refactor!: Remove free parameter estimation function

Core/include/Acts/Seeding/EstimateTrackParamsFromSeed.hpp

@@ -22,105 +22,6 @@
 #include <optional>
 
 namespace Acts {
-/// @todo:
-/// 1) Implement the simple Line and Circle fit based on Taubin Circle fit
-/// 2) Implement the simple Line and Parabola fit (from HPS reconstruction by
-/// Robert Johnson)
-
-/// Estimate the track parameters on the xy plane from at least three space
-/// points. It assumes the trajectory projection on the xy plane is a circle,
-/// i.e. the magnetic field is along global z-axis.
-///
-/// The method is based on V. Karimaki NIM A305 (1991) 187-191:
-/// https://doi.org/10.1016/0168-9002(91)90533-V
-/// - no weights are used in Karimaki's fit; d0 is the distance of the point of
-/// closest approach to the origin, 1/R is the curvature, phi is the angle of
-/// the direction propagation (counter clockwise as positive) at the point of
-/// cloest approach.
-///
-/// @tparam spacepoint_iterator_t The type of space point iterator
-///
-/// @param spBegin is the begin iterator for the space points
-/// @param spEnd is the end iterator for the space points
-/// @param logger A logger instance
-///
-/// @return optional bound track parameters with the estimated d0, phi and 1/R
-/// stored with the indices, eBoundLoc0, eBoundPhi and eBoundQOverP,
-/// respectively. The bound parameters with other indices are set to zero.
-template <typename spacepoint_iterator_t>
-std::optional<BoundVector> estimateTrackParamsFromSeed(
-    spacepoint_iterator_t spBegin, spacepoint_iterator_t spEnd,
-    const Logger& logger = getDummyLogger()) {
-  // Check the number of provided space points
-  std::size_t numSP = std::distance(spBegin, spEnd);
-  if (numSP < 3) {
-    ACTS_ERROR("At least three space points are required.");
-    return std::nullopt;
-  }
-
-  ActsScalar x2m = 0., xm = 0.;
-  ActsScalar xym = 0.;
-  ActsScalar y2m = 0., ym = 0.;
-  ActsScalar r2m = 0., r4m = 0.;
-  ActsScalar xr2m = 0., yr2m = 0.;
-
-  for (spacepoint_iterator_t it = spBegin; it != spEnd; it++) {
-    if (*it == nullptr) {
-      ACTS_ERROR("Empty space point found. This should not happen.");
-      return std::nullopt;
-    }
-
-    const auto& sp = *it;
-
-    ActsScalar x = sp->x();
-    ActsScalar y = sp->y();
-    ActsScalar r2 = x * x + y * y;
-    x2m += x * x;
-    xm += x;
-    xym += x * y;
-    y2m += y * y;
-    ym += y;
-    r2m += r2;
-    r4m += r2 * r2;
-    xr2m += x * r2;
-    yr2m += y * r2;
-    numSP++;
-  }
-  x2m = x2m / numSP;
-  xm = xm / numSP;
-  xym = xym / numSP;
-  y2m = y2m / numSP;
-  ym = ym / numSP;
-  r2m = r2m / numSP;
-  r4m = r4m / numSP;
-  xr2m = xr2m / numSP;
-  yr2m = yr2m / numSP;
-
-  ActsScalar Cxx = x2m - xm * xm;
-  ActsScalar Cxy = xym - xm * ym;
-  ActsScalar Cyy = y2m - ym * ym;
-  ActsScalar Cxr2 = xr2m - xm * r2m;
-  ActsScalar Cyr2 = yr2m - ym * r2m;
-  ActsScalar Cr2r2 = r4m - r2m * r2m;
-
-  ActsScalar q1 = Cr2r2 * Cxy - Cxr2 * Cyr2;
-  ActsScalar q2 = Cr2r2 * (Cxx - Cyy) - Cxr2 * Cxr2 + Cyr2 * Cyr2;
-
-  ActsScalar phi = 0.5 * std::atan(2 * q1 / q2);
-  ActsScalar k = (std::sin(phi) * Cxr2 - std::cos(phi) * Cyr2) * (1. / Cr2r2);
-  ActsScalar delta = -k * r2m + std::sin(phi) * xm - std::cos(phi) * ym;
-
-  ActsScalar rho = (2 * k) / (std::sqrt(1 - 4 * delta * k));
-  ActsScalar d0 = (2 * delta) / (1 + std::sqrt(1 - 4 * delta * k));
-
-  // Initialize the bound parameters vector
-  BoundVector params = BoundVector::Zero();
-  params[eBoundLoc0] = d0;
-  params[eBoundPhi] = phi;
-  params[eBoundQOverP] = rho;
-
-  return params;
-}
 
 /// Estimate the full track parameters from three space points
 ///

Tests/UnitTests/Core/Seeding/EstimateTrackParamsFromSeedTest.cpp

@@ -165,36 +165,13 @@ BOOST_AUTO_TEST_CASE(trackparameters_estimation_test) {
           BOOST_TEST_INFO(
               "The truth track parameters at the bottom space point: \n"
               << expParams.transpose());
-          // The curvature of track projection on the transverse plane in unit
-          // of 1/mm
-          double rho = expParams[eBoundQOverP] * 0.3 * 2. / UnitConstants::m;
 
           // The space point pointers
           std::array<const SpacePoint*, 3> spacePointPtrs{};
           std::transform(spacePoints.begin(), std::next(spacePoints.begin(), 3),
                          spacePointPtrs.begin(),
                          [](const auto& sp) { return &sp.second; });
 
-          // Test the partial track parameters estimator
-          auto partialParamsOpt = estimateTrackParamsFromSeed(
-              spacePointPtrs.begin(), spacePointPtrs.end(), *logger);
-          BOOST_REQUIRE(partialParamsOpt.has_value());
-          const auto& estPartialParams = partialParamsOpt.value();
-          BOOST_TEST_INFO(
-              "The estimated track parameters at the transverse plane: \n"
-              << estPartialParams.transpose());
-
-          // The particle starting position is (0, 0, 0). Hence, d0 is zero; the
-          // phi at the point of cloest approach is exactly the phi of the truth
-          // particle
-          CHECK_CLOSE_ABS(estPartialParams[eBoundLoc0], 0., 1e-5);
-          CHECK_CLOSE_ABS(estPartialParams[eBoundPhi], phi, 1e-5);
-          CHECK_CLOSE_ABS(estPartialParams[eBoundQOverP], rho, 1e-4);
-          // The loc1, theta and time are set to zero in the estimator
-          CHECK_CLOSE_ABS(estPartialParams[eBoundLoc1], 0., 1e-10);
-          CHECK_CLOSE_ABS(estPartialParams[eBoundTheta], 0., 1e-10);
-          CHECK_CLOSE_ABS(estPartialParams[eBoundTime], 0., 1e-10);
-
           // Test the full track parameters estimator
           auto fullParamsOpt = estimateTrackParamsFromSeed(
               geoCtx, spacePointPtrs.begin(), spacePointPtrs.end(),