Class Acts::SingleBoundTrackParameters

template<class charge_t>
class Acts::SingleBoundTrackParameters

Track parameters bound to a reference surface for a single track.

This is intended as a user-facing data class that adds additional accessors and charge/momentum interpretation on top of the pure parameters vector. All parameters and their corresponding covariance matrix are stored in bound parametrization. The specific definition of the local spatial parameters is defined by the associated surface.

tparam charge_t

Helper type to interpret the particle charge/momentum

Note

This class holds shared ownership on its reference surface.

Subclassed by Acts::SingleCurvilinearTrackParameters< charge_t >

Public Types

using CovarianceMatrix = BoundSymMatrix
using ParametersVector = BoundVector
using Scalar = ActsScalar

Public Functions

inline SingleBoundTrackParameters(std::shared_ptr<const Surface> surface, const ParametersVector &params, Scalar q, std::optional<CovarianceMatrix> cov = std::nullopt)

Construct from a parameters vector on the surface and particle charge.

In principle, only the charge magnitude is needed her to allow unambigous extraction of the absolute momentum. The particle charge is required as an input here to be consistent with the other constructors below that that also take the charge as an input. The charge sign is only used in debug builds to check for consistency with the q/p parameter.

Parameters
  • surface – Reference surface the parameters are defined on

  • params – Bound parameters vector

  • q – Particle charge

  • cov – Bound parameters covariance matrix

template<typename T = charge_t, std::enable_if_t<std::is_default_constructible_v<T>, int> = 0>
inline SingleBoundTrackParameters(std::shared_ptr<const Surface> surface, const ParametersVector &params, std::optional<CovarianceMatrix> cov = std::nullopt)

Construct from a parameters vector on the surface.

This constructor is only available if there are no potential charge ambiguities, i.e. the charge type is default-constructible.

Parameters
  • surface – Reference surface the parameters are defined on

  • params – Bound parameters vector

  • cov – Bound parameters covariance matrix

SingleBoundTrackParameters() = delete

Parameters are not default constructible due to the charge type.

SingleBoundTrackParameters(const SingleBoundTrackParameters&) = default
SingleBoundTrackParameters(SingleBoundTrackParameters&&) = default
~SingleBoundTrackParameters() = default
inline Scalar absoluteMomentum() const

Absolute momentum.

inline Scalar charge() const

Particle electric charge.

inline const std::optional<CovarianceMatrix> &covariance() const

Optional covariance matrix.

inline Vector4 fourPosition(const GeometryContext &geoCtx) const

Space-time position four-vector.

This uses the associated surface to transform the local position on the surface to globalcoordinates. This requires a geometry context to select the appropriate transformation and might be a computationally expensive operation.

Parameters

geoCtx[in] Geometry context for the local-to-global transformation

template<BoundIndices kIndex>
inline Scalar get() const

Access a single parameter value indentified by its index.

Template Parameters

kIndex – Track parameter index

inline Vector3 momentum() const

Momentum three-vector.

SingleBoundTrackParameters &operator=(const SingleBoundTrackParameters&) = default
SingleBoundTrackParameters &operator=(SingleBoundTrackParameters&&) = default
inline const ParametersVector &parameters() const

Parameters vector.

inline Vector3 position(const GeometryContext &geoCtx) const

Spatial position three-vector.

This uses the associated surface to transform the local position on the surface to globalcoordinates. This requires a geometry context to select the appropriate transformation and might be a computationally expensive operation.

Parameters

geoCtx[in] Geometry context for the local-to-global transformation

inline RotationMatrix3 referenceFrame(const GeometryContext &geoCtx) const

Reference frame in which the local error is defined.

For planar surfaces, this is the transformation local-to-global rotation matrix. For non-planar surfaces, it is the local-to-global rotation matrix of the tangential plane at the track position.

Parameters

geoCtx[in] Geometry context for the local-to-global transformation

inline const Surface &referenceSurface() const

Reference surface onto which the parameters are bound.

inline Scalar time() const

Time coordinate.

inline Scalar transverseMomentum() const

Transverse momentum.

inline Vector3 unitDirection() const

Unit direction three-vector, i.e.

the normalized momentum three-vector.

Public Static Functions

static inline Result<SingleBoundTrackParameters<charge_t>> create(std::shared_ptr<const Surface> surface, const GeometryContext &geoCtx, const Vector4 &pos4, const Vector3 &dir, Scalar p, Scalar q, std::optional<CovarianceMatrix> cov = std::nullopt)

Factory to construct from four-position, direction, absolute momentum, and charge.

Note

The returned result indicates whether the free parameters could successfully be converted to on-surface parameters.

Parameters
  • surface – Reference surface the parameters are defined on

  • geoCtx – Geometry context for the local-to-global transformation

  • pos4 – Track position/time four-vector

  • dir – Track direction three-vector; normalization is ignored.

  • p – Absolute momentum

  • q – Particle charge

  • cov – Bound parameters covariance matrix

template<typename T = charge_t, std::enable_if_t<std::is_default_constructible_v<T>, int> = 0>
static inline Result<SingleBoundTrackParameters<charge_t>> create(std::shared_ptr<const Surface> surface, const GeometryContext &geoCtx, const Vector4 &pos4, const Vector3 &dir, Scalar qOverP, std::optional<CovarianceMatrix> cov = std::nullopt)

Factory to construct from four-position, direction, and charge-over-momentum.

Note

This factory is only available if there are no potential charge ambiguities, i.e. the charge type is default-constructible. The position must be located on the surface.

Note

The returned result indicates whether the free parameters could successfully be converted to on-surface parameters.

Parameters
  • surface – Reference surface the parameters are defined on

  • geoCtx – Geometry context for the local-to-global transformation

  • pos4 – Track position/time four-vector

  • dir – Track direction three-vector; normalization is ignored.

  • qOverP – Charge-over-momentum-like parameter

  • cov – Bound parameters covariance matrix