleration], 2);
// Second pass: extra smoothing derivatives.
// This is only applied for high speed videos where the digitization is very noisy
// due to the combination of increased time resolution and decreased spatial resolution.
if (enableSecondPassFiltering)
{
double constantAccelerationSpan = 50;
MovingAverage filter = new MovingAverage();
double framerate = 1000 / intervalMilliseconds;
double[] averagedHorizontalAcceleration = filter.FilterSamples(tsc[Kinematics.LinearHorizontalAcceleration], framerate, constantAccelerationSpan, 2);
for (int i = 0; i < tsc.Length; i++)
{
tsc[Kinematics.LinearHorizontalAcceleration][i] = averagedHorizontalAcceleration[i];
}
}
}
