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0001 // This file is part of the ACTS project. 0002 // 0003 // Copyright (C) 2016 CERN for the benefit of the ACTS project 0004 // 0005 // This Source Code Form is subject to the terms of the Mozilla Public 0006 // License, v. 2.0. If a copy of the MPL was not distributed with this 0007 // file, You can obtain one at https://mozilla.org/MPL/2.0/. 0008 0009 #pragma once 0010 0011 #include "Acts/Definitions/Algebra.hpp" 0012 #include "Acts/Definitions/TrackParametrization.hpp" 0013 #include "Acts/Definitions/Units.hpp" 0014 #include "Acts/Geometry/GeometryContext.hpp" 0015 #include "Acts/Seeding/TrackParamsEstimationError.hpp" 0016 #include "Acts/Surfaces/Surface.hpp" 0017 #include "Acts/Utilities/Result.hpp" 0018 0019 #include <cstddef> 0020 #include <span> 0021 0022 namespace Acts { 0023 0024 /// @defgroup est_track_params Estimate track parameters from seed 0025 /// 0026 /// The implemented method is based on the conformal map transformation. It 0027 /// estimates the full free track parameters, i.e. (x, y, z, t, dx, dy, dz, q/p) 0028 /// at the bottom space point. The magnetic field (which can be along any 0029 /// direction) is also necessary for the momentum estimation. 0030 /// 0031 /// It resembles the method used in ATLAS for the track parameters estimated 0032 /// from seed, i.e. the function InDet::SiTrackMaker_xk::getAtaPlane here: 0033 /// https://acode-browser.usatlas.bnl.gov/lxr/source/athena/InnerGeometry/InDetRecTools/SiTrackMakerTool_xk/src/SiTrackMaker_xk.cxx 0034 /// 0035 /// @{ 0036 0037 /// Estimate free track parameters from three space points. 0038 /// 0039 /// Optionally estimates the tangents at the three space points from helix fit. 0040 /// This can be used as an input for the strip space point calibration, which 0041 /// requires the track tangents at each space point as input. 0042 /// 0043 /// @param sp0 is the bottom space point 0044 /// @param t0 is the time of the bottom space point 0045 /// @param sp1 is the middle space point 0046 /// @param sp2 is the top space point 0047 /// @param bField is the magnetic field vector 0048 /// @param tangent0 is the output tangent at the bottom space point 0049 /// @param tangent1 is the output tangent at the middle space point 0050 /// @param tangent2 is the output tangent at the top space point 0051 /// 0052 /// @return the free parameters 0053 FreeVector estimateTrackParamsFromSeed(const Vector3& sp0, double t0, 0054 const Vector3& sp1, const Vector3& sp2, 0055 const Vector3& bField, 0056 Vector3* tangent0 = nullptr, 0057 Vector3* tangent1 = nullptr, 0058 Vector3* tangent2 = nullptr); 0059 0060 /// Estimate bound track parameters from three space points 0061 /// 0062 /// @param gctx is the geometry context 0063 /// @param surface is the surface of the bottom space point. The estimated bound 0064 /// track parameters will be represented at this surface. 0065 /// @param sp0 is the bottom space point 0066 /// @param t0 is the time of the bottom space point 0067 /// @param sp1 is the middle space point 0068 /// @param sp2 is the top space point 0069 /// @param bField is the magnetic field vector 0070 /// 0071 /// @return bound parameters 0072 Result<BoundVector> estimateTrackParamsFromSeed( 0073 const GeometryContext& gctx, const Surface& surface, const Vector3& sp0, 0074 double t0, const Vector3& sp1, const Vector3& sp2, const Vector3& bField); 0075 0076 /// Configuration for the estimation of the covariance matrix of the track 0077 /// parameters with `estimateTrackParamCovariance`. 0078 struct EstimateTrackParamCovarianceConfig { 0079 /// The initial sigmas for the track parameters 0080 BoundVector initialSigmas = {1. * UnitConstants::mm, 0081 1. * UnitConstants::mm, 0082 1. * UnitConstants::degree, 0083 1. * UnitConstants::degree, 0084 1. * UnitConstants::e / UnitConstants::GeV, 0085 1. * UnitConstants::ns}; 0086 0087 /// The initial sigma for the q/pt 0088 /// @note The resulting q/p sigma is added to the one in `initialSigmas` 0089 double initialSigmaQoverPt = 0. * UnitConstants::e / UnitConstants::GeV; 0090 0091 /// The initial relative uncertainty sigma(pt)/pt 0092 /// @note The resulting q/p sigma is added to the one in `initialSigmas` 0093 double initialSigmaPtRel = 0.1; 0094 0095 /// The inflation factors for the variances of the track parameters 0096 BoundVector initialVarInflation = {1., 1., 1., 1., 1., 1.}; 0097 /// The inflation factor for time uncertainty if the time parameter was not 0098 /// estimated 0099 double noTimeVarInflation = 100.; 0100 }; 0101 0102 /// Estimate the covariance matrix of the given track parameters based on the 0103 /// provided configuration. The assumption is that we can model the uncertainty 0104 /// of the track parameters as a diagonal matrix with the provided initial 0105 /// sigmas. The inflation factors are used to inflate the initial variances 0106 /// based on the provided configuration. The uncertainty of q/p is estimated 0107 /// based on the relative uncertainty of the q/pt and the theta uncertainty. 0108 /// 0109 /// @param config is the configuration for the estimation 0110 /// @param params is the track parameters 0111 /// @param hasTime is true if the track parameters have time 0112 /// 0113 /// @return the covariance matrix of the track parameters 0114 BoundMatrix estimateTrackParamCovariance( 0115 const EstimateTrackParamCovarianceConfig& config, const BoundVector& params, 0116 bool hasTime); 0117 0118 /// Estimate free track parameters from an ordered set of N >= 3 space points. 0119 /// 0120 /// Least-squares generalization of @ref estimateTrackParamsFromSeed. A Taubin 0121 /// circle fit transverse to the field, optionally refined geometrically, and a 0122 /// linear fit of the field coordinate against the transverse arc length. Points 0123 /// are taken in track order and are not sorted. 0124 /// 0125 /// The parameters are expressed at `spacePoints[referenceIndex]`, by default 0126 /// the first one. The fit itself does not depend on that choice: every point 0127 /// contributes to the same helix, and the reference only selects where it is 0128 /// evaluated. Reporting at a point deeper in the detector lets a downstream 0129 /// track finder start where the hit density, and with it the combinatorics, is 0130 /// lower, at the cost of a longer extrapolation back to the beam line. 0131 /// 0132 /// A vanishing curvature degenerates to a line and only the direction is 0133 /// estimated. Without a field q/p stays zero. 0134 /// 0135 /// Weights are relative (e.g. inverse-variance) factors on every fit stage. An 0136 /// empty span means uniform, a non-empty one must match `spacePoints` in size. 0137 /// 0138 /// @param spacePoints the ordered global space point positions 0139 /// @param bField the homogeneous magnetic field vector 0140 /// @param t0 the time assigned to the reference point (eFreeTime) 0141 /// @param geometricRefineIterations number of Gauss-Newton refinement 0142 /// iterations on top of the algebraic circle fit (0 disables it) 0143 /// @param weights optional per-point weights for all fit stages 0144 /// (empty span = uniform) 0145 /// @param referenceIndex index of the space point the parameters are expressed 0146 /// at; must be a valid index into `spacePoints` 0147 /// @return the free parameters at the reference point, or an error 0148 Result<FreeVector> estimateTrackParamsFromSpacePoints( 0149 std::span<const Vector3> spacePoints, const Vector3& bField, double t0 = 0, 0150 std::size_t geometricRefineIterations = 0, 0151 std::span<const double> weights = {}, std::size_t referenceIndex = 0); 0152 0153 /// @} 0154 0155 } // namespace Acts
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