Rotation3d.hpp

Go to the documentation of this file.

// Copyright (c) FIRST and other WPILib contributors.
// Open Source Software; you can modify and/or share it under the terms of
// the WPILib BSD license file in the root directory of this project.
 
#pragma once
 
#include <numbers>
#include <type_traits>
 
#include <Eigen/Core>
#include <gcem.hpp>
 
#include "wpi/math/geometry/Quaternion.hpp"
#include "wpi/math/geometry/Rotation2d.hpp"
#include "wpi/math/linalg/ct_matrix.hpp"
#include "wpi/units/angle.hpp"
#include "wpi/units/math.hpp"
#include "wpi/util/MathExtras.hpp"
#include "wpi/util/SymbolExports.hpp"
 
namespace wpi::util {
class json;
}  // namespace wpi::util
 
namespace wpi::math {
 
/**
 * A rotation in a 3D coordinate frame, represented by a quaternion. Note that
 * unlike 2D rotations, 3D rotations are not always commutative, so changing the
 * order of rotations changes the result.
 *
 * As an example of the order of rotations mattering, suppose we have a card
 * that looks like this:
 *
 * <pre>
 *          ┌───┐        ┌───┐
 *          │ X │        │ x │
 *   Front: │ | │  Back: │ · │
 *          │ | │        │ · │
 *          └───┘        └───┘
 * </pre>
 *
 * If we rotate 90º clockwise around the axis into the page, then flip around
 * the left/right axis, we get one result:
 *
 * <pre>
 *   ┌───┐
 *   │ X │   ┌───────┐   ┌───────┐
 *   │ | │ → │------X│ → │······x│
 *   │ | │   └───────┘   └───────┘
 *   └───┘
 * </pre>
 *
 * If we flip around the left/right axis, then rotate 90º clockwise around the
 * axis into the page, we get a different result:
 *
 * <pre>
 *   ┌───┐   ┌───┐
 *   │ X │   │ · │   ┌───────┐
 *   │ | │ → │ · │ → │x······│
 *   │ | │   │ x │   └───────┘
 *   └───┘   └───┘
 * </pre>
 *
 * Because order matters for 3D rotations, we need to distinguish between
 * <em>extrinsic</em> rotations and <em>intrinsic</em> rotations. Rotating
 * extrinsically means rotating around the global axes, while rotating
 * intrinsically means rotating from the perspective of the other rotation. A
 * neat property is that applying a series of rotations extrinsically is the
 * same as applying the same series in the opposite order intrinsically.
 */
class WPILIB_DLLEXPORT Rotation3d final {
 public:
  /**
   * Constructs a Rotation3d representing no rotation.
   */
  constexpr Rotation3d() = default;
 
  /**
   * Constructs a Rotation3d from a quaternion.
   *
   * @param q The quaternion.
   */
  constexpr explicit Rotation3d(const Quaternion& q) { m_q = q.Normalize(); }
 
  /**
   * Constructs a Rotation3d from extrinsic roll, pitch, and yaw.
   *
   * Extrinsic rotations occur in that order around the axes in the fixed global
   * frame rather than the body frame.
   *
   * Angles are measured counterclockwise with the rotation axis pointing "out
   * of the page". If you point your right thumb along the positive axis
   * direction, your fingers curl in the direction of positive rotation.
   *
   * @param roll The counterclockwise rotation angle around the X axis (roll).
   * @param pitch The counterclockwise rotation angle around the Y axis (pitch).
   * @param yaw The counterclockwise rotation angle around the Z axis (yaw).
   */
  constexpr Rotation3d(wpi::units::radian_t roll, wpi::units::radian_t pitch,
                       wpi::units::radian_t yaw) {
    // https://en.wikipedia.org/wiki/Conversion_between_quaternions_and_Euler_angles#Euler_angles_to_quaternion_conversion
    double cr = wpi::units::math::cos(roll * 0.5);
    double sr = wpi::units::math::sin(roll * 0.5);
 
    double cp = wpi::units::math::cos(pitch * 0.5);
    double sp = wpi::units::math::sin(pitch * 0.5);
 
    double cy = wpi::units::math::cos(yaw * 0.5);
    double sy = wpi::units::math::sin(yaw * 0.5);
 
    m_q = Quaternion{cr * cp * cy + sr * sp * sy, sr * cp * cy - cr * sp * sy,
                     cr * sp * cy + sr * cp * sy, cr * cp * sy - sr * sp * cy};
  }
 
  /**
   * Constructs a Rotation3d with the given axis-angle representation. The axis
   * doesn't have to be normalized.
   *
   * @param axis The rotation axis.
   * @param angle The rotation around the axis.
   */
  constexpr Rotation3d(const Eigen::Vector3d& axis,
                       wpi::units::radian_t angle) {
    double norm = ct_matrix{axis}.norm();
    if (norm == 0.0) {
      return;
    }
 
    // https://en.wikipedia.org/wiki/Conversion_between_quaternions_and_Euler_angles#Definition
    Eigen::Vector3d v{{axis(0) / norm * wpi::units::math::sin(angle / 2.0),
                       axis(1) / norm * wpi::units::math::sin(angle / 2.0),
                       axis(2) / norm * wpi::units::math::sin(angle / 2.0)}};
    m_q = Quaternion{wpi::units::math::cos(angle / 2.0), v(0), v(1), v(2)};
  }
 
  /**
   * Constructs a Rotation3d with the given rotation vector representation. This
   * representation is equivalent to axis-angle, where the normalized axis is
   * multiplied by the rotation around the axis in radians.
   *
   * @param rvec The rotation vector.
   */
  constexpr explicit Rotation3d(const Eigen::Vector3d& rvec)
      : Rotation3d{rvec, wpi::units::radian_t{ct_matrix{rvec}.norm()}} {}
 
  /**
   * Constructs a Rotation3d from a rotation matrix.
   *
   * @param rotationMatrix The rotation matrix.
   * @throws std::domain_error if the rotation matrix isn't special orthogonal.
   */
  constexpr explicit Rotation3d(const Eigen::Matrix3d& rotationMatrix) {
    auto impl = []<typename Matrix3d>(const Matrix3d& R) -> Quaternion {
      // Require that the rotation matrix is special orthogonal. This is true if
      // the matrix is orthogonal (RRᵀ = I) and normalized (determinant is 1).
      if ((R * R.transpose() - Matrix3d::Identity()).norm() > 1e-9) {
        throw std::domain_error("Rotation matrix isn't orthogonal");
      }
      // HACK: Uses ct_matrix instead of <Eigen/LU> for determinant because
      //       including <Eigen/LU> doubles compilation times on MSVC, even if
      //       this constructor is unused. MSVC's frontend inefficiently parses
      //       large headers; GCC and Clang are largely unaffected.
      if (gcem::abs(ct_matrix{R}.determinant() - 1.0) > 1e-9) {
        throw std::domain_error(
            "Rotation matrix is orthogonal but not special orthogonal");
      }
 
      // Turn rotation matrix into a quaternion
      // https://www.euclideanspace.com/maths/geometry/rotations/conversions/matrixToQuaternion/
      double trace = R(0, 0) + R(1, 1) + R(2, 2);
      double w;
      double x;
      double y;
      double z;
 
      if (trace > 0.0) {
        double s = 0.5 / gcem::sqrt(trace + 1.0);
        w = 0.25 / s;
        x = (R(2, 1) - R(1, 2)) * s;
        y = (R(0, 2) - R(2, 0)) * s;
        z = (R(1, 0) - R(0, 1)) * s;
      } else {
        if (R(0, 0) > R(1, 1) && R(0, 0) > R(2, 2)) {
          double s = 2.0 * gcem::sqrt(1.0 + R(0, 0) - R(1, 1) - R(2, 2));
          w = (R(2, 1) - R(1, 2)) / s;
          x = 0.25 * s;
          y = (R(0, 1) + R(1, 0)) / s;
          z = (R(0, 2) + R(2, 0)) / s;
        } else if (R(1, 1) > R(2, 2)) {
          double s = 2.0 * gcem::sqrt(1.0 + R(1, 1) - R(0, 0) - R(2, 2));
          w = (R(0, 2) - R(2, 0)) / s;
          x = (R(0, 1) + R(1, 0)) / s;
          y = 0.25 * s;
          z = (R(1, 2) + R(2, 1)) / s;
        } else {
          double s = 2.0 * gcem::sqrt(1.0 + R(2, 2) - R(0, 0) - R(1, 1));
          w = (R(1, 0) - R(0, 1)) / s;
          x = (R(0, 2) + R(2, 0)) / s;
          y = (R(1, 2) + R(2, 1)) / s;
          z = 0.25 * s;
        }
      }
 
      return Quaternion{w, x, y, z};
    };
 
    if (std::is_constant_evaluated()) {
      m_q = impl(ct_matrix3d{rotationMatrix});
    } else {
      m_q = impl(rotationMatrix);
    }
  }
 
  /**
   * Constructs a Rotation3d that rotates the initial vector onto the final
   * vector.
   *
   * This is useful for turning a 3D vector (final) into an orientation relative
   * to a coordinate system vector (initial).
   *
   * @param initial The initial vector.
   * @param final The final vector.
   */
  constexpr Rotation3d(const Eigen::Vector3d& initial,
                       const Eigen::Vector3d& final) {
    double dot = ct_matrix{initial}.dot(ct_matrix{final});
    double normProduct = ct_matrix{initial}.norm() * ct_matrix{final}.norm();
    double dotNorm = dot / normProduct;
 
    if (dotNorm > 1.0 - 1E-9) {
      // If the dot product is 1, the two vectors point in the same direction so
      // there's no rotation. The default initialization of m_q will work.
      return;
    } else if (dotNorm < -1.0 + 1E-9) {
      // If the dot product is -1, the two vectors are antiparallel, so a 180°
      // rotation is required. Any other vector can be used to generate an
      // orthogonal one.
 
      double x = gcem::abs(initial(0));
      double y = gcem::abs(initial(1));
      double z = gcem::abs(initial(2));
 
      // Find vector that is most orthogonal to initial vector
      Eigen::Vector3d other;
      if (x < y) {
        if (x < z) {
          // Use x-axis
          other = Eigen::Vector3d{{1, 0, 0}};
        } else {
          // Use z-axis
          other = Eigen::Vector3d{{0, 0, 1}};
        }
      } else {
        if (y < z) {
          // Use y-axis
          other = Eigen::Vector3d{{0, 1, 0}};
        } else {
          // Use z-axis
          other = Eigen::Vector3d{{0, 0, 1}};
        }
      }
 
      auto axis = ct_matrix{initial}.cross(ct_matrix{other});
 
      double axisNorm = axis.norm();
      m_q = Quaternion{0.0, axis(0) / axisNorm, axis(1) / axisNorm,
                       axis(2) / axisNorm};
    } else {
      auto axis = ct_matrix{initial}.cross(final);
 
      // https://stackoverflow.com/a/11741520
      m_q =
          Quaternion{normProduct + dot, axis(0), axis(1), axis(2)}.Normalize();
    }
  }
 
  /**
   * Constructs a 3D rotation from a 2D rotation in the X-Y plane.
   *
   * @param rotation The 2D rotation.
   * @see Pose3d(Pose2d)
   * @see Transform3d(Transform2d)
   */
  constexpr explicit Rotation3d(const Rotation2d& rotation)
      : Rotation3d{0_rad, 0_rad, rotation.Radians()} {}
 
  /**
   * Takes the inverse of the current rotation.
   *
   * @return The inverse of the current rotation.
   */
  constexpr Rotation3d Inverse() const { return Rotation3d{m_q.Inverse()}; }
 
  /**
   * Multiplies the current rotation by a scalar.
   *
   * @param scalar The scalar.
   *
   * @return The new scaled Rotation3d.
   */
  constexpr Rotation3d operator*(double scalar) const {
    return Rotation3d{}.Interpolate(*this, scalar);
  }
 
  /**
   * Divides the current rotation by a scalar.
   *
   * @param scalar The scalar.
   *
   * @return The new scaled Rotation3d.
   */
  constexpr Rotation3d operator/(double scalar) const {
    return *this * (1.0 / scalar);
  }
 
  /**
   * Checks equality between this Rotation3d and another object.
   */
  constexpr bool operator==(const Rotation3d& other) const {
    return gcem::abs(gcem::abs(m_q.Dot(other.m_q)) -
                     m_q.Norm() * other.m_q.Norm()) < 1e-9;
  }
 
  /**
   * Adds the new rotation to the current rotation. The other rotation is
   * applied extrinsically, which means that it rotates around the global axes.
   * For example, Rotation3d{90_deg, 0, 0}.RotateBy(Rotation3d{0, 45_deg, 0})
   * rotates by 90 degrees around the +X axis and then by 45 degrees around the
   * global +Y axis. (This is equivalent to Rotation3d{90_deg, 45_deg, 0})
   *
   * @param other The extrinsic rotation to rotate by.
   *
   * @return The new rotated Rotation3d.
   */
  constexpr Rotation3d RotateBy(const Rotation3d& other) const {
    return Rotation3d{other.m_q * m_q};
  }
 
  /**
   * Returns the current rotation relative to the given rotation. Because the
   * result is in the perspective of the given rotation, it must be applied
   * intrinsically. See the class comment for definitions of extrinsic and
   * intrinsic rotations.
   *
   * @param other The rotation describing the orientation of the new coordinate
   * frame that the current rotation will be converted into.
   *
   * @return The current rotation relative to the new orientation of the
   * coordinate frame.
   */
  constexpr Rotation3d RelativeTo(const Rotation3d& other) const {
    // To apply a quaternion intrinsically, we must right-multiply by that
    // quaternion. Therefore, "this_q relative to other_q" is the q such that
    // other_q q = this_q:
    //
    //   other_q q = this_q
    //   q = other_q⁻¹ this_q
    return Rotation3d{other.m_q.Inverse() * m_q};
  }
 
  /**
   * Interpolates between this rotation and another.
   *
   * @param endValue The other rotation.
   * @param t How far between the two rotations we are (0 means this rotation, 1
   *     means other rotation).
   * @return The interpolated value.
   */
  constexpr Rotation3d Interpolate(Rotation3d endValue, double t) const {
    // https://en.wikipedia.org/wiki/Slerp#Quaternion_Slerp
    //
    // slerp(q₀, q₁, t) = (q₁q₀⁻¹)ᵗq₀
    //
    // We negate the delta quaternion if necessary to take the shortest path
    const auto& q0 = m_q;
    const auto& q1 = endValue.m_q;
    auto delta = q1 * q0.Inverse();
    if (delta.W() < 0.0) {
      delta = Quaternion{-delta.W(), -delta.X(), -delta.Y(), -delta.Z()};
    }
    return Rotation3d{delta.Pow(t) * q0};
  }
 
  /**
   * Returns the quaternion representation of the Rotation3d.
   */
  constexpr const Quaternion& GetQuaternion() const { return m_q; }
 
  /**
   * Returns the counterclockwise rotation angle around the X axis (roll).
   */
  constexpr wpi::units::radian_t X() const {
    double w = m_q.W();
    double x = m_q.X();
    double y = m_q.Y();
    double z = m_q.Z();
 
    // wpimath/algorithms.md
    double cxcy = 1.0 - 2.0 * (x * x + y * y);
    double sxcy = 2.0 * (w * x + y * z);
    double cy_sq = cxcy * cxcy + sxcy * sxcy;
    if (cy_sq > 1e-20) {
      return wpi::units::radian_t{gcem::atan2(sxcy, cxcy)};
    } else {
      return 0_rad;
    }
  }
 
  /**
   * Returns the counterclockwise rotation angle around the Y axis (pitch).
   */
  constexpr wpi::units::radian_t Y() const {
    double w = m_q.W();
    double x = m_q.X();
    double y = m_q.Y();
    double z = m_q.Z();
 
    // https://en.wikipedia.org/wiki/Conversion_between_quaternions_and_Euler_angles#Quaternion_to_Euler_angles_(in_3-2-1_sequence)_conversion
    double ratio = 2.0 * (w * y - z * x);
    if (gcem::abs(ratio) >= 1.0) {
      return wpi::units::radian_t{
          gcem::copysign(std::numbers::pi / 2.0, ratio)};
    } else {
      return wpi::units::radian_t{gcem::asin(ratio)};
    }
  }
 
  /**
   * Returns the counterclockwise rotation angle around the Z axis (yaw).
   */
  constexpr wpi::units::radian_t Z() const {
    double w = m_q.W();
    double x = m_q.X();
    double y = m_q.Y();
    double z = m_q.Z();
 
    // wpimath/algorithms.md
    double cycz = 1.0 - 2.0 * (y * y + z * z);
    double cysz = 2.0 * (w * z + x * y);
    double cy_sq = cycz * cycz + cysz * cysz;
    if (cy_sq > 1e-20) {
      return wpi::units::radian_t{gcem::atan2(cysz, cycz)};
    } else {
      return wpi::units::radian_t{gcem::atan2(2.0 * w * z, w * w - z * z)};
    }
  }
 
  /**
   * Returns the axis in the axis-angle representation of this rotation.
   */
  constexpr Eigen::Vector3d Axis() const {
    double norm = gcem::hypot(m_q.X(), m_q.Y(), m_q.Z());
    if (norm == 0.0) {
      return Eigen::Vector3d{{0.0, 0.0, 0.0}};
    } else {
      return Eigen::Vector3d{{m_q.X() / norm, m_q.Y() / norm, m_q.Z() / norm}};
    }
  }
 
  /**
   * Returns the angle in the axis-angle representation of this rotation.
   */
  constexpr wpi::units::radian_t Angle() const {
    double norm = gcem::hypot(m_q.X(), m_q.Y(), m_q.Z());
    return wpi::units::radian_t{2.0 * gcem::atan2(norm, m_q.W())};
  }
 
  /**
   * Returns rotation matrix representation of this rotation.
   */
  constexpr Eigen::Matrix3d ToMatrix() const {
    double w = m_q.W();
    double x = m_q.X();
    double y = m_q.Y();
    double z = m_q.Z();
 
    // https://en.wikipedia.org/wiki/Quaternions_and_spatial_rotation#Quaternion-derived_rotation_matrix
    return Eigen::Matrix3d{{1.0 - 2.0 * (y * y + z * z), 2.0 * (x * y - w * z),
                            2.0 * (x * z + w * y)},
                           {2.0 * (x * y + w * z), 1.0 - 2.0 * (x * x + z * z),
                            2.0 * (y * z - w * x)},
                           {2.0 * (x * z - w * y), 2.0 * (y * z + w * x),
                            1.0 - 2.0 * (x * x + y * y)}};
  }
 
  /**
   * Returns rotation vector representation of this rotation.
   *
   * @return Rotation vector representation of this rotation.
   */
  constexpr Eigen::Vector3d ToVector() const { return m_q.ToRotationVector(); }
 
  /**
   * Returns a Rotation2d representing this Rotation3d projected into the X-Y
   * plane.
   */
  constexpr Rotation2d ToRotation2d() const { return Rotation2d{Z()}; }
 
 private:
  Quaternion m_q;
};
 
WPILIB_DLLEXPORT
void to_json(wpi::util::json& json, const Rotation3d& rotation);
 
WPILIB_DLLEXPORT
void from_json(const wpi::util::json& json, Rotation3d& rotation);
 
}  // namespace wpi::math
 
template <>
constexpr wpi::math::Rotation3d wpi::util::Lerp(
    const wpi::math::Rotation3d& startValue,
    const wpi::math::Rotation3d& endValue, double t) {
  return startValue.Interpolate(endValue, t);
}
 
#include "wpi/math/geometry/proto/Rotation3dProto.hpp"
#include "wpi/math/geometry/struct/Rotation3dStruct.hpp"