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piecewise_quaternion.cc
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piecewise_quaternion.cc
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#include "drake/common/trajectories/piecewise_quaternion.h"
#include <algorithm>
#include <stdexcept>
#include "drake/common/trajectories/piecewise_polynomial.h"
#include "drake/math/quaternion.h"
namespace drake {
namespace trajectories {
using std::abs;
using std::cos;
using std::max;
using std::min;
template <typename T>
bool PiecewiseQuaternionSlerp<T>::is_approx(
const PiecewiseQuaternionSlerp<T>& other, double tol) const {
// Velocities are derived from the quaternions, and I don't want to
// overload units for tol, so I am skipping the checks on velocities.
if (!this->SegmentTimesEqual(other, tol))
return false;
if (quaternions_.size() != other.quaternions_.size())
return false;
for (size_t i = 0; i < quaternions_.size(); ++i) {
// A quick reference:
// Page "Metric on sphere of unit quaternions" from
// http://www.cs.cmu.edu/afs/cs/academic/class/16741-s07/www/Lecture8.pdf
double dot =
abs(ExtractDoubleOrThrow(quaternions_[i].dot(other.quaternions_[i])));
if (dot < cos(tol / 2)) {
return false;
}
}
return true;
}
namespace internal {
template <typename T>
Vector3<T> ComputeAngularVelocity(const T& duration, const Quaternion<T>& q,
const Quaternion<T>& qnext) {
// Computes qnext = q_delta * q first, turn q_delta into an axis, which
// turns into an angular velocity.
AngleAxis<T> angle_axis_diff(qnext * q.inverse());
return angle_axis_diff.axis() * angle_axis_diff.angle() / duration;
}
} // namespace internal
template <typename T>
void PiecewiseQuaternionSlerp<T>::Initialize(
const std::vector<T>& breaks,
const std::vector<Quaternion<T>>& quaternions) {
if (quaternions.size() != breaks.size()) {
throw std::logic_error("Quaternions and breaks length mismatch.");
}
if (quaternions.size() < 2) {
throw std::logic_error("Not enough quaternions for slerp.");
}
quaternions_.resize(breaks.size());
angular_velocities_.resize(breaks.size() - 1);
// Set to the closest wrt to the previous, also normalize.
for (size_t i = 0; i < quaternions.size(); ++i) {
if (i == 0) {
quaternions_[i] = quaternions[i].normalized();
} else {
quaternions_[i] =
math::ClosestQuaternion(quaternions_[i - 1], quaternions[i]);
angular_velocities_[i - 1] = internal::ComputeAngularVelocity(
this->duration(i - 1), quaternions_[i - 1], quaternions[i]);
}
}
}
template <typename T>
PiecewiseQuaternionSlerp<T>::PiecewiseQuaternionSlerp(
const std::vector<T>& breaks,
const std::vector<Quaternion<T>>& quaternions)
: PiecewiseTrajectory<T>(breaks) {
Initialize(breaks, quaternions);
}
template <typename T>
PiecewiseQuaternionSlerp<T>::PiecewiseQuaternionSlerp(
const std::vector<T>& breaks,
const std::vector<Matrix3<T>>& rot_matrices)
: PiecewiseTrajectory<T>(breaks) {
std::vector<Quaternion<T>> quaternions(rot_matrices.size());
for (size_t i = 0; i < rot_matrices.size(); ++i) {
quaternions[i] = Quaternion<T>(rot_matrices[i]);
}
Initialize(breaks, quaternions);
}
template <typename T>
PiecewiseQuaternionSlerp<T>::PiecewiseQuaternionSlerp(
const std::vector<T>& breaks,
const std::vector<math::RotationMatrix<T>>& rot_matrices)
: PiecewiseTrajectory<T>(breaks) {
std::vector<Quaternion<T>> quaternions(rot_matrices.size());
for (size_t i = 0; i < rot_matrices.size(); ++i) {
quaternions[i] = rot_matrices[i].ToQuaternion();
}
Initialize(breaks, quaternions);
}
template <typename T>
PiecewiseQuaternionSlerp<T>::PiecewiseQuaternionSlerp(
const std::vector<T>& breaks,
const std::vector<AngleAxis<T>>& ang_axes)
: PiecewiseTrajectory<T>(breaks) {
std::vector<Quaternion<T>> quaternions(ang_axes.size());
for (size_t i = 0; i < ang_axes.size(); ++i) {
quaternions[i] = Quaternion<T>(ang_axes[i]);
}
Initialize(breaks, quaternions);
}
template <typename T>
std::unique_ptr<Trajectory<T>> PiecewiseQuaternionSlerp<T>::Clone() const {
return std::make_unique<PiecewiseQuaternionSlerp>(*this);
}
template <typename T>
T PiecewiseQuaternionSlerp<T>::ComputeInterpTime(int segment_index,
const T& time) const {
T interp_time =
(time - this->start_time(segment_index)) / this->duration(segment_index);
interp_time = max(interp_time, T(0.0));
interp_time = min(interp_time, T(1.0));
return interp_time;
}
template <typename T>
Quaternion<T> PiecewiseQuaternionSlerp<T>::orientation(const T& t) const {
int segment_index = this->get_segment_index(t);
T interp_t = ComputeInterpTime(segment_index, t);
Quaternion<T> q1 = quaternions_.at(segment_index)
.slerp(interp_t, quaternions_.at(segment_index + 1));
q1.normalize();
return q1;
}
template <typename T>
Vector3<T> PiecewiseQuaternionSlerp<T>::angular_velocity(const T& t) const {
int segment_index = this->get_segment_index(t);
return angular_velocities_.at(segment_index);
}
template <typename T>
Vector3<T> PiecewiseQuaternionSlerp<T>::angular_acceleration(const T&) const {
return Vector3<T>::Zero();
}
template <typename T>
void PiecewiseQuaternionSlerp<T>::Append(
const T& time, const Quaternion<T>& quaternion) {
DRAKE_DEMAND(this->breaks().empty() || time > this->breaks().back());
if (quaternions_.empty()) {
quaternions_.push_back(quaternion.normalized());
} else {
angular_velocities_.push_back(internal::ComputeAngularVelocity(
time - this->breaks().back(), quaternions_.back(), quaternion));
quaternions_.push_back(math::ClosestQuaternion(
quaternions_.back(), quaternion));
}
this->get_mutable_breaks().push_back(time);
}
template <typename T>
void PiecewiseQuaternionSlerp<T>::Append(
const T& time, const math::RotationMatrix<T>& rotation_matrix) {
Append(time, rotation_matrix.ToQuaternion());
}
template <typename T>
void PiecewiseQuaternionSlerp<T>::Append(
const T& time, const AngleAxis<T>& angle_axis) {
Append(time, Quaternion<T>(angle_axis));
}
template <typename T>
bool PiecewiseQuaternionSlerp<T>::do_has_derivative() const {
return true;
}
template <typename T>
MatrixX<T> PiecewiseQuaternionSlerp<T>::DoEvalDerivative(
const T& t, int derivative_order) const {
if (derivative_order == 0) {
return value(t);
} else if (derivative_order == 1) {
return angular_velocity(t);
}
// All higher derivatives are zero.
return Vector3<T>::Zero();
}
template <typename T>
std::unique_ptr<Trajectory<T>> PiecewiseQuaternionSlerp<T>::DoMakeDerivative(
int derivative_order) const {
if (derivative_order == 0) {
return this->Clone();
} else if (derivative_order == 1) {
std::vector<MatrixX<T>> m(angular_velocities_.begin(),
angular_velocities_.end());
m.push_back(Vector3<T>::Zero());
return PiecewisePolynomial<T>::ZeroOrderHold(
this->get_segment_times(), m).Clone();
}
// All higher derivatives are zero.
return std::make_unique<PiecewisePolynomial<T>>(Vector3<T>::Zero());
}
} // namespace trajectories
} // namespace drake
DRAKE_DEFINE_CLASS_TEMPLATE_INSTANTIATIONS_ON_DEFAULT_SCALARS(
class drake::trajectories::PiecewiseQuaternionSlerp)