CoordinateSystem.h

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 <wpi/SymbolExports.h>
 
#include "frc/geometry/CoordinateAxis.h"
#include "frc/geometry/Pose3d.h"
#include "frc/geometry/Rotation3d.h"
#include "frc/geometry/Translation3d.h"
 
namespace frc {
 
/**
 * A helper class that converts Pose3d objects between different standard
 * coordinate frames.
 */
class WPILIB_DLLEXPORT CoordinateSystem {
 public:
  /**
   * Constructs a coordinate system with the given cardinal directions for each
   * axis.
   *
   * @param positiveX The cardinal direction of the positive x-axis.
   * @param positiveY The cardinal direction of the positive y-axis.
   * @param positiveZ The cardinal direction of the positive z-axis.
   * @throws std::domain_error if the coordinate system isn't special orthogonal
   */
  constexpr CoordinateSystem(const CoordinateAxis& positiveX,
                             const CoordinateAxis& positiveY,
                             const CoordinateAxis& positiveZ) {
    // Construct a change of basis matrix from the source coordinate system to
    // the NWU coordinate system. Each column vector in the change of basis
    // matrix is one of the old basis vectors mapped to its representation in
    // the new basis.
    Eigen::Matrix3d R{
        {positiveX.m_axis(0), positiveY.m_axis(0), positiveZ.m_axis(0)},
        {positiveX.m_axis(1), positiveY.m_axis(1), positiveZ.m_axis(1)},
        {positiveX.m_axis(2), positiveY.m_axis(2), positiveZ.m_axis(2)}};
 
    // The change of basis matrix should be a pure rotation. The Rotation3d
    // constructor will verify this by checking for special orthogonality.
    m_rotation = Rotation3d{R};
  }
 
  /**
   * Returns an instance of the North-West-Up (NWU) coordinate system.
   *
   * The +X axis is north, the +Y axis is west, and the +Z axis is up.
   */
  constexpr static CoordinateSystem NWU() {
    return CoordinateSystem{CoordinateAxis::N(), CoordinateAxis::W(),
                            CoordinateAxis::U()};
  }
 
  /**
   * Returns an instance of the East-Down-North (EDN) coordinate system.
   *
   * The +X axis is east, the +Y axis is down, and the +Z axis is north.
   */
  constexpr static CoordinateSystem EDN() {
    return CoordinateSystem{CoordinateAxis::E(), CoordinateAxis::D(),
                            CoordinateAxis::N()};
  }
 
  /**
   * Returns an instance of the NED coordinate system.
   *
   * The +X axis is north, the +Y axis is east, and the +Z axis is down.
   */
  constexpr static CoordinateSystem NED() {
    return CoordinateSystem{CoordinateAxis::N(), CoordinateAxis::E(),
                            CoordinateAxis::D()};
  }
 
  /**
   * Converts the given translation from one coordinate system to another.
   *
   * @param translation The translation to convert.
   * @param from The coordinate system the translation starts in.
   * @param to The coordinate system to which to convert.
   * @return The given translation in the desired coordinate system.
   */
  constexpr static Translation3d Convert(const Translation3d& translation,
                                         const CoordinateSystem& from,
                                         const CoordinateSystem& to) {
    // Convert to NWU, then convert to the new coordinate system
    return translation.RotateBy(from.m_rotation).RotateBy(-to.m_rotation);
  }
 
  /**
   * Converts the given rotation from one coordinate system to another.
   *
   * @param rotation The rotation to convert.
   * @param from The coordinate system the rotation starts in.
   * @param to The coordinate system to which to convert.
   * @return The given rotation in the desired coordinate system.
   */
  constexpr static Rotation3d Convert(const Rotation3d& rotation,
                                      const CoordinateSystem& from,
                                      const CoordinateSystem& to) {
    // Convert to NWU, then convert to the new coordinate system
    return rotation.RotateBy(from.m_rotation).RotateBy(-to.m_rotation);
  }
 
  /**
   * Converts the given pose from one coordinate system to another.
   *
   * @param pose The pose to convert.
   * @param from The coordinate system the pose starts in.
   * @param to The coordinate system to which to convert.
   * @return The given pose in the desired coordinate system.
   */
  constexpr static Pose3d Convert(const Pose3d& pose,
                                  const CoordinateSystem& from,
                                  const CoordinateSystem& to) {
    return Pose3d{Convert(pose.Translation(), from, to),
                  Convert(pose.Rotation(), from, to)};
  }
 
  /**
   * Converts the given transform from one coordinate system to another.
   *
   * @param transform The transform to convert.
   * @param from The coordinate system the transform starts in.
   * @param to The coordinate system to which to convert.
   * @return The given transform in the desired coordinate system.
   */
  constexpr static Transform3d Convert(const Transform3d& transform,
                                       const CoordinateSystem& from,
                                       const CoordinateSystem& to) {
    // coordRot is the rotation that converts between the coordinate systems
    // when applied extrinsically. It first converts to NWU, then converts to
    // the new coordinate system.
    const auto coordRot = from.m_rotation.RotateBy(-to.m_rotation);
    // The new rotation is the extrinsic rotation from convert(zero) to
    // convert(transformRot). That is, applying convertedRot extrinsically to
    // convert(zero) produces convert(transformRot). In the below snippet, we
    // use matrix notation, so rotA rotB applies rotA extrinsically to rotB.
    //
    //   convertedRot convert(zero) = convert(transformRot)
    //   convertedRot = convert(transformRot) convert(zero)⁻¹
    //                = (coordRot transformRot) (coordRot zero)⁻¹
    //                = (coordRot transformRot) coordRot⁻¹
    //
    // In code, the equivalent for rotA rotB is rotB.RotateBy(rotA) (note the
    // change in order), and the equivalent for rot⁻¹ is -rot.
    return Transform3d{
        Convert(transform.Translation(), from, to),
        (-coordRot).RotateBy(transform.Rotation().RotateBy(coordRot))};
  }
 
 private:
  // Rotation from this coordinate system to NWU coordinate system when applied
  // extrinsically
  Rotation3d m_rotation;
};
 
}  // namespace frc