Function SquaredSphericalReprojectionError

src/colmap/scene/projection.cc:46–52

Pixel reprojection error is ill-defined for equirectangular (e.g. EQUIRECTANGULAR) cameras: the azimuth is discontinuous at the ±π seam and its pixel scale diverges towards the poles (azimuth pixels grow as 1/cos(elevation)). Instead measure the angular error between the observed bearing and the 3D point and convert it to an equivalent pixel error at the equator, consistent with the model's pixel<

// CamFromImgThreshold. This makes the (squared) error continuous across the
// seam and uniform over the sphere.
double SquaredSphericalReprojectionError(const double angular_error,
                                         const Camera& camera) {
  const double pixels_per_radian =
      static_cast<double>(camera.width) / (2.0 * EIGEN_PI);
  const double pixel_error = angular_error * pixels_per_radian;
  return pixel_error * pixel_error;
}

}  // namespace