generalized_absolute_pose.h

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// ----------------------------------------------------------------------------
// -                        CloudViewer: www.cloudViewer.org                  -
// ----------------------------------------------------------------------------
// Copyright (c) 2018-2024 www.cloudViewer.org
// SPDX-License-Identifier: MIT
// ----------------------------------------------------------------------------
 
#pragma once
 
#include <Eigen/Core>
#include <vector>
 
#include "util/alignment.h"
#include "util/types.h"
 
namespace colmap {
 
// Solver for the Generalized P3P problem (NP3P or GP3P), based on:
//
//      Lee, Gim Hee, et al. "Minimal solutions for pose estimation of a
//      multi-camera system." Robotics Research. Springer International
//      Publishing, 2016. 521-538.
//
// This class is based on an original implementation by Federico Camposeco.
class GP3PEstimator {
public:
    // The generalized image observations, which is composed of the relative
    // pose of the specific camera in the generalized camera and its image
    // observation.
    struct X_t {
        // The relative transformation from the generalized camera to the camera
        // frame of the observation.
        Eigen::Matrix3x4d rel_tform;
        // The 2D image feature observation.
        Eigen::Vector2d xy;
    };
 
    // The observed 3D feature points in the world frame.
    typedef Eigen::Vector3d Y_t;
    // The transformation from the world to the generalized camera frame.
    typedef Eigen::Matrix3x4d M_t;
 
    // The minimum number of samples needed to estimate a model.
    static const int kMinNumSamples = 3;
 
    enum class ResidualType {
        CosineDistance,
        ReprojectionError,
    };
 
    // Whether to compute the cosine similarity or the reprojection error.
    // [WARNING] The reprojection error being in normalized coordinates,
    // the unique error threshold of RANSAC corresponds to different pixel
    // values in the different cameras of the rig if they have different
    // intrinsics.
    ResidualType residual_type = ResidualType::CosineDistance;
 
    // Estimate the most probable solution of the GP3P problem from a set of
    // three 2D-3D point correspondences.
    static std::vector<M_t> Estimate(const std::vector<X_t>& points2D,
                                     const std::vector<Y_t>& points3D);
 
    // Calculate the squared cosine distance error between the rays given a set
    // of 2D-3D point correspondences and a projection matrix of the generalized
    // camera.
    void Residuals(const std::vector<X_t>& points2D,
                   const std::vector<Y_t>& points3D,
                   const M_t& proj_matrix,
                   std::vector<double>* residuals);
};
 
}  // namespace colmap
 
// EIGEN_DEFINE_STL_VECTOR_SPECIALIZATION_CUSTOM(colmap::GP3PEstimator::X_t)