confused by robott_localization by the process of predict and correct in filter? [closed]

edit

Hello, I am confused by the processMeasurement() function in filter_base.cpp . Both predict and correct use the same measurement ? In normal EKF, I think one measurement is used for predict, another for correct.

 // If we've had a previous reading, then go through the predict/update
// cycle. Otherwise, set our state and covariance to whatever we get
// from this measurement.
if (initialized_)
{
  // Determine how much time has passed since our last measurement
  delta = measurement.time_ - lastMeasurementTime_;

  FB_DEBUG("Filter is already initialized. Carrying out predict/correct loop...\n"
           "Measurement time is " << std::setprecision(20) << measurement.time_ <<
           ", last measurement time is " << lastMeasurementTime_ << ", delta is " << delta << "\n");

  // Only want to carry out a prediction if it's
  // forward in time. Otherwise, just correct.todo  a little confused here, both predict and correct use the same measurement ?
  if (delta > 0)
  {
    validateDelta(delta);
    predict(measurement.time_, delta);

    // Return this to the user
    predictedState_ = state_;//
  }

  correct(measurement);//
}