conditioning.cc

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// Copyright (c) 2010 libmv authors.
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#include "libmv/multiview/conditioning.h"
#include "libmv/multiview/projection.h"
 
namespace libmv {
 
// HZ 4.4.4 pag.109: Point conditioning (non isotropic)
void PreconditionerFromPoints(const Mat& points, Mat3* T) {
  Vec mean, variance;
  MeanAndVarianceAlongRows(points, &mean, &variance);
 
  double xfactor = sqrt(2.0 / variance(0));
  double yfactor = sqrt(2.0 / variance(1));
 
  // If variance is equal to 0.0 set scaling factor to identity.
  // -> Else it will provide nan value (because division by 0).
  if (variance(0) < 1e-8) {
    xfactor = mean(0) = 1.0;
  }
  if (variance(1) < 1e-8) {
    yfactor = mean(1) = 1.0;
  }
 
  // clang-format off
  *T << xfactor, 0,       -xfactor * mean(0),
        0,       yfactor, -yfactor * mean(1),
        0,       0,        1;
  // clang-format on
}
// HZ 4.4.4 pag.107: Point conditioning (isotropic)
void IsotropicPreconditionerFromPoints(const Mat& points, Mat3* T) {
  Vec mean, variance;
  MeanAndVarianceAlongRows(points, &mean, &variance);
 
  double var_norm = variance.norm();
  double factor = sqrt(2.0 / var_norm);
 
  // If variance is equal to 0.0 set scaling factor to identity.
  // -> Else it will provide nan value (because division by 0).
  if (var_norm < 1e-8) {
    factor = 1.0;
    mean.setOnes();
  }
 
  // clang-format off
  *T << factor, 0,       -factor * mean(0),
        0,       factor, -factor * mean(1),
        0,       0,        1;
  // clang-format on
}
 
void ApplyTransformationToPoints(const Mat& points,
                                 const Mat3& T,
                                 Mat* transformed_points) {
  int n = points.cols();
  transformed_points->resize(2, n);
  Mat3X p(3, n);
  EuclideanToHomogeneous(points, &p);
  p = T * p;
  HomogeneousToEuclidean(p, transformed_points);
}
 
void NormalizePoints(const Mat& points, Mat* normalized_points, Mat3* T) {
  PreconditionerFromPoints(points, T);
  ApplyTransformationToPoints(points, *T, normalized_points);
}
 
void NormalizeIsotropicPoints(const Mat& points,
                              Mat* normalized_points,
                              Mat3* T) {
  IsotropicPreconditionerFromPoints(points, T);
  ApplyTransformationToPoints(points, *T, normalized_points);
}
 
// Denormalize the results. See HZ page 109.
void UnnormalizerT::Unnormalize(const Mat3& T1, const Mat3& T2, Mat3* H) {
  *H = T2.transpose() * (*H) * T1;
}
 
void UnnormalizerI::Unnormalize(const Mat3& T1, const Mat3& T2, Mat3* H) {
  *H = T2.inverse() * (*H) * T1;
}
 
}  // namespace libmv