inertia.hpp

#pragma once
 
#ifndef LIBXR_NO_EIGEN
 
#include <Eigen/Core>
#include <Eigen/Dense>
#include <type_traits>
 
#include "transform.hpp"
 
namespace LibXR
{
 
using DefaultScalar = LIBXR_DEFAULT_SCALAR;
 
template <typename Scalar = DefaultScalar>
class Inertia
{
 public:
  Scalar data[9];  
  Scalar mass;     
 
  template <typename T, std::enable_if_t<std::is_same<T, Scalar>::value ||
                                             std::is_same<T, float>::value ||
                                             std::is_same<T, double>::value,
                                         int> = 0>
  explicit Inertia(Scalar m, const T (&values)[9]) : mass(m)
  {
    for (int i = 0; i < 3; i++)
    {
      for (int j = 0; j < 3; j++)
      {
        data[i * 3 + j] = static_cast<Scalar>(values[i * 3 + j]);
      }
    }
  }
 
  template <typename T, std::enable_if_t<std::is_same<T, Scalar>::value ||
                                             std::is_same<T, float>::value ||
                                             std::is_same<T, double>::value,
                                         int> = 0>
  explicit Inertia(Scalar m, const T (&matrix)[3][3]) : mass(m)
  {
    for (int i = 0; i < 3; i++)
    {
      for (int j = 0; j < 3; j++)
      {
        data[i * 3 + j] = static_cast<Scalar>(matrix[i][j]);
      }
    }
  }
 
  Inertia() : mass(0) { memset(data, 0, sizeof(data)); }
 
  template <typename T,
            std::enable_if_t<
                std::is_same<T, float>::value || std::is_same<T, double>::value, int> = 0>
  explicit Inertia(Scalar m, const T (&arr)[6])
      : data{arr[0], -arr[3], -arr[5], -arr[3], arr[1],
             -arr[4], -arr[5], -arr[4], arr[2]},
        mass(m)
  {
  }
 
  Inertia(Scalar m, Scalar xx, Scalar yy, Scalar zz, Scalar xy, Scalar yz, Scalar xz)
      : data{xx, -xy, -xz, -xy, yy, -yz, -xz, -yz, zz}, mass(m)
  {
  }
 
  Inertia(Scalar m, const Eigen::Matrix<Scalar, 3, 3> &R) : mass(m)
  {
    memcpy(data, R.data(), 9 * sizeof(Scalar));
  }
 
  operator Eigen::Matrix<Scalar, 3, 3>() const
  {
    return Eigen::Map<const Eigen::Matrix<Scalar, 3, 3>>(data);
  }
 
  Scalar operator()(int i, int j) const { return data[i + j * 3]; }
 
 
  Eigen::Matrix<Scalar, 3, 3> operator+(const Eigen::Matrix<Scalar, 3, 3> &R) const
  {
    return Eigen::Map<const Eigen::Matrix<Scalar, 3, 3>>(data) + R;
  }
 
  Inertia Translate(const Eigen::Matrix<Scalar, 3, 1> &p) const
  {
    Scalar dx = p(0), dy = p(1), dz = p(2);
    Eigen::Matrix<Scalar, 3, 3> translation_matrix;
    translation_matrix << dy * dy + dz * dz, -dx * dy, -dx * dz, -dx * dy,
        dx * dx + dz * dz, -dy * dz, -dx * dz, -dy * dz, dx * dx + dy * dy;
 
    return Inertia(mass, Eigen::Map<const Eigen::Matrix<Scalar, 3, 3>>(data) +
                             mass * translation_matrix);
  }
 
  Inertia Rotate(const Eigen::Matrix<Scalar, 3, 3> &R) const
  {
    return Inertia(
        mass, R * Eigen::Map<const Eigen::Matrix<Scalar, 3, 3>>(data) * R.transpose());
  }
 
  Inertia Rotate(const RotationMatrix<Scalar> &R) const
  {
    return Rotate(Eigen::Map<const Eigen::Matrix<Scalar, 3, 3>>(R.data_));
  }
 
  Inertia Rotate(const Eigen::Quaternion<Scalar> &q) const
  {
    return Inertia(
        mass, q * Eigen::Map<const Eigen::Matrix<Scalar, 3, 3>>(data) * q.conjugate());
  }
 
  static Eigen::Matrix<Scalar, 3, 3> Rotate(const Eigen::Matrix<Scalar, 3, 3> &R,
                                            const Eigen::Quaternion<Scalar> &q)
  {
    return q * R * q.conjugate();
  }
 
  Inertia Rotate(const Quaternion<Scalar> &q) const
  {
    return Rotate(Eigen::Quaternion<Scalar>(q));
  }
};
 
template <typename Scalar = DefaultScalar>
class CenterOfMass
{
 public:
  Eigen::Matrix<Scalar, 3, 1> position;  
  Scalar mass;                           
 
  CenterOfMass() : position(0., 0., 0.), mass(0.) {}
 
  CenterOfMass(Scalar m, const LibXR::Position<Scalar> &p) : position(p), mass(m) {}
 
  CenterOfMass(Scalar m, const Eigen::Matrix<Scalar, 3, 1> &p) : position(p), mass(m) {}
 
  CenterOfMass(const Inertia<Scalar> &m, const Transform<Scalar> &p)
      : position(p.translation), mass(m.mass)
  {
  }
 
  CenterOfMass operator+(const CenterOfMass &m) const
  {
    Scalar new_mass = mass + m.mass;
    return CenterOfMass(
        new_mass,
        Position<Scalar>((position(0) * mass + m.position(0) * m.mass) / new_mass,
                         (position(1) * mass + m.position(1) * m.mass) / new_mass,
                         (position(2) * mass + m.position(2) * m.mass) / new_mass));
  }
 
  CenterOfMass &operator+=(const CenterOfMass &m)
  {
    *this = *this + m;
    return *this;
  }
};
 
}  // namespace LibXR
 
#endif