CovarianceTransport.hpp

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// This file is part of the Acts project.
//
// Copyright (C) 2021 CERN for the benefit of the Acts project
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.

#pragma once

#include "Acts/Definitions/Algebra.hpp"
#include "Acts/Definitions/TrackParametrization.hpp"
#include "Acts/Geometry/GeometryContext.hpp"
#include "Acts/Surfaces/Surface.hpp"

#include <algorithm>
#include <optional>
#include <tuple>
#include <variant>

namespace Acts {

using VariantCovariance = std::variant<BoundSquareMatrix, FreeSquareMatrix>;

using VariantTransportJacobian =
    std::variant<BoundMatrix, BoundToFreeMatrix, FreeToBoundMatrix, FreeMatrix>;

struct CovarianceCache {
  bool applyTransport = false;

  const Surface* atSurface = nullptr;

  Vector3 atPosition = Vector3::Zero();

  VariantCovariance covariance;

  std::optional<BoundToFreeMatrix> boundToFreeJacobian = std::nullopt;
  std::optional<ActsMatrix<8, 7>> anglesToDirectionJacobian = std::nullopt;
  std::optional<ActsMatrix<7, 8>> directionToAnglesJacobian = std::nullopt;

  FreeMatrix freeTransportJacobian = FreeMatrix::Identity();
  FreeVector freeToPathDerivatives = FreeVector::Zero();

  CovarianceCache() = default;

  CovarianceCache(const GeometryContext& gctx, const Surface& surface,
                  const Vector3& position, const BoundVector& boundParameters,
                  const BoundSquareMatrix& boundCovariance);

  CovarianceCache(const Vector3& position, const Vector3& direction,
                  const BoundSquareMatrix& boundCovariance);

  CovarianceCache(const FreeVector& freeParameters,
                  const FreeSquareMatrix& freeCovariance);
};

std::tuple<VariantCovariance, VariantTransportJacobian>
transportCovarianceToBound(const GeometryContext& gctx, const Surface& surface,
                           const FreeVector& parameters,
                           CovarianceCache& cCache);

std::tuple<VariantCovariance, VariantTransportJacobian>
transportCovarianceToCurvilinear(const Vector3& direction,
                                 CovarianceCache& cCache);

std::tuple<VariantCovariance, VariantTransportJacobian>
transportCovarianceToFree(CovarianceCache& cCache);

}  // namespace Acts