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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/EventData/CompositeSpacePoint.hpp" 0013 #include "Acts/Seeding/detail/CompSpacePointAuxiliaries.hpp" 0014 #include "Acts/Utilities/CalibrationContext.hpp" 0015 #include "Acts/Utilities/Logger.hpp" 0016 0017 #include <memory> 0018 #include <vector> 0019 0020 namespace Acts::Experimental::detail { 0021 0022 /// @brief The FastStrawLineFitter fits a straight line to a set of straw measurements 0023 /// The space points passed to the fitter need to be all straw space 0024 /// points and their straw wires need to be approximately parallel to 0025 /// each other. Under this assumption, each straw measurements can be 0026 /// projected onto the plane which is perpendicular to its straw wire 0027 /// and the residual to the k-th straw is written as 0028 /// 0029 /// R_{k} = T_{z,k} * sin \theta - (T_{y,k} - y_{0})* cos \theta - sign_{k} * r_{k} 0030 /// 0031 /// where, \theta and y_{0} are the two line parameters to fit, T_{z,k} and T_{y,k} are 0032 /// the coordinates of the straw-tube in the plane, sign_{k} fixes the 0033 /// left-right ambiguity, and r_{k} is the drift radius of the 0034 /// measurement. The z & y coordinates are given by the dot product of 0035 /// the straw's local position with its planeNormal & toNextSensor 0036 /// vector, respectively. Assuming that the drift radius does not need 0037 /// to be calibrated during the fit, the entire problem reduces to the 0038 /// minimization of a polynomial having the form 0039 /// 0040 /// A * cos(\theta) + B * sin(\theta) + C * cos(2\theta) + D * sin(2\theta) 0041 /// where A, B, C, D are fit constants depending on the configuration of 0042 /// the tubes to fit. They are documented in 0043 /// https://gitlab.cern.ch/atlas-nextgen/work-package-2.5/analyticalsegment 0044 /// 0045 class FastStrawLineFitter { 0046 public: 0047 /// @brief abrivation of the residual indices to fetch the proper covariance 0048 using ResidualIdx = CompSpacePointAuxiliaries::ResidualIdx; 0049 /// @brief Vector type 0050 using Vector = CompSpacePointAuxiliaries::Vector; 0051 /// @brief Configuration object 0052 struct Config { 0053 /// @brief Number of maximum iterations 0054 std::size_t maxIter{10}; 0055 /// @brief Cutoff to def 0056 double precCutOff{1.e-9}; 0057 }; 0058 /// @brief Constructor of the fast straw line fitter 0059 /// @param cfg: Reference to the fitter's configuration object 0060 /// @param logger: Optional overwrite of the logging object 0061 explicit FastStrawLineFitter(const Config& cfg, 0062 std::unique_ptr<const Logger> logger = 0063 getDefaultLogger("FastStrawLineFitter", 0064 Logging::Level::INFO)); 0065 0066 /// @brief Helper struct to pack the result of the straw line fit 0067 struct FitResult { 0068 virtual ~FitResult() = default; 0069 /// @brief Printer method 0070 virtual void print(std::ostream& ostr) const; 0071 /// @brief Ostream operator 0072 friend std::ostream& operator<<(std::ostream& ostr, const FitResult& x) { 0073 x.print(ostr); 0074 return ostr; 0075 } 0076 /// @brief Fitted inclination angle 0077 double theta{0.}; 0078 /// @brief Uncertainty on the fitted angle 0079 double dTheta{0.}; 0080 /// @brief Fitted line intercept 0081 double y0{0.}; 0082 /// @brief Uncertainty on the intercept 0083 double dY0{0.}; 0084 /// @brief Evaluated chi2 postfit 0085 double chi2{0.}; 0086 /// @brief Number of degrees of freedom 0087 std::size_t nDoF{0}; 0088 /// @brief Number of iterations to converge 0089 std::size_t nIter{0}; 0090 }; 0091 0092 /// @brief Brief fit a straight line to a set of straw measurements and return 0093 /// the theta angle & the intercept as well as the associated 0094 /// uncertainties. 0095 /// @param measuremments: Collection of straw measurements to fit 0096 /// @param signs: Convention of whether the straw-line shall be left or right 0097 /// of a particular straw measurements. Needs to have the same 0098 /// length as the list of measurements. 0099 template <CompositeSpacePointContainer StrawCont_t> 0100 std::optional<FitResult> fit(const StrawCont_t& measurements, 0101 const std::vector<int>& signs) const; 0102 0103 private: 0104 /// @brief Index of the drift circle covariance inside the straw 0105 /// space-point's covariance array 0106 static constexpr auto s_covIdx = toUnderlying(ResidualIdx::bending); 0107 0108 ///@brief Auxiliary struct to calculate the fast-fit constants 0109 struct FitAuxiliaries { 0110 /// @brief Default destructor 0111 virtual ~FitAuxiliaries() = default; 0112 /// @brief default constructor 0113 FitAuxiliaries() = default; 0114 /// @brief move constructor 0115 FitAuxiliaries(FitAuxiliaries&& other) = default; 0116 /// @brief Printer method 0117 virtual void print(std::ostream& ostr) const; 0118 /// @brief Ostream operator 0119 friend std::ostream& operator<<(std::ostream& ostr, 0120 const FitAuxiliaries& x) { 0121 x.print(ostr); 0122 return ostr; 0123 } 0124 ///@brief Tube position center - y weighted with inverse covariances 0125 double centerY{0.}; 0126 ///@brief Tube position center - z weighted with inverse covariances 0127 double centerZ{0.}; 0128 /// @brief Inverse covariances per straw measurement 0129 std::vector<double> invCovs{}; 0130 ///@brief One over the sum of the inverse straw measurement covariances 0131 double covNorm{0.}; 0132 ///@brief Expectation value of T_{z}^{2} - T_{y}^{2} 0133 double T_zzyy{0.}; 0134 ///@brief Expectation value of T_{y} * T_{z} 0135 double T_yz{0.}; 0136 ///@brief Expectation value of T_{z} * r 0137 double T_rz{0.}; 0138 ///@brief Expectation value of T_{y} * r 0139 double T_ry{0.}; 0140 ///@brief Prediced y0 given as the expectation value of the radii 0141 /// divided by the inverse covariance sum. 0142 double fitY0{0.}; 0143 /// @brief number of degrees of freedom 0144 std::size_t nDoF{0}; 0145 }; 0146 /// @brief Small Helper struct to calculate sin & cos of theta & 2 theta 0147 struct TrigonomHelper { 0148 /// @brief Constructor passing the theta angle 0149 explicit TrigonomHelper(const double theta) 0150 : cosTheta{std::cos(theta)}, 0151 sinTheta{std::sin(theta)}, 0152 cosTwoTheta{std::cos(2. * theta)}, 0153 sinTwoTheta{std::sin(2. * theta)} {} 0154 double cosTheta{0.}; 0155 double sinTheta{0.}; 0156 double cosTwoTheta{0.}; 0157 double sinTwoTheta{0.}; 0158 }; 0159 /// @brief Calculate the pure angular derivatives of the chi2 w.r.t theta 0160 /// @param angles: Wrapper object to pass sin & cos of theta 0161 /// @param fitPars: Constants of the current fit configuration 0162 /// @param thetaPrime: Mutable reference to which the first derivative is written 0163 /// @param thetaTwoPrime: Mutable reference to which the second derivative is written 0164 void calcAngularDerivatives(const TrigonomHelper& angles, 0165 const FitAuxiliaries& fitPars, double& thetaPrime, 0166 double& thetaTwoPrime) const; 0167 /// @brief Calculate the fit constants for a set of straw circles 0168 /// @param measurements: List of straw measurements 0169 /// @param signs: List of left/right signs to be annotated with each straw circle 0170 template <CompositeSpacePointContainer StrawCont_t> 0171 FitAuxiliaries fillAuxiliaries(const StrawCont_t& measurements, 0172 const std::vector<int>& signs) const; 0173 /// @brief Evaluate the chi2 after the fit has converged. 0174 /// @param measurements: List of straw measurements that have been used in the fit 0175 /// @param result: Mutable reference to the FitResult object. The object is used 0176 /// to fetch the fit parameters and to store the chi2 result 0177 template <CompositeSpacePointContainer StrawCont_t> 0178 void calcPostFitChi2(const StrawCont_t& measurements, 0179 FitResult& result) const; 0180 /// @brief Calculate the chi2 term from a straw measurement given the known theta, y0 0181 /// @param angle: Helper struct caching the cosTheta & sinTheta 0182 /// @param y0: Intercept of the fitted line 0183 /// @param strawMeas: Reference to the straw measurement of interest 0184 /// @param r: Optional updated calibrated straw radius 0185 template <CompositeSpacePoint Point_t> 0186 double chi2Term(const TrigonomHelper& angle, const double y0, 0187 const Point_t& strawMeas, 0188 std::optional<double> r = std::nullopt) const; 0189 /// @brief Fit the track inclination angle and calculate the intercept 0190 /// afterwards 0191 /// @param fitPars: Constants of the current measurement configuration 0192 std::optional<FitResult> fit(const FitAuxiliaries& fitPars) const; 0193 /// @brief Calculate the starting parameters on theta from the fit constants 0194 static double startTheta(const FitAuxiliaries& fitPars); 0195 /// @brief Fill the y0 and the uncertainties on theta and y0 in the result 0196 /// @param fitPars: Fit constants from the straw measurements 0197 /// @param thetaTwoPrime: Second derivative of the chi2 w.r.t theta 0198 /// @param result: Mutable reference to the FitResult object. The updated parameter are written 0199 /// to this object 0200 void completeResult(const FitAuxiliaries& fitPars, const double thetaTwoPrime, 0201 FitResult& result) const; 0202 0203 const Config m_cfg{}; 0204 std::unique_ptr<const Acts::Logger> m_logger{}; 0205 0206 const Acts::Logger& logger() const; 0207 }; 0208 0209 } // namespace Acts::Experimental::detail 0210 #include "Acts/Seeding/detail/FastStrawLineFitter.ipp"
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