text: /*
   * Copyright 2016 The Cartographer Authors
   *
   * 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.
   */
  
  #ifndef CARTOGRAPHER_MAPPING_3D_SPARSE_POSE_GRAPH_SPA_COST_FUNCTION_H_
  #define CARTOGRAPHER_MAPPING_3D_SPARSE_POSE_GRAPH_SPA_COST_FUNCTION_H_
  
  #include <array>
  
  #include "Eigen/Core"
  #include "Eigen/Geometry"
  #include "cartographer/common/math.h"
  #include "cartographer/mapping/sparse_pose_graph.h"
  #include "cartographer/transform/rigid_transform.h"
  #include "cartographer/transform/transform.h"
  #include "ceres/ceres.h"
  #include "ceres/jet.h"
  
  namespace cartographer {
  namespace mapping_3d {
  namespace sparse_pose_graph {
  
  class SpaCostFunction {
   public:
    using Constraint = mapping::SparsePoseGraph::Constraint;
  
    explicit SpaCostFunction(const Constraint::Pose& pose) : pose_(pose) {}
  
    // Computes the error between the scan-to-submap alignment 'zbar_ij' and the
    // difference of submap pose 'c_i' and scan pose 'c_j' which are both in an
    // arbitrary common frame.
    template <typename T>
    static std::array<T, 6> ComputeUnscaledError(
        const transform::Rigid3d& zbar_ij, const T* const c_i_rotation,
        const T* const c_i_translation, const T* const c_j_rotation,
        const T* const c_j_translation) {
      const Eigen::Quaternion<T> R_i_inverse(c_i_rotation[0], -c_i_rotation[1],
                                             -c_i_rotation[2], -c_i_rotation[3]);
  
      const Eigen::Matrix<T, 3, 1> delta(c_j_translation[0] - c_i_translation[0],
                                         c_j_translation[1] - c_i_translation[1],
                                         c_j_translation[2] - c_i_translation[2]);
      const Eigen::Matrix<T, 3, 1> h_translation = R_i_inverse * delta;
  
      const Eigen::Quaternion<T> h_rotation_inverse =
          Eigen::Quaternion<T>(c_j_rotation[0], -c_j_rotation[1],
                               -c_j_rotation[2], -c_j_rotation[3]) *
          Eigen::Quaternion<T>(c_i_rotation[0], c_i_rotation[1], c_i_rotation[2],
                               c_i_rotation[3]);
  
      const Eigen::Matrix<T, 3, 1> angle_axis_difference =
          transform::RotationQuaternionToAngleAxisVector(
              h_rotation_inverse * zbar_ij.rotation().cast<T>());
  
      return {{T(zbar_ij.translation().x()) - h_translation[0],
               T(zbar_ij.translation().y()) - h_translation[1],
               T(zbar_ij.translation().z()) - h_translation[2],
               angle_axis_difference[0], angle_axis_difference[1],
               angle_axis_difference[2]}};
    }
  
    // Computes the error scaled by 'translation_weight' and 'rotation_weight',
    // storing it in 'e'.
    template <typename T>
    static void ComputeScaledError(const Constraint::Pose& pose,
                                   const T* const c_i_rotation,
                                   const T* const c_i_translation,
                                   const T* const c_j_rotation,
                                   const T* const c_j_translation, T* const e) {
      const std::array<T, 6> e_ij =
          ComputeUnscaledError(pose.zbar_ij, c_i_rotation, c_i_translation,
                               c_j_rotation, c_j_translation);
      for (int ij : {0, 1, 2}) {
        e[ij] = e_ij[ij] * T(pose.translation_weight);
      }
      for (int ij : {3, 4, 5}) {
        e[ij] = e_ij[ij] * T(pose.rotation_weight);
      }
    }
  
    template <typename T>
    bool operator()(const T* const c_i_rotation, const T* const c_i_translation,
                    const T* const c_j_rotation, const T* const c_j_translation,
                    T* const e) const {
      ComputeScaledError(pose_, c_i_rotation, c_i_translation, c_j_rotation,
                         c_j_translation, e);
      return true;
    }
  
   private:
    const Constraint::Pose pose_;
  };
  
  }  // namespace sparse_pose_graph
  }  // namespace mapping_3d
  }  // namespace cartographer
  
  #endif  // CARTOGRAPHER_MAPPING_3D_SPARSE_POSE_GRAPH_SPA_COST_FUNCTION_H_
  