savitzky_golay_smoother.cpp

// Copyright (c) 2022, Samsung Research America
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License. Reserved.
 
#include <vector>
#include <memory>
#include "nav2_smoother/savitzky_golay_smoother.hpp"
#include "nav2_core/smoother_exceptions.hpp"
 
namespace nav2_smoother
{
using namespace nav2_util::geometry_utils;  // NOLINT
using namespace std::chrono;  // NOLINT
using nav2_util::PathSegment;
 
void SavitzkyGolaySmoother::configure(
  const nav2::LifecycleNode::WeakPtr & parent,
  std::string name, nav2::TransformBuffer::SharedPtr/*tf*/,
  std::shared_ptr<nav2_costmap_2d::CostmapSubscriber>/*costmap_sub*/,
  std::shared_ptr<nav2_costmap_2d::FootprintSubscriber>/*footprint_sub*/)
{
  auto node = parent.lock();
  logger_ = node->get_logger();
 
  do_refinement_ = node->declare_or_get_parameter(
    name + ".do_refinement", true);
  refinement_num_ = node->declare_or_get_parameter(
    name + ".refinement_num", 2);
  enforce_path_inversion_ = node->declare_or_get_parameter(
    name + ".enforce_path_inversion", true);
  window_size_ = node->declare_or_get_parameter(
    name + ".window_size", 7);
  poly_order_ = node->declare_or_get_parameter(
    name + ".poly_order", 3);
 
  if (window_size_ % 2 == 0 || window_size_ <= 2) {
    throw nav2_core::SmootherException(
            "Savitzky-Golay Smoother requires an odd window size of 3 or greater");
  }
  half_window_size_ = (window_size_ - 1) / 2;
  calculateCoefficients();
}
 
// For more details on calculating Savitzky–Golay filter coefficients,
// see: https://www.colmryan.org/posts/savitsky_golay/
void SavitzkyGolaySmoother::calculateCoefficients()
{
  // We construct the Vandermonde matrix here
  Eigen::VectorXd v = Eigen::VectorXd::LinSpaced(
    window_size_, -half_window_size_,
    half_window_size_);
  Eigen::MatrixXd x = Eigen::MatrixXd::Ones(window_size_, poly_order_ + 1);
  for (int i = 1; i <= poly_order_; i++) {
    x.col(i) = (x.col(i - 1).array() * v.array()).matrix();
  }
  // Compute the pseudoinverse of X, (X^T * X)^-1 * X^T
  Eigen::MatrixXd coeff_mat = (x.transpose() * x).inverse() * x.transpose();
 
  // Extract the smoothing coefficients
  sg_coeffs_ = coeff_mat.row(0).transpose();
}
 
bool SavitzkyGolaySmoother::smooth(
  nav_msgs::msg::Path & path,
  const rclcpp::Duration & max_time)
{
  steady_clock::time_point start = steady_clock::now();
  double time_remaining = max_time.seconds();
 
  bool success = true, reversing_segment;
  nav_msgs::msg::Path curr_path_segment;
  curr_path_segment.header = path.header;
 
  std::vector<PathSegment> path_segments{
    PathSegment{0u, static_cast<unsigned int>(path.poses.size() - 1)}};
  if (enforce_path_inversion_) {
    path_segments = nav2_util::findDirectionalPathSegments(path);
  }
 
  // Minimum point size to smooth is SG filter size + start + end
  unsigned int minimum_points = window_size_ + 2;
  for (unsigned int i = 0; i != path_segments.size(); i++) {
    if (path_segments[i].end - path_segments[i].start > minimum_points) {
      // Populate path segment
      curr_path_segment.poses.clear();
      std::copy(
        path.poses.begin() + path_segments[i].start,
        path.poses.begin() + path_segments[i].end + 1,
        std::back_inserter(curr_path_segment.poses));
 
      // Make sure we're still able to smooth with time remaining
      steady_clock::time_point now = steady_clock::now();
      time_remaining = max_time.seconds() - duration_cast<duration<double>>(now - start).count();
 
      if (time_remaining <= 0.0) {
        RCLCPP_WARN(
          logger_,
          "Smoothing time exceeded allowed duration of %0.2f.", max_time.seconds());
        throw nav2_core::SmootherTimedOut("Smoothing time exceed allowed duration");
      }
 
      // Smooth path segment
      success = success && smoothImpl(curr_path_segment, reversing_segment);
 
      // Assemble the path changes to the main path
      std::copy(
        curr_path_segment.poses.begin(),
        curr_path_segment.poses.end(),
        path.poses.begin() + path_segments[i].start);
    }
  }
 
  return success;
}
 
bool SavitzkyGolaySmoother::smoothImpl(
  nav_msgs::msg::Path & path,
  bool & reversing_segment)
{
  const unsigned int & path_size = path.poses.size();
 
  // Convert PoseStamped to Eigen
  auto toEigenVec = [](const geometry_msgs::msg::PoseStamped & pose) -> Eigen::Vector2d {
      return {pose.pose.position.x, pose.pose.position.y};
    };
 
  auto applyFilterOverAxes =
    [&](std::vector<geometry_msgs::msg::PoseStamped> & plan_pts,
    const std::vector<Eigen::Vector2d> & init_plan_pts) -> void
    {
      // First point is fixed
      for (unsigned int idx = 1; idx != path_size - 1; idx++) {
        Eigen::Vector2d accum(0.0, 0.0);
 
        for (int j = -half_window_size_; j <= half_window_size_; j++) {
          int path_idx = std::clamp<int>(idx + j, 0, path_size - 1);
          accum += sg_coeffs_(j + half_window_size_) * init_plan_pts[path_idx];
        }
        plan_pts[idx].pose.position.x = accum.x();
        plan_pts[idx].pose.position.y = accum.y();
      }
    };
 
  std::vector<Eigen::Vector2d> initial_path_poses(path.poses.size());
  std::transform(
    path.poses.begin(), path.poses.end(),
    initial_path_poses.begin(), toEigenVec);
  applyFilterOverAxes(path.poses, initial_path_poses);
 
  // Let's do additional refinement, it shouldn't take more than a couple milliseconds
  if (do_refinement_) {
    for (int i = 0; i < refinement_num_; i++) {
      std::vector<Eigen::Vector2d> reined_initial_path_poses(path.poses.size());
      std::transform(
        path.poses.begin(), path.poses.end(),
        reined_initial_path_poses.begin(), toEigenVec);
      applyFilterOverAxes(path.poses, reined_initial_path_poses);
    }
  }
 
  nav2_util::updateApproximatePathOrientations(path, reversing_segment);
  return true;
}
 
}  // namespace nav2_smoother
 
#include "pluginlib/class_list_macros.hpp"
#include "nav2_ros_common/tf2_factories.hpp"
PLUGINLIB_EXPORT_CLASS(nav2_smoother::SavitzkyGolaySmoother, nav2_core::Smoother)