ordinate.h

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// SPDX-License-Identifier: BSD-3-Clause
// Copyright (c) 2026, Liam Pohlmann
 
#ifndef HUMMINGBIRD_ORDINATE_H_
#define HUMMINGBIRD_ORDINATE_H_
 
#include <armadillo>
 
namespace hummingbird {
 
/**
 * @brief Defines a solid angle, or *ordinate*, in spherical geometry
 *
 */
class Ordinate {
 public:
  /**
   * @brief Construct a new Ordinate object
   *
   * @param azimuth Azimuthal angle \f$\theta\in [-\pi,\pi]\f$
   * @param polar Polar angle \f$\varphi\in [0,\pi]\f$
   */
  Ordinate(const double azimuth, const double polar);
 
  /**
   * @brief Construct a new Ordinate object in the reflected direction given a
   * starting direction and surface normal vector
   *
   * @param ordinate Initial direction
   * @param surface_normal Surface normal vector
   */
  static Ordinate Reflect(const Ordinate& ordinate,
                          const arma::vec3 surface_normal);
 
  /**
   * @brief Getter for azimuthal angle
   *
   * @return double
   */
  double azimuth() const { return azimuth_; }
 
  /**
   * @brief Getter for polar angle
   *
   * @return double
   */
  double polar() const { return polar_; }
 
  /**
   * @brief Evaluate the x-direction cosine
   *
   * @return double
   */
  double x() const;
 
  /**
   * @brief Evaluate the y-direction cosine
   *
   * @return double
   */
  double y() const;
 
  /**
   * @brief Evaluate the z-direction cosine
   *
   * @return double
   */
  double z() const;
 
  /**
   * @brief Returns the Ordinate as a Cartesian unit vector
   *
   * @return arma::vec3
   */
  arma::vec3 CartesianUnitVector() const;
 
 private:
  /// @brief Azimuthal angle in radians
  const double azimuth_;
 
  /// @brief Polar angle in radians
  const double polar_;
 
  /**
   * @brief Check that input angles are within expected bounds
   *
   * @param azimuth Azimuthal angle in radians
   * @param polar Polar angle in radians
   */
  void CheckInput(const double azimuth, const double polar);
};
}  // namespace hummingbird
 
#endif  // HUMMINGBIRD_ORDINATE_H_