// Copyright (c), ETH Zurich and UNC Chapel Hill.
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//
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//
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//       notice, this list of conditions and the following disclaimer.
//
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//
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//       its contributors may be used to endorse or promote products derived
//       from this software without specific prior written permission.
//
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#pragma once

#include "colmap/geometry/rigid3.h"
#include "colmap/util/eigen_alignment.h"

#include <vector>

#include <Eigen/Core>

namespace colmap {

struct GRNPObservation {
  Rigid3d cam_from_rig;
  Eigen::Vector3d ray_in_cam;
};

// Minimal generalized relative pose estimator based on poselib.
class GR6PEstimator {
 public:
  using X_t = GRNPObservation;
  using Y_t = GRNPObservation;
  // The estimated rig2_from_rig1 relative pose between the generalized cameras.
  using M_t = Rigid3d;

  // The minimum number of samples needed to estimate a model. Note that in
  // theory the minimum required number of samples is 6 but Laurent Kneip showed
  // in his paper that using 8 samples is more stable.
  static const int kMinNumSamples = 6;

  // Estimate the most probable solution of the GR6P problem from a set of
  // six 2D-2D point correspondences.
  static void Estimate(const std::vector<X_t>& points1,
                       const std::vector<Y_t>& points2,
                       std::vector<M_t>* rigs2_from_rigs1);

  // Calculate the squared Sampson error between corresponding points.
  static void Residuals(const std::vector<X_t>& points1,
                        const std::vector<Y_t>& points2,
                        const M_t& rig2_from_rig1,
                        std::vector<double>* residuals);
};

// Solver for the Generalized Relative Pose problem using a minimal of 8 2D-2D
// correspondences. This implementation is based on:
//
//    "Efficient Computation of Relative Pose for Multi-Camera Systems",
//    Kneip and Li. CVPR 2014.
//
// Note that the solution to this problem is degenerate in the case of pure
// translation and when all correspondences are observed from the same cameras.
//
// The implementation is a modified and improved version of Kneip's original
// implementation in OpenGV licensed under the BSD license.
class GR8PEstimator {
 public:
  using X_t = GRNPObservation;
  using Y_t = GRNPObservation;
  // The estimated rig2_from_rig1 relative pose between the generalized cameras.
  using M_t = Rigid3d;

  // The minimum number of samples needed to estimate a model. Note that in
  // theory the minimum required number of samples is 6 but Laurent Kneip showed
  // in his paper that using 8 samples is more stable.
  static const int kMinNumSamples = 8;

  // Estimate the most probable solution of the GR8P problem from a set of
  // eight 2D-2D point correspondences.
  static void Estimate(const std::vector<X_t>& points1,
                       const std::vector<Y_t>& points2,
                       std::vector<M_t>* rigs2_from_rigs1);

  // Calculate the squared Sampson error between corresponding points.
  static void Residuals(const std::vector<X_t>& points1,
                        const std::vector<Y_t>& points2,
                        const M_t& rig2_from_rig1,
                        std::vector<double>* residuals);
};

}  // namespace colmap
