vpStatisticalTestEWMA.cpp

/****************************************************************************
 *
 * ViSP, open source Visual Servoing Platform software.
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#include <visp3/core/vpStatisticalTestEWMA.h>
 
void vpStatisticalTestEWMA::computeDeltaAndLimits()
{
  float delta = 3.f * m_stdev * std::sqrt(m_alpha / (2.f - m_alpha));
  m_limitDown = m_mean - delta;
  m_limitUp = m_mean + delta;
}
 
vpStatisticalTestAbstract::vpMeanDriftType vpStatisticalTestEWMA::detectDownwardMeanDrift()
{
  if (m_wt <= m_limitDown) {
    return MEAN_DRIFT_DOWNWARD;
  }
  else {
    return MEAN_DRIFT_NONE;
  }
}
 
vpStatisticalTestAbstract::vpMeanDriftType vpStatisticalTestEWMA::detectUpwardMeanDrift()
{
  if (m_wt >= m_limitUp) {
    return MEAN_DRIFT_UPWARD;
  }
  else {
    return MEAN_DRIFT_NONE;
  }
}
 
bool vpStatisticalTestEWMA::updateStatistics(const float &signal)
{
  bool areStatsReady = vpStatisticalTestAbstract::updateStatistics(signal);
  if (areStatsReady) {
    // Computation of the limits
    computeDeltaAndLimits();
 
    // Initialize first value
    m_wt = m_mean;
  }
  return areStatsReady;
}
 
void vpStatisticalTestEWMA::updateTestSignals(const float &signal)
{
  // Update last value
  m_wtprev = m_wt;
// w(t) = alpha * s(t) + (1 - alpha) * w(t- 1);
  m_wt = m_wtprev +  m_alpha * (signal - m_wtprev);
}
 
vpStatisticalTestEWMA::vpStatisticalTestEWMA(const float &alpha)
  : vpStatisticalTestAbstract()
  , m_alpha(0.f)
  , m_wt(0.f)
  , m_wtprev(0.f)
{
  init(alpha);
}
 
void vpStatisticalTestEWMA::init(const float &alpha)
{
  vpStatisticalTestAbstract::init();
  m_alpha = alpha;
  unsigned int nbRequiredSamples = static_cast<unsigned int>(std::ceil(3.f / m_alpha));
  setNbSamplesForStat(nbRequiredSamples);
  m_wt = 0.f;
  m_wtprev = 0.f;
}
 
void vpStatisticalTestEWMA::init(const float &alpha, const float &mean, const float &stdev)
{
  vpStatisticalTestAbstract::init();
  m_alpha = alpha;
  m_mean = mean;
  unsigned int nbRequiredSamples = static_cast<unsigned int>(std::ceil(3.f / m_alpha));
  setNbSamplesForStat(nbRequiredSamples);
  m_stdev = stdev;
  m_wt = mean;
  m_wtprev = 0.f;
 
  // Computation of the limits
  computeDeltaAndLimits();
  m_areStatisticsComputed = true;
}
 
void vpStatisticalTestEWMA::setAlpha(const float &alpha)
{
  init(alpha);
}