CalculateCoverageDGS.cpp

// Mantid Repository : https://github.com/mantidproject/mantid
//
// Copyright © 2018 ISIS Rutherford Appleton Laboratory UKRI,
//   NScD Oak Ridge National Laboratory, European Spallation Source,
//   Institut Laue - Langevin & CSNS, Institute of High Energy Physics, CAS
// SPDX - License - Identifier: GPL - 3.0 +
#include "MantidMDAlgorithms/CalculateCoverageDGS.h"
#include "MantidAPI/InstrumentValidator.h"
#include "MantidAPI/Run.h"
#include "MantidAPI/Sample.h"
#include "MantidDataObjects/MDHistoWorkspace.h"
#include "MantidGeometry/Crystal/OrientedLattice.h"
#include "MantidGeometry/Instrument.h"
#include "MantidGeometry/Instrument/DetectorInfo.h"
#include "MantidGeometry/Instrument/Goniometer.h"
#include "MantidGeometry/MDGeometry/MDHistoDimension.h"
#include "MantidKernel/ArrayLengthValidator.h"
#include "MantidKernel/ArrayProperty.h"
#include "MantidKernel/BoundedValidator.h"
#include "MantidKernel/ConfigService.h"
#include "MantidKernel/ListValidator.h"
#include "MantidKernel/Strings.h"
#include "MantidKernel/VectorHelper.h"

#include <boost/lexical_cast.hpp>

namespace Mantid::MDAlgorithms {
using namespace Mantid::Kernel;
using Mantid::API::WorkspaceProperty;
using namespace Mantid::API;
using namespace Mantid::DataObjects;
using namespace Mantid::Geometry;

namespace {
// function to compare two intersections (h,k,l,Momentum) by scattered momentum
bool compareMomentum(const Mantid::Kernel::VMD &v1, const Mantid::Kernel::VMD &v2) { return (v1[3] < v2[3]); }
} // namespace
// Register the algorithm into the AlgorithmFactory
DECLARE_ALGORITHM(CalculateCoverageDGS)

/** Constructor
 */
CalculateCoverageDGS::CalculateCoverageDGS()
    : m_hmin(0.f), m_hmax(0.f), m_kmin(0.f), m_kmax(0.f), m_lmin(0.f), m_lmax(0.f), m_dEmin(0.f), m_dEmax(0.f),
      m_Ei(0.), m_ki(0.), m_kfmin(0.), m_kfmax(0.), m_hIntegrated(false), m_kIntegrated(false), m_lIntegrated(false),
      m_dEIntegrated(false), m_hX(), m_kX(), m_lX(), m_eX(), m_hIdx(-1), m_kIdx(-1), m_lIdx(-1), m_eIdx(-1),
      m_rubw(3, 3), m_normWS() {}

/// Algorithms name for identification. @see Algorithm::name
const std::string CalculateCoverageDGS::name() const { return "CalculateCoverageDGS"; }

/// Algorithm's version for identification. @see Algorithm::version
int CalculateCoverageDGS::version() const { return 1; }

/// Algorithm's category for identification. @see Algorithm::category
const std::string CalculateCoverageDGS::category() const { return "Inelastic\\Planning;MDAlgorithms\\Planning"; }

/// Algorithm's summary for use in the GUI and help. @see Algorithm::summary
const std::string CalculateCoverageDGS::summary() const {
  return "Calculate the reciprocal space coverage for direct geometry "
         "spectrometers";
}

/**
 *Stores the X values from each H,K,L dimension as member variables
 */
void CalculateCoverageDGS::cacheDimensionXValues() {
  const double energyToK = 8.0 * M_PI * M_PI * PhysicalConstants::NeutronMass * PhysicalConstants::meV * 1e-20 /
                           (PhysicalConstants::h * PhysicalConstants::h);

  auto &hDim = *m_normWS->getDimension(m_hIdx);
  m_hX.resize(hDim.getNBins());
  for (size_t i = 0; i < m_hX.size(); ++i) {
    m_hX[i] = hDim.getX(i);
  }
  auto &kDim = *m_normWS->getDimension(m_kIdx);
  m_kX.resize(kDim.getNBins());
  for (size_t i = 0; i < m_kX.size(); ++i) {
    m_kX[i] = kDim.getX(i);
  }
  auto &lDim = *m_normWS->getDimension(m_lIdx);
  m_lX.resize(lDim.getNBins());
  for (size_t i = 0; i < m_lX.size(); ++i) {
    m_lX[i] = lDim.getX(i);
  }
  // NOTE: store k final instead
  auto &eDim = *m_normWS->getDimension(m_eIdx);
  m_eX.resize(eDim.getNBins());
  for (size_t i = 0; i < m_eX.size(); ++i) {
    m_eX[i] = std::sqrt(energyToK * (m_Ei - eDim.getX(i)));
  }
}

/** Initialize the algorithm's properties.
 */
void CalculateCoverageDGS::init() {
  declareProperty(std::make_unique<WorkspaceProperty<>>("InputWorkspace", "", Mantid::Kernel::Direction::Input,
                                                        std::make_shared<InstrumentValidator>()),
                  "An input workspace.");

  // clang-format off
  auto mustBe3D = std::make_shared<ArrayLengthValidator<double> >(3);
  // clang-format on
  auto mustBePositive = std::make_shared<BoundedValidator<double>>();
  mustBePositive->setLower(0.0);

  std::vector<double> Q1(3, 0.), Q2(3, 0), Q3(3, 0);
  Q1[0] = 1.;
  Q2[1] = 1.;
  Q3[2] = 1.;
  declareProperty(std::make_unique<ArrayProperty<double>>("Q1Basis", std::move(Q1), mustBe3D->clone()),
                  "Q1 projection direction in the x,y,z format. Q1, Q2, Q3 "
                  "must not be coplanar");
  declareProperty(std::make_unique<ArrayProperty<double>>("Q2Basis", std::move(Q2), mustBe3D->clone()),
                  "Q2 projection direction in the x,y,z format. Q1, Q2, Q3 "
                  "must not be coplanar");
  declareProperty(std::make_unique<ArrayProperty<double>>("Q3Basis", std::move(Q3), std::move(mustBe3D)),
                  "Q3 projection direction in the x,y,z format. Q1, Q2, Q3 "
                  "must not be coplanar");
  declareProperty(std::make_unique<PropertyWithValue<double>>("IncidentEnergy", EMPTY_DBL(), std::move(mustBePositive),
                                                              Mantid::Kernel::Direction::Input),
                  "Incident energy. If set, will override Ei in the input workspace");

  std::vector<std::string> options{"Q1", "Q2", "Q3", "DeltaE"};

  for (int i = 1; i <= 4; i++) {
    std::string dim("Dimension");
    dim += boost::lexical_cast<std::string>(i);
    declareProperty(dim, options[i - 1], std::make_shared<StringListValidator>(options),
                    "Dimension to bin or integrate");
    declareProperty(dim + "Min", EMPTY_DBL(), dim + " minimum value. If empty will take minimum possible value.");
    declareProperty(dim + "Max", EMPTY_DBL(), dim + " maximum value. If empty will take maximum possible value.");
    declareProperty(dim + "Step", EMPTY_DBL(),
                    dim + " step size. If empty the dimension will be "
                          "integrated between minimum and maximum values");
  }
  declareProperty(
      std::make_unique<WorkspaceProperty<Workspace>>("OutputWorkspace", "", Mantid::Kernel::Direction::Output),
      "A name for the output data MDHistoWorkspace.");
}

/** Execute the algorithm.
 */
void CalculateCoverageDGS::exec() {
  const double energyToK = 8.0 * M_PI * M_PI * PhysicalConstants::NeutronMass * PhysicalConstants::meV * 1e-20 /
                           (PhysicalConstants::h * PhysicalConstants::h);
  // get the limits
  Mantid::API::MatrixWorkspace_const_sptr inputWS = getProperty("InputWorkspace");
  convention = Kernel::ConfigService::Instance().getString("Q.convention");
  // cache two theta and phi
  const auto &detectorInfo = inputWS->detectorInfo();
  std::vector<double> tt, phi;
  for (size_t i = 0; i < detectorInfo.size(); ++i) {
    if (!detectorInfo.isMasked(i) && !detectorInfo.isMonitor(i)) {
      const auto &detector = detectorInfo.detector(i);
      tt.emplace_back(detector.getTwoTheta(V3D(0, 0, 0), V3D(0, 0, 1)));
      phi.emplace_back(detector.getPhi());
    }
  }

  double ttmax = *(std::max_element(tt.begin(), tt.end()));
  m_Ei = getProperty("IncidentEnergy");
  if (m_Ei == EMPTY_DBL()) {
    if (inputWS->run().hasProperty("Ei")) {
      Kernel::Property *eiprop = inputWS->run().getProperty("Ei");
      m_Ei = boost::lexical_cast<double>(eiprop->value());
      if (m_Ei <= 0) {
        throw std::invalid_argument("Ei stored in the workspace is not positive");
      }
    } else {
      throw std::invalid_argument("Could not find Ei in the workspace. Please enter a positive value");
    }
  }

  // Check if there is duplicate elements in dimension selection, and calculate
  // the affine matrix
  Kernel::Matrix<coord_t> affineMat(4, 4);
  double q1min(0.), q1max(0.), q2min(0.), q2max(0.), q3min(0.), q3max(0.);
  double q1step(0.), q2step(0.), q3step(0.), dEstep(0.);
  size_t q1NumBins = 1, q2NumBins = 1, q3NumBins = 1, dENumBins = 1;
  for (int i = 1; i <= 4; i++) {
    std::string dim("Dimension");
    dim += boost::lexical_cast<std::string>(i);
    std::string dimensioni = getProperty(dim);
    if (dimensioni == "Q1") {
      affineMat[i - 1][0] = 1.;
      q1min = getProperty(dim + "Min");
      q1max = getProperty(dim + "Max");
      q1step = getProperty(dim + "Step");
      m_hIdx = i - 1;
    }
    if (dimensioni == "Q2") {
      affineMat[i - 1][1] = 1.;
      q2min = getProperty(dim + "Min");
      q2max = getProperty(dim + "Max");
      q2step = getProperty(dim + "Step");
      m_kIdx = i - 1;
    }
    if (dimensioni == "Q3") {
      affineMat[i - 1][2] = 1.;
      q3min = getProperty(dim + "Min");
      q3max = getProperty(dim + "Max");
      q3step = getProperty(dim + "Step");
      m_lIdx = i - 1;
    }
    if (dimensioni == "DeltaE") {
      affineMat[i - 1][3] = 1.;
      m_eIdx = i - 1;
      double dmin = getProperty(dim + "Min");
      if (dmin == EMPTY_DBL()) {
        m_dEmin = -static_cast<coord_t>(m_Ei);
      } else {
        m_dEmin = static_cast<coord_t>(dmin);
      }
      double dmax = getProperty(dim + "Max");
      if (dmax == EMPTY_DBL()) {
        m_dEmax = static_cast<coord_t>(m_Ei);
      } else {
        m_dEmax = static_cast<coord_t>(dmax);
      }
      dEstep = getProperty(dim + "Step");
      if (dEstep == EMPTY_DBL()) {
        dENumBins = 1;
      } else {
        dENumBins = static_cast<size_t>((m_dEmax - m_dEmin) / dEstep);
        if (dEstep * static_cast<double>(dENumBins) + m_dEmin < m_dEmax) {
          dENumBins += 1;
          m_dEmax = static_cast<coord_t>(dEstep * static_cast<double>(dENumBins)) + m_dEmin;
        }
      }
    }
  }

  if (affineMat.determinant() == 0.) {
    g_log.debug() << affineMat;
    throw std::invalid_argument("Please make sure each dimension is selected only once.");
  }

  // Qmax is at  kf=kfmin or kf=kfmax
  m_ki = std::sqrt(energyToK * m_Ei);
  if (m_Ei > m_dEmin) {
    m_kfmin = std::sqrt(energyToK * (m_Ei - m_dEmin));
  } else {
    m_kfmin = 0.;
  }
  if (m_Ei > m_dEmax) {
    m_kfmax = std::sqrt(energyToK * (m_Ei - m_dEmax));
  } else {
    m_kfmax = 0;
  }

  double QmaxTemp = sqrt(m_ki * m_ki + m_kfmin * m_kfmin - 2 * m_ki * m_kfmin * cos(ttmax));
  double Qmax = QmaxTemp;
  QmaxTemp = sqrt(m_ki * m_ki + m_kfmax * m_kfmax - 2 * m_ki * m_kfmax * cos(ttmax));
  if (QmaxTemp > Qmax)
    Qmax = QmaxTemp;

  // get goniometer
  DblMatrix gon = DblMatrix(3, 3, true);
  if (inputWS->run().getGoniometer().isDefined()) {
    gon = inputWS->run().getGoniometerMatrix();
  }

  // get the UB
  DblMatrix UB = DblMatrix(3, 3, true) * (0.5 / M_PI);
  if (inputWS->sample().hasOrientedLattice()) {
    UB = inputWS->sample().getOrientedLattice().getUB();
  }

  // get the W matrix
  DblMatrix W = DblMatrix(3, 3);
  std::vector<double> Q1Basis = getProperty("Q1Basis");
  std::vector<double> Q2Basis = getProperty("Q2Basis");
  std::vector<double> Q3Basis = getProperty("Q3Basis");
  W.setColumn(0, Q1Basis);
  W.setColumn(1, Q2Basis);
  W.setColumn(2, Q3Basis);

  m_rubw = gon * UB * W * (2.0 * M_PI);

  // calculate maximum original limits
  Geometry::OrientedLattice ol;
  ol.setUB(m_rubw);
  m_hmin = static_cast<coord_t>(-Qmax * ol.a());
  m_hmax = static_cast<coord_t>(Qmax * ol.a());
  m_kmin = static_cast<coord_t>(-Qmax * ol.b());
  m_kmax = static_cast<coord_t>(Qmax * ol.b());
  m_lmin = static_cast<coord_t>(-Qmax * ol.c());
  m_lmax = static_cast<coord_t>(Qmax * ol.c());
  m_rubw.Invert();
  // adjust Q steps/dimensions
  if (q1min == EMPTY_DBL()) {
    q1min = m_hmin;
  }
  if (q1max == EMPTY_DBL()) {
    q1max = m_hmax;
  }
  if (q1min >= q1max) {
    throw std::invalid_argument("Q1max has to be greater than Q1min");
  }
  if (q1step == EMPTY_DBL()) {
    q1NumBins = 1;
  } else {
    q1NumBins = static_cast<size_t>((q1max - q1min) / q1step);
    if (q1step * static_cast<double>(q1NumBins) + q1min < q1max) {
      q1NumBins += 1;
      q1max = q1step * static_cast<double>(q1NumBins) + q1min;
    }
  }

  if (q2min == EMPTY_DBL()) {
    q2min = m_kmin;
  }
  if (q2max == EMPTY_DBL()) {
    q2max = m_kmax;
  }
  if (q2min >= q2max) {
    throw std::invalid_argument("Q2max has to be greater than Q2min");
  }
  if (q2step == EMPTY_DBL()) {
    q2NumBins = 1;
  } else {
    q2NumBins = static_cast<size_t>((q2max - q2min) / q2step);
    if (q2step * static_cast<double>(q2NumBins) + q2min < q2max) {
      q2NumBins += 1;
      q2max = q2step * static_cast<double>(q2NumBins) + q2min;
    }
  }

  if (q3min == EMPTY_DBL()) {
    q3min = m_lmin;
  }
  if (q3max == EMPTY_DBL()) {
    q3max = m_lmax;
  }
  if (q3min >= q3max) {
    throw std::invalid_argument("Q3max has to be greater than Q3min");
  }
  if (q3step == EMPTY_DBL()) {
    q3NumBins = 1;
  } else {
    q3NumBins = static_cast<size_t>((q3max - q3min) / q3step);
    if (q3step * static_cast<double>(q3NumBins) + q3min < q3max) {
      q3NumBins += 1;
      q3max = q3step * static_cast<double>(q3NumBins) + q3min;
    }
  }

  // create the output workspace
  std::vector<Mantid::Geometry::MDHistoDimension_sptr> binDimensions;

  // Define frames
  Mantid::Geometry::GeneralFrame frame1("Q1", "");
  Mantid::Geometry::GeneralFrame frame2("Q2", "");
  Mantid::Geometry::GeneralFrame frame3("Q3", "");
  Mantid::Geometry::GeneralFrame frame4("meV", "");
  auto out1 = std::make_shared<MDHistoDimension>("Q1", "Q1", frame1, static_cast<coord_t>(q1min),
                                                 static_cast<coord_t>(q1max), q1NumBins);
  auto out2 = std::make_shared<MDHistoDimension>("Q2", "Q2", frame2, static_cast<coord_t>(q2min),
                                                 static_cast<coord_t>(q2max), q2NumBins);
  auto out3 = std::make_shared<MDHistoDimension>("Q3", "Q3", frame3, static_cast<coord_t>(q3min),
                                                 static_cast<coord_t>(q3max), q3NumBins);
  auto out4 = std::make_shared<MDHistoDimension>("DeltaE", "DeltaE", frame4, static_cast<coord_t>(m_dEmin),
                                                 static_cast<coord_t>(m_dEmax), dENumBins);

  for (size_t row = 0; row <= 3; row++) {
    if (affineMat[row][0] == 1.) {
      binDimensions.emplace_back(out1);
    }
    if (affineMat[row][1] == 1.) {
      binDimensions.emplace_back(out2);
    }
    if (affineMat[row][2] == 1.) {
      binDimensions.emplace_back(out3);
    }
    if (affineMat[row][3] == 1.) {
      binDimensions.emplace_back(out4);
    }
  }

  m_normWS = std::make_shared<MDHistoWorkspace>(binDimensions);
  m_normWS->setTo(0., 0., 0.);
  setProperty("OutputWorkspace", std::dynamic_pointer_cast<Workspace>(m_normWS));

  cacheDimensionXValues();

  const auto ndets = static_cast<int64_t>(tt.size());

  PARALLEL_FOR_IF(Kernel::threadSafe(*inputWS))
  for (int64_t i = 0; i < ndets; i++) {
    PARALLEL_START_INTERRUPT_REGION
    auto intersections = calculateIntersections(tt[i], phi[i]);
    if (intersections.empty())
      continue;
    auto intersectionsBegin = intersections.begin();
    for (auto it = intersectionsBegin + 1; it != intersections.end(); ++it) {
      const auto &curIntSec = *it;
      const auto &prevIntSec = *(it - 1);
      // the full vector isn't used so compute only what is necessary
      double delta = curIntSec[3] - prevIntSec[3];
      if (delta < 1e-10)
        continue; // Assume zero contribution if difference is small
      // Average between two intersections for final position
      std::vector<coord_t> pos(4);
      std::transform(curIntSec.getBareArray(), curIntSec.getBareArray() + 4, prevIntSec.getBareArray(), pos.begin(),
                     [](const double lhs, const double rhs) { return static_cast<coord_t>(0.5 * (lhs + rhs)); });
      // transform kf to energy transfer
      pos[3] = static_cast<coord_t>(m_Ei - pos[3] * pos[3] / energyToK);

      std::vector<coord_t> posNew = affineMat * pos;
      size_t linIndex = m_normWS->getLinearIndexAtCoord(posNew.data());
      if (linIndex == size_t(-1))
        continue;
      PARALLEL_CRITICAL(updateMD) { m_normWS->setSignalAt(linIndex, 1.); }
    }
    PARALLEL_END_INTERRUPT_REGION
  }
  PARALLEL_CHECK_INTERRUPT_REGION
}

/**
 *Calculate the points of intersection for the given detector with cuboid
 * surrounding the
 *detector position in HKL
 *@param theta Polar angle withd detector
 *@param phi Azimuthal angle with detector
 *@return A list of intersections in HKL+kf space
 */
std::vector<Kernel::VMD> CalculateCoverageDGS::calculateIntersections(const double theta, const double phi) {
  V3D qout(sin(theta) * cos(phi), sin(theta) * sin(phi), cos(theta)), qin(0., 0., m_ki);
  qout = m_rubw * qout;
  qin = m_rubw * qin;
  if (convention == "Crystallography") {
    qout *= -1;
    qin *= -1;
  }
  double hStart = qin.X() - qout.X() * m_kfmin, hEnd = qin.X() - qout.X() * m_kfmax;
  double kStart = qin.Y() - qout.Y() * m_kfmin, kEnd = qin.Y() - qout.Y() * m_kfmax;
  double lStart = qin.Z() - qout.Z() * m_kfmin, lEnd = qin.Z() - qout.Z() * m_kfmax;
  double eps = 1e-10;
  auto hNBins = m_hX.size();
  auto kNBins = m_kX.size();
  auto lNBins = m_lX.size();
  auto eNBins = m_eX.size();
  std::vector<Kernel::VMD> intersections;
  intersections.reserve(hNBins + kNBins + lNBins + eNBins + 8); // 8 is 3*(min,max for each Q component)+kfmin+kfmax

  // calculate intersections with planes perpendicular to h
  if (fabs(hStart - hEnd) > eps) {
    double fmom = (m_kfmax - m_kfmin) / (hEnd - hStart);
    double fk = (kEnd - kStart) / (hEnd - hStart);
    double fl = (lEnd - lStart) / (hEnd - hStart);
    if (!m_hIntegrated) {
      for (size_t i = 0; i < hNBins; i++) {
        double hi = m_hX[i];
        if ((hi >= m_hmin) && (hi <= m_hmax) && ((hStart - hi) * (hEnd - hi) < 0)) {
          // if hi is between hStart and hEnd, then ki and li will be between
          // kStart, kEnd and lStart, lEnd and momi will be between m_kfmin and
          // m_kfmax
          double ki = fk * (hi - hStart) + kStart;
          double li = fl * (hi - hStart) + lStart;
          if ((ki >= m_kmin) && (ki <= m_kmax) && (li >= m_lmin) && (li <= m_lmax)) {
            double momi = fmom * (hi - hStart) + m_kfmin;
            intersections.emplace_back(hi, ki, li, momi);
          }
        }
      }
    }
    double momhMin = fmom * (m_hmin - hStart) + m_kfmin;
    if ((momhMin - m_kfmin) * (momhMin - m_kfmax) < 0) // m_kfmin>m_kfmax
    {
      // khmin and lhmin
      double khmin = fk * (m_hmin - hStart) + kStart;
      double lhmin = fl * (m_hmin - hStart) + lStart;
      if ((khmin >= m_kmin) && (khmin <= m_kmax) && (lhmin >= m_lmin) && (lhmin <= m_lmax)) {
        intersections.emplace_back(m_hmin, khmin, lhmin, momhMin);
      }
    }
    double momhMax = fmom * (m_hmax - hStart) + m_kfmin;
    if ((momhMax - m_kfmin) * (momhMax - m_kfmax) <= 0) {
      // khmax and lhmax
      double khmax = fk * (m_hmax - hStart) + kStart;
      double lhmax = fl * (m_hmax - hStart) + lStart;
      if ((khmax >= m_kmin) && (khmax <= m_kmax) && (lhmax >= m_lmin) && (lhmax <= m_lmax)) {
        intersections.emplace_back(m_hmax, khmax, lhmax, momhMax);
      }
    }
  }

  // calculate intersections with planes perpendicular to k
  if (fabs(kStart - kEnd) > eps) {
    double fmom = (m_kfmax - m_kfmin) / (kEnd - kStart);
    double fh = (hEnd - hStart) / (kEnd - kStart);
    double fl = (lEnd - lStart) / (kEnd - kStart);
    if (!m_kIntegrated) {
      for (size_t i = 0; i < kNBins; i++) {
        double ki = m_kX[i];
        if ((ki >= m_kmin) && (ki <= m_kmax) && ((kStart - ki) * (kEnd - ki) < 0)) {
          // if ki is between kStart and kEnd, then hi and li will be between
          // hStart, hEnd and lStart, lEnd and momi will be between m_kfmin and
          // m_kfmax
          double hi = fh * (ki - kStart) + hStart;
          double li = fl * (ki - kStart) + lStart;
          if ((hi >= m_hmin) && (hi <= m_hmax) && (li >= m_lmin) && (li <= m_lmax)) {
            double momi = fmom * (ki - kStart) + m_kfmin;
            intersections.emplace_back(hi, ki, li, momi);
          }
        }
      }
    }
    double momkMin = fmom * (m_kmin - kStart) + m_kfmin;
    if ((momkMin - m_kfmin) * (momkMin - m_kfmax) < 0) {
      // hkmin and lkmin
      double hkmin = fh * (m_kmin - kStart) + hStart;
      double lkmin = fl * (m_kmin - kStart) + lStart;
      if ((hkmin >= m_hmin) && (hkmin <= m_hmax) && (lkmin >= m_lmin) && (lkmin <= m_lmax)) {
        intersections.emplace_back(hkmin, m_kmin, lkmin, momkMin);
      }
    }
    double momkMax = fmom * (m_kmax - kStart) + m_kfmin;
    if ((momkMax - m_kfmin) * (momkMax - m_kfmax) <= 0) {
      // hkmax and lkmax
      double hkmax = fh * (m_kmax - kStart) + hStart;
      double lkmax = fl * (m_kmax - kStart) + lStart;
      if ((hkmax >= m_hmin) && (hkmax <= m_hmax) && (lkmax >= m_lmin) && (lkmax <= m_lmax)) {
        intersections.emplace_back(hkmax, m_kmax, lkmax, momkMax);
      }
    }
  }

  // calculate intersections with planes perpendicular to l
  if (fabs(lStart - lEnd) > eps) {
    double fmom = (m_kfmax - m_kfmin) / (lEnd - lStart);
    double fh = (hEnd - hStart) / (lEnd - lStart);
    double fk = (kEnd - kStart) / (lEnd - lStart);
    if (!m_lIntegrated) {
      for (size_t i = 0; i < lNBins; i++) {
        double li = m_lX[i];
        if ((li >= m_lmin) && (li <= m_lmax) && ((lStart - li) * (lEnd - li) < 0)) {
          double hi = fh * (li - lStart) + hStart;
          double ki = fk * (li - lStart) + kStart;
          if ((hi >= m_hmin) && (hi <= m_hmax) && (ki >= m_kmin) && (ki <= m_kmax)) {
            double momi = fmom * (li - lStart) + m_kfmin;
            intersections.emplace_back(hi, ki, li, momi);
          }
        }
      }
    }
    double momlMin = fmom * (m_lmin - lStart) + m_kfmin;
    if ((momlMin - m_kfmin) * (momlMin - m_kfmax) <= 0) {
      // hlmin and klmin
      double hlmin = fh * (m_lmin - lStart) + hStart;
      double klmin = fk * (m_lmin - lStart) + kStart;
      if ((hlmin >= m_hmin) && (hlmin <= m_hmax) && (klmin >= m_kmin) && (klmin <= m_kmax)) {
        intersections.emplace_back(hlmin, klmin, m_lmin, momlMin);
      }
    }
    double momlMax = fmom * (m_lmax - lStart) + m_kfmin;
    if ((momlMax - m_kfmin) * (momlMax - m_kfmax) < 0) {
      // hlmax and klmax
      double hlmax = fh * (m_lmax - lStart) + hStart;
      double klmax = fk * (m_lmax - lStart) + kStart;
      if ((hlmax >= m_hmin) && (hlmax <= m_hmax) && (klmax >= m_kmin) && (klmax <= m_kmax)) {
        intersections.emplace_back(hlmax, klmax, m_lmax, momlMax);
      }
    }
  }

  // intersections with dE
  if (!m_dEIntegrated) {
    for (size_t i = 0; i < eNBins; i++) {
      double kfi = m_eX[i];
      if ((kfi - m_kfmin) * (kfi - m_kfmax) <= 0) {
        double h = qin.X() - qout.X() * kfi;
        double k = qin.Y() - qout.Y() * kfi;
        double l = qin.Z() - qout.Z() * kfi;
        if ((h >= m_hmin) && (h <= m_hmax) && (k >= m_kmin) && (k <= m_kmax) && (l >= m_lmin) && (l <= m_lmax)) {
          intersections.emplace_back(h, k, l, kfi);
        }
      }
    }
  }

  // endpoints
  if ((hStart >= m_hmin) && (hStart <= m_hmax) && (kStart >= m_kmin) && (kStart <= m_kmax) && (lStart >= m_lmin) &&
      (lStart <= m_lmax)) {
    intersections.emplace_back(hStart, kStart, lStart, m_kfmin);
  }
  if ((hEnd >= m_hmin) && (hEnd <= m_hmax) && (kEnd >= m_kmin) && (kEnd <= m_kmax) && (lEnd >= m_lmin) &&
      (lEnd <= m_lmax)) {
    intersections.emplace_back(hEnd, kEnd, lEnd, m_kfmax);
  }

  // sort intersections by final momentum
  using IterType = std::vector<Mantid::Kernel::VMD>::iterator;
  std::stable_sort<IterType, bool (*)(const Mantid::Kernel::VMD &, const Mantid::Kernel::VMD &)>(
      intersections.begin(), intersections.end(), compareMomentum);

  return intersections;
}

} // namespace Mantid::MDAlgorithms