translation_transform.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 <Eigen/Geometry>
#include <vector>
 
#include "util/alignment.h"
#include "util/logging.h"
#include "util/types.h"
 
namespace colmap {
 
// Estimate a N-D translation transformation between point pairs.
template <int kDim>
class TranslationTransformEstimator {
public:
    typedef Eigen::Matrix<double, kDim, 1> X_t;
    typedef Eigen::Matrix<double, kDim, 1> Y_t;
    typedef Eigen::Matrix<double, kDim, 1> M_t;
 
    // The minimum number of samples needed to estimate a model.
    static const int kMinNumSamples = 1;
 
    // Estimate the 2D translation transform.
    //
    // @param points1      Set of corresponding source 2D points.
    // @param points2      Set of corresponding destination 2D points.
    //
    // @return             Translation vector.
    static std::vector<M_t> Estimate(const std::vector<X_t>& points1,
                                     const std::vector<Y_t>& points2);
 
    // Calculate the squared translation error.
    //
    // @param points1      Set of corresponding source 2D points.
    // @param points2      Set of corresponding destination 2D points.
    // @param translation  Translation vector.
    // @param residuals    Output vector of residuals for each point pair.
    static void Residuals(const std::vector<X_t>& points1,
                          const std::vector<Y_t>& points2,
                          const M_t& translation,
                          std::vector<double>* residuals);
};
 
// Implementation
 
template <int kDim>
std::vector<typename TranslationTransformEstimator<kDim>::M_t>
TranslationTransformEstimator<kDim>::Estimate(const std::vector<X_t>& points1,
                                              const std::vector<Y_t>& points2) {
    CHECK_EQ(points1.size(), points2.size());
 
    X_t mean_src = X_t::Zero();
    Y_t mean_dst = Y_t::Zero();
 
    for (size_t i = 0; i < points1.size(); ++i) {
        mean_src += points1[i];
        mean_dst += points2[i];
    }
 
    mean_src /= points1.size();
    mean_dst /= points2.size();
 
    std::vector<M_t> models(1);
    models[0] = mean_dst - mean_src;
 
    return models;
}
 
template <int kDim>
void TranslationTransformEstimator<kDim>::Residuals(
        const std::vector<X_t>& points1,
        const std::vector<Y_t>& points2,
        const M_t& translation,
        std::vector<double>* residuals) {
    CHECK_EQ(points1.size(), points2.size());
 
    residuals->resize(points1.size());
 
    for (size_t i = 0; i < points1.size(); ++i) {
        const M_t diff = points2[i] - points1[i] - translation;
        (*residuals)[i] = diff.squaredNorm();
    }
}
 
}  // namespace colmap