Umeyama.h

// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 2009 Hauke Heibel <hauke.heibel@gmail.com>
//
// This Source Code Form is subject to the terms of the Mozilla
// Public License v. 2.0. If a copy of the MPL was not distributed
// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.

#ifndef EIGEN_UMEYAMA_H
#define EIGEN_UMEYAMA_H

// This file requires the user to include
// * Eigen/Core
// * Eigen/LU
// * Eigen/SVD
// * Eigen/Array

// IWYU pragma: private
#include "./InternalHeaderCheck.h"

namespace Eigen {

// These helpers are required since it allows to use mixed types as parameters
// for the Umeyama. The problem with mixed parameters is that the return type
// cannot trivially be deduced when float and double types are mixed.
namespace internal {

// Compile time return type deduction for different MatrixBase types.
// Different means here different alignment and parameters but the same underlying
// real scalar type.
template <typename MatrixType, typename OtherMatrixType>
struct umeyama_transform_matrix_type {
  enum {
    MinRowsAtCompileTime =
        internal::min_size_prefer_dynamic(MatrixType::RowsAtCompileTime, OtherMatrixType::RowsAtCompileTime),

    // When possible we want to choose some small fixed size value since the result
    // is likely to fit on the stack. So here, min_size_prefer_dynamic is not what we want.
    HomogeneousDimension = int(MinRowsAtCompileTime) == Dynamic ? Dynamic : int(MinRowsAtCompileTime) + 1
  };

  typedef Matrix<typename traits<MatrixType>::Scalar, HomogeneousDimension, HomogeneousDimension,
                 AutoAlign | (traits<MatrixType>::Flags & RowMajorBit ? RowMajor : ColMajor), HomogeneousDimension,
                 HomogeneousDimension>
      type;
};

}  // namespace internal

template <typename Derived, typename OtherDerived>
typename internal::umeyama_transform_matrix_type<Derived, OtherDerived>::type umeyama(
    const MatrixBase<Derived>& src, const MatrixBase<OtherDerived>& dst, bool with_scaling = true) {
  typedef typename internal::umeyama_transform_matrix_type<Derived, OtherDerived>::type TransformationMatrixType;
  typedef typename internal::traits<TransformationMatrixType>::Scalar Scalar;
  typedef typename NumTraits<Scalar>::Real RealScalar;

  EIGEN_STATIC_ASSERT(!NumTraits<Scalar>::IsComplex, NUMERIC_TYPE_MUST_BE_REAL)
  EIGEN_STATIC_ASSERT(
      (internal::is_same<Scalar, typename internal::traits<OtherDerived>::Scalar>::value),
      YOU_MIXED_DIFFERENT_NUMERIC_TYPES__YOU_NEED_TO_USE_THE_CAST_METHOD_OF_MATRIXBASE_TO_CAST_NUMERIC_TYPES_EXPLICITLY)

  enum { Dimension = internal::min_size_prefer_dynamic(Derived::RowsAtCompileTime, OtherDerived::RowsAtCompileTime) };

  typedef Matrix<Scalar, Dimension, 1> VectorType;
  typedef Matrix<Scalar, Dimension, Dimension> MatrixType;
  typedef typename internal::plain_matrix_type_row_major<Derived>::type RowMajorMatrixType;

  const Index m = src.rows();  // dimension
  const Index n = src.cols();  // number of measurements

  // required for demeaning ...
  const RealScalar one_over_n = RealScalar(1) / static_cast<RealScalar>(n);

  // computation of mean
  const VectorType src_mean = src.rowwise().sum() * one_over_n;
  const VectorType dst_mean = dst.rowwise().sum() * one_over_n;

  // demeaning of src and dst points
  const RowMajorMatrixType src_demean = src.colwise() - src_mean;
  const RowMajorMatrixType dst_demean = dst.colwise() - dst_mean;

  // Eq. (38)
  const MatrixType sigma = one_over_n * dst_demean * src_demean.transpose();

  JacobiSVD<MatrixType, ComputeFullU | ComputeFullV> svd(sigma);

  // Initialize the resulting transformation with an identity matrix...
  TransformationMatrixType Rt = TransformationMatrixType::Identity(m + 1, m + 1);

  // Eq. (39)
  VectorType S = VectorType::Ones(m);

  if (svd.matrixU().determinant() * svd.matrixV().determinant() < 0) {
    Index tmp = m - 1;
    S(tmp) = -1;
  }

  // Eq. (40) and (43)
  Rt.block(0, 0, m, m).noalias() = svd.matrixU() * S.asDiagonal() * svd.matrixV().transpose();

  if (with_scaling) {
    // Eq. (36)-(37)
    const Scalar src_var = src_demean.rowwise().squaredNorm().sum() * one_over_n;

    // Eq. (42)
    const Scalar c = Scalar(1) / src_var * svd.singularValues().dot(S);

    // Eq. (41)
    Rt.col(m).head(m) = dst_mean;
    Rt.col(m).head(m).noalias() -= c * Rt.topLeftCorner(m, m) * src_mean;
    Rt.block(0, 0, m, m) *= c;
  } else {
    Rt.col(m).head(m) = dst_mean;
    Rt.col(m).head(m).noalias() -= Rt.topLeftCorner(m, m) * src_mean;
  }

  return Rt;
}

}  // end namespace Eigen

#endif  // EIGEN_UMEYAMA_H