frc971/zeroing/zeroing.cc

#include "frc971/zeroing/zeroing.h"

#include <cmath>
#include <vector>
#include <algorithm>

#include "frc971/zeroing/wrap.h"


namespace frc971 {
namespace zeroing {
namespace {

bool compare_encoder(const PotAndAbsolutePosition &left,
                     const PotAndAbsolutePosition &right) {
  return left.encoder < right.encoder;
}

}  // namespace

void PopulateEstimatorState(
    const zeroing::PotAndIndexPulseZeroingEstimator &estimator,
    EstimatorState *state) {
  state->error = estimator.error();
  state->zeroed = estimator.zeroed();
  state->position = estimator.position();
  state->pot_position = estimator.filtered_position();
}

void PopulateEstimatorState(
    const zeroing::PotAndAbsEncoderZeroingEstimator &estimator,
    AbsoluteEstimatorState *state) {
  state->error = estimator.error();
  state->zeroed = estimator.zeroed();

  state->position = estimator.position();
  state->pot_position = estimator.filtered_position();
}

PotAndIndexPulseZeroingEstimator::PotAndIndexPulseZeroingEstimator(
    const constants::PotAndIndexPulseZeroingConstants &constants)
    : constants_(constants) {
  start_pos_samples_.reserve(constants_.average_filter_size);
  Reset();
}

void PotAndIndexPulseZeroingEstimator::Reset() {
  samples_idx_ = 0;
  start_pos_ = 0;
  start_pos_samples_.clear();
  zeroed_ = false;
  wait_for_index_pulse_ = true;
  last_used_index_pulse_count_ = 0;
  first_start_pos_ = 0.0;
  error_ = false;
}

void PotAndIndexPulseZeroingEstimator::TriggerError() {
  if (!error_) {
    LOG(ERROR, "Manually triggered zeroing error.\n");
    error_ = true;
  }
}

double PotAndIndexPulseZeroingEstimator::CalculateStartPosition(
    double start_average, double latched_encoder) const {
  // We calculate an aproximation of the value of the last index position.
  // Also account for index pulses not lining up with integer multiples of the
  // index_diff.
  double index_pos =
      start_average + latched_encoder - constants_.measured_index_position;
  // We round index_pos to the closest valid value of the index.
  double accurate_index_pos = (round(index_pos / constants_.index_difference)) *
                              constants_.index_difference;
  // Now we reverse the first calculation to get the accurate start position.
  return accurate_index_pos - latched_encoder +
         constants_.measured_index_position;
}

void PotAndIndexPulseZeroingEstimator::UpdateEstimate(
    const PotAndIndexPosition &info) {
  // We want to make sure that we encounter at least one index pulse while
  // zeroing. So we take the index pulse count from the first sample after
  // reset and wait for that count to change before we consider ourselves
  // zeroed.
  if (wait_for_index_pulse_) {
    last_used_index_pulse_count_ = info.index_pulses;
    wait_for_index_pulse_ = false;
  }

  if (start_pos_samples_.size() < constants_.average_filter_size) {
    start_pos_samples_.push_back(info.pot - info.encoder);
  } else {
    start_pos_samples_[samples_idx_] = info.pot - info.encoder;
  }

  // Drop the oldest sample when we run this function the next time around.
  samples_idx_ = (samples_idx_ + 1) % constants_.average_filter_size;

  double sample_sum = 0.0;

  for (size_t i = 0; i < start_pos_samples_.size(); ++i) {
    sample_sum += start_pos_samples_[i];
  }

  // Calculates the average of the starting position.
  double start_average = sample_sum / start_pos_samples_.size();

  // If there are no index pulses to use or we don't have enough samples yet to
  // have a well-filtered starting position then we use the filtered value as
  // our best guess.
  if (!zeroed_ &&
      (info.index_pulses == last_used_index_pulse_count_ || !offset_ready())) {
    start_pos_ = start_average;
  } else if (!zeroed_ || last_used_index_pulse_count_ != info.index_pulses) {
    // Note the accurate start position and the current index pulse count so
    // that we only run this logic once per index pulse. That should be more
    // resilient to corrupted intermediate data.
    start_pos_ = CalculateStartPosition(start_average, info.latched_encoder);
    last_used_index_pulse_count_ = info.index_pulses;

    // TODO(austin): Reject encoder positions which have x% error rather than
    // rounding to the closest index pulse.

    // Save the first starting position.
    if (!zeroed_) {
      first_start_pos_ = start_pos_;
      LOG(INFO, "latching start position %f\n", first_start_pos_);
    }

    // Now that we have an accurate starting position we can consider ourselves
    // zeroed.
    zeroed_ = true;
    // Throw an error if first_start_pos is bigger/smaller than
    // constants_.allowable_encoder_error * index_diff + start_pos.
    if (::std::abs(first_start_pos_ - start_pos_) >
        constants_.allowable_encoder_error * constants_.index_difference) {
      if (!error_) {
        LOG(ERROR,
            "Encoder ticks out of range since last index pulse. first start "
            "position: %f recent starting position: %f, allowable error: %f\n",
            first_start_pos_, start_pos_,
            constants_.allowable_encoder_error * constants_.index_difference);
        error_ = true;
      }
    }
  }

  position_ = start_pos_ + info.encoder;
  filtered_position_ = start_average + info.encoder;
}

PotAndAbsEncoderZeroingEstimator::PotAndAbsEncoderZeroingEstimator(
    const constants::PotAndAbsoluteEncoderZeroingConstants &constants)
    : constants_(constants) {
  relative_to_absolute_offset_samples_.reserve(constants_.average_filter_size);
  offset_samples_.reserve(constants_.average_filter_size);
  Reset();
}

void PotAndAbsEncoderZeroingEstimator::Reset() {
  zeroed_ = false;
  relative_to_absolute_offset_samples_.clear();
  offset_samples_.clear();
  buffered_samples_.clear();
}

// So, this needs to be a multistep process.  We need to first estimate the
// offset between the absolute encoder and the relative encoder.  That process
// should get us an absolute number which is off by integer multiples of the
// distance/rev.  In parallel, we can estimate the offset between the pot and
// encoder.  When both estimates have converged, we can then compute the offset
// in a cycle, and which cycle, which gives us the accurate global offset.
//
// It's tricky to compute the offset between the absolute and relative encoder.
// We need to compute this inside 1 revolution.  The easiest way to do this
// would be to wrap the encoder, subtract the two of them, and then average the
// result.  That will struggle when they are off by PI.  Instead, we need to
// wrap the number to +- PI from the current averaged offset.
//
// To guard against the robot moving while updating estimates, buffer a number
// of samples and check that the buffered samples are not different than the
// zeroing threshold. At any point that the samples differ too much, do not
// update estimates based on those samples.
void PotAndAbsEncoderZeroingEstimator::UpdateEstimate(
    const PotAndAbsolutePosition &info) {
  // Check for Abs Encoder NaN value that would mess up the rest of the zeroing
  // code below. NaN values are given when the Absolute Encoder is disconnected.
  if (::std::isnan(info.absolute_encoder)) {
    error_ = true;
    return;
  }

  bool moving = true;
  if (buffered_samples_.size() < constants_.moving_buffer_size) {
    // Not enough samples to start determining if the robot is moving or not,
    // don't use the samples yet.
    buffered_samples_.push_back(info);
  } else {
    // Have enough samples to start determining if the robot is moving or not.
    buffered_samples_[buffered_samples_idx_] = info;
    auto max_value =
        ::std::max_element(buffered_samples_.begin(), buffered_samples_.end(),
                           compare_encoder)
            ->encoder;
    auto min_value =
        ::std::min_element(buffered_samples_.begin(), buffered_samples_.end(),
                           compare_encoder)
            ->encoder;
    if (::std::abs(max_value - min_value) < constants_.zeroing_threshold) {
      // Robot isn't moving, use middle sample to determine offsets.
      moving = false;
    }
  }
  buffered_samples_idx_ =
      (buffered_samples_idx_ + 1) % constants_.moving_buffer_size;

  if (!moving) {
    // The robot is not moving, use the middle sample to determine offsets.
    const int middle_index =
        (buffered_samples_idx_ + (constants_.moving_buffer_size - 1) / 2) %
        constants_.moving_buffer_size;

    // Compute the sum of all the offset samples.
    double relative_to_absolute_offset_sum = 0.0;
    for (size_t i = 0; i < relative_to_absolute_offset_samples_.size(); ++i) {
      relative_to_absolute_offset_sum +=
          relative_to_absolute_offset_samples_[i];
    }

    // Compute the average offset between the absolute encoder and relative
    // encoder.  If we have 0 samples, assume it is 0.
    double average_relative_to_absolute_offset =
        relative_to_absolute_offset_samples_.size() == 0
            ? 0.0
            : relative_to_absolute_offset_sum /
                  relative_to_absolute_offset_samples_.size();

    // Now, compute the nearest absolute encoder value to the offset relative
    // encoder position.
    const double adjusted_absolute_encoder =
        Wrap(buffered_samples_[middle_index].encoder +
                 average_relative_to_absolute_offset,
             buffered_samples_[middle_index].absolute_encoder -
                 constants_.measured_absolute_position,
             constants_.one_revolution_distance);

    const double relative_to_absolute_offset =
        adjusted_absolute_encoder - buffered_samples_[middle_index].encoder;

    // Add the sample and update the average with the new reading.
    const size_t relative_to_absolute_offset_samples_size =
        relative_to_absolute_offset_samples_.size();
    if (relative_to_absolute_offset_samples_size <
        constants_.average_filter_size) {
      average_relative_to_absolute_offset =
          (average_relative_to_absolute_offset *
               relative_to_absolute_offset_samples_size +
           relative_to_absolute_offset) /
          (relative_to_absolute_offset_samples_size + 1);

      relative_to_absolute_offset_samples_.push_back(
          relative_to_absolute_offset);
    } else {
      average_relative_to_absolute_offset -=
          relative_to_absolute_offset_samples_[samples_idx_] /
          relative_to_absolute_offset_samples_size;
      relative_to_absolute_offset_samples_[samples_idx_] =
          relative_to_absolute_offset;
      average_relative_to_absolute_offset +=
          relative_to_absolute_offset /
          relative_to_absolute_offset_samples_size;
    }

    // Now compute the offset between the pot and relative encoder.
    if (offset_samples_.size() < constants_.average_filter_size) {
      offset_samples_.push_back(buffered_samples_[middle_index].pot -
                                buffered_samples_[middle_index].encoder);
    } else {
      offset_samples_[samples_idx_] = buffered_samples_[middle_index].pot -
                                      buffered_samples_[middle_index].encoder;
    }

    // Drop the oldest sample when we run this function the next time around.
    samples_idx_ = (samples_idx_ + 1) % constants_.average_filter_size;

    double pot_relative_encoder_offset_sum = 0.0;
    for (size_t i = 0; i < offset_samples_.size(); ++i) {
      pot_relative_encoder_offset_sum += offset_samples_[i];
    }
    pot_relative_encoder_offset_ =
        pot_relative_encoder_offset_sum / offset_samples_.size();

    offset_ = Wrap(buffered_samples_[middle_index].encoder +
                       pot_relative_encoder_offset_,
                   average_relative_to_absolute_offset +
                       buffered_samples_[middle_index].encoder,
                   constants_.one_revolution_distance) -
              buffered_samples_[middle_index].encoder;
    if (offset_ready()) {
      zeroed_ = true;
    }
  }

  // Update the position.
  filtered_position_ = pot_relative_encoder_offset_ + info.encoder;
  position_ = offset_ + info.encoder;
}

}  // namespace zeroing
}  // namespace frc971