SofQWNormalisedPolygon.cpp

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// 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 "MantidAlgorithms/SofQWNormalisedPolygon.h"
#include "MantidAPI/AnalysisDataService.h"
#include "MantidAPI/FrameworkManager.h"
#include "MantidAPI/SpectrumDetectorMapping.h"
#include "MantidAPI/SpectrumInfo.h"
#include "MantidAPI/WorkspaceFactory.h"
#include "MantidAPI/WorkspaceNearestNeighbourInfo.h"
#include "MantidAlgorithms/SofQW.h"
#include "MantidDataObjects/FractionalRebinning.h"
#include "MantidDataObjects/TableWorkspace.h"
#include "MantidGeometry/Crystal/AngleUnits.h"
#include "MantidGeometry/Instrument.h"
#include "MantidGeometry/Instrument/DetectorGroup.h"
#include "MantidGeometry/Instrument/DetectorInfo.h"
#include "MantidGeometry/Instrument/ReferenceFrame.h"
#include "MantidGeometry/Objects/BoundingBox.h"
#include "MantidGeometry/Objects/CSGObject.h"
#include "MantidGeometry/Objects/IObject.h"
#include "MantidIndexing/IndexInfo.h"
#include "MantidKernel/PhysicalConstants.h"
#include "MantidTypes/SpectrumDefinition.h"
 
#include <boost/math/special_functions/pow.hpp>
 
using boost::math::pow;
using Mantid::Geometry::rad2deg;
 
namespace {
double twoThetaFromLocalPoint(const Mantid::Geometry::DetectorInfo &detInfo, const size_t detInfoIndex,
                              const Mantid::Kernel::V3D &samplePos, const Mantid::Kernel::V3D &beamDir,
                              Mantid::Kernel::V3D point) {
  const auto rotation = detInfo.rotation(detInfoIndex);
  const auto position = detInfo.position(detInfoIndex);
  rotation.rotate(point);
  point += position;
  point -= samplePos;
  const auto twoTheta = point.angle(beamDir);
  return twoTheta;
}
 
std::pair<double, double> cuboidTwoThetaRange(const Mantid::Geometry::DetectorInfo &detInfo, const size_t detInfoIndex,
                                              const Mantid::Kernel::V3D &samplePos, const Mantid::Kernel::V3D &beamDir,
                                              const Mantid::Geometry::detail::ShapeInfo::CuboidGeometry &geometry) {
  const auto back = geometry.leftBackBottom - geometry.leftFrontBottom;
  const auto up = geometry.leftFrontTop - geometry.leftFrontBottom;
  const auto right = geometry.rightFrontBottom - geometry.leftFrontBottom;
  const std::array<Mantid::Kernel::V3D, 8> capRing{{geometry.leftFrontBottom, geometry.leftFrontBottom + back * 0.5,
                                                    geometry.leftBackBottom, geometry.leftBackBottom + up * 0.5,
                                                    geometry.leftBackBottom + up, geometry.leftFrontTop + back * 0.5,
                                                    geometry.leftFrontTop, geometry.leftFrontBottom + up * 0.5}};
  double minTwoTheta{std::numeric_limits<double>::max()};
  double maxTwoTheta{std::numeric_limits<double>::lowest()};
  for (int width = 0; width < 2; ++width) {
    const auto offset = right * static_cast<double>(width);
    for (const auto &pointInRing : capRing) {
      auto point = pointInRing;
      if (width != 0) {
        point += offset;
      }
      const auto current = twoThetaFromLocalPoint(detInfo, detInfoIndex, samplePos, beamDir, point);
      minTwoTheta = std::min(minTwoTheta, current);
      maxTwoTheta = std::max(maxTwoTheta, current);
    }
  }
  const auto beltOffset = right * 0.5;
  for (size_t beltIndex = 0; beltIndex < capRing.size(); beltIndex += 2) {
    const auto point = capRing[beltIndex] + beltOffset;
    const auto current = twoThetaFromLocalPoint(detInfo, detInfoIndex, samplePos, beamDir, point);
    minTwoTheta = std::min(minTwoTheta, current);
    maxTwoTheta = std::max(maxTwoTheta, current);
  }
  return std::make_pair(minTwoTheta, maxTwoTheta);
}
 
std::pair<double, double> cylinderTwoThetaRange(const Mantid::Geometry::DetectorInfo &detInfo,
                                                const size_t detInfoIndex, const Mantid::Kernel::V3D &samplePos,
                                                const Mantid::Kernel::V3D &beamDir,
                                                const Mantid::Geometry::detail::ShapeInfo::CylinderGeometry &geometry) {
  Mantid::Kernel::V3D basis1{1., 0., 0.};
  if (geometry.axis.X() != 0. && geometry.axis.Z() != 0) {
    const auto inverseXZSumSq = 1. / (pow<2>(geometry.axis.X()) + pow<2>(geometry.axis.Z()));
    basis1.setX(std::sqrt(1. - pow<2>(geometry.axis.X()) * inverseXZSumSq));
    basis1.setY(geometry.axis.X() * std::sqrt(inverseXZSumSq));
  }
  const Mantid::Kernel::V3D basis2 = geometry.axis.cross_prod(basis1);
  const std::array<double, 8> angles{
      {0., 0.25 * M_PI, 0.5 * M_PI, 0.75 * M_PI, M_PI, 1.25 * M_PI, 1.5 * M_PI, 1.75 * M_PI}};
  double minTwoTheta{std::numeric_limits<double>::max()};
  double maxTwoTheta{std::numeric_limits<double>::lowest()};
  for (const double &angle : angles) {
    const auto basePoint =
        geometry.centreOfBottomBase + (basis1 * std::cos(angle) + basis2 * std::sin(angle)) * geometry.radius;
    for (int i = 0; i < 3; ++i) {
      const auto point = basePoint + geometry.axis * (0.5 * geometry.height * static_cast<double>(i));
      const auto current = twoThetaFromLocalPoint(detInfo, detInfoIndex, samplePos, beamDir, point);
      minTwoTheta = std::min(minTwoTheta, current);
      maxTwoTheta = std::max(maxTwoTheta, current);
    }
  }
  return std::make_pair(minTwoTheta, maxTwoTheta);
}
 
double twoThetaFromBoundingBox(const Mantid::Geometry::DetectorInfo &detInfo, const size_t detInfoIndex,
                               const Mantid::Kernel::V3D &samplePos, const Mantid::Kernel::V3D &beamDir,
                               const Mantid::Kernel::V3D &sideDir) {
  const auto shape = detInfo.detector(detInfoIndex).shape();
  const Mantid::Geometry::BoundingBox bbox = shape->getBoundingBox();
  const auto maxPoint = bbox.maxPoint();
  auto side = maxPoint * sideDir;
  return twoThetaFromLocalPoint(detInfo, detInfoIndex, samplePos, beamDir, side);
}
 
std::pair<double, double> generalTwoThetaRange(const Mantid::Geometry::DetectorInfo &detInfo, const size_t detInfoIndex,
                                               const Mantid::Kernel::V3D &samplePos,
                                               const Mantid::Kernel::V3D &beamDir) {
  double minTwoTheta{std::numeric_limits<double>::max()};
  double maxTwoTheta{std::numeric_limits<double>::lowest()};
  const std::array<Mantid::Kernel::V3D, 6> dirs{
      {Mantid::Kernel::V3D{1., 0., 0.}, {0., 1., 0.}, {0., 0., 1.}, {-1., 0., 0.}, {0., -1., 0.}, {0., 0., -1.}}};
  for (const auto &dir : dirs) {
    const auto current = twoThetaFromBoundingBox(detInfo, detInfoIndex, samplePos, beamDir, dir);
    minTwoTheta = std::min(minTwoTheta, current);
    maxTwoTheta = std::max(maxTwoTheta, current);
  }
  return std::make_pair(minTwoTheta, maxTwoTheta);
}
 
std::pair<double, double> minMaxTwoTheta(const Mantid::Geometry::DetectorInfo &detInfo, const size_t detInfoIndex,
                                         const Mantid::Kernel::V3D &samplePos, const Mantid::Kernel::V3D &beamDir) {
  const auto shape = detInfo.detector(detInfoIndex).shape();
  const Mantid::Geometry::CSGObject *csgShape;
  switch (shape->shape()) {
  case Mantid::Geometry::detail::ShapeInfo::GeometryShape::CYLINDER:
    csgShape = dynamic_cast<const Mantid::Geometry::CSGObject *>(shape.get());
    assert(csgShape);
    return cylinderTwoThetaRange(detInfo, detInfoIndex, samplePos, beamDir, csgShape->shapeInfo().cylinderGeometry());
  case Mantid::Geometry::detail::ShapeInfo::GeometryShape::CUBOID:
    csgShape = dynamic_cast<const Mantid::Geometry::CSGObject *>(shape.get());
    assert(csgShape);
    return cuboidTwoThetaRange(detInfo, detInfoIndex, samplePos, beamDir, csgShape->shapeInfo().cuboidGeometry());
  default:
    return generalTwoThetaRange(detInfo, detInfoIndex, samplePos, beamDir);
  }
}
 
std::pair<double, double> twoThetasFromTable(const Mantid::detid_t detID, const std::vector<int> &detectorIDs,
                                             const std::vector<double> &lowers, const std::vector<double> &uppers) {
  const auto range = std::equal_range(detectorIDs.cbegin(), detectorIDs.cend(), static_cast<int>(detID));
  if (std::distance(range.first, range.second) > 1) {
    throw std::invalid_argument("Duplicate detector IDs in 'DetectorTwoThetaRanges'.");
  }
  if (range.first == detectorIDs.cend()) {
    throw std::invalid_argument("No min/max 2thetas found for detector ID " + std::to_string(detID));
  }
  const auto index = std::distance(detectorIDs.cbegin(), range.first);
  const auto minmax = std::make_pair(lowers[index], uppers[index]);
  if (minmax.first <= 0) {
    throw std::invalid_argument("Non-positive min 2theta for detector ID " + std::to_string(detID));
  }
  if (minmax.first > M_PI) {
    throw std::invalid_argument("Min 2theta greater than pi for detector ID " + std::to_string(detID));
  }
  if (minmax.second > M_PI) {
    throw std::invalid_argument("Max 2theta greater than pi for detector ID" + std::to_string(detID));
  }
  if (minmax.first >= minmax.second) {
    throw std::invalid_argument("Min 2theta larger than max for detector ID " + std::to_string(detID));
  }
  return minmax;
}
} // namespace
 
namespace Mantid::Algorithms {
// Setup typedef for later use
using SpectraDistanceMap = std::map<specnum_t, Mantid::Kernel::V3D>;
using DetConstPtr = Geometry::IDetector_const_sptr;
 
// Register the algorithm into the AlgorithmFactory
DECLARE_ALGORITHM(SofQWNormalisedPolygon)
 
using namespace Mantid::Kernel;
using namespace Mantid::Geometry;
using namespace Mantid::API;
using namespace Mantid::DataObjects;
 
const std::string SofQWNormalisedPolygon::name() const { return "SofQWNormalisedPolygon"; }
 
int SofQWNormalisedPolygon::version() const { return 1; }
 
const std::string SofQWNormalisedPolygon::category() const { return "Inelastic\\SofQW"; }
 
void SofQWNormalisedPolygon::init() { SofQW::createCommonInputProperties(*this); }
 
std::map<std::string, std::string> SofQWNormalisedPolygon::validateInputs() {
  std::map<std::string, std::string> result;
  API::MatrixWorkspace_const_sptr inputWS = getProperty("InputWorkspace");
  if (!inputWS) {
    result["InputWorkspace"] = "InputWorkspace is of Incorrect type. Please "
                               "provide a MatrixWorkspace as the "
                               "InputWorkspace";
  }
  TableWorkspace_sptr tableWS = getProperty("DetectorTwoThetaRanges");
  if (tableWS) {
    // The table should have three columns
    if (tableWS->columnCount() != 3) {
      result["DetectorTwoThetaRanges"] = "DetectorTwoThetaRanges requires 3 columns";
    }
    // The first column should be of type int
    else if (!tableWS->getColumn(0)->isType<int>()) {
      result["DetectorTwoThetaRanges"] = "The first column of DetectorTwoThetaRanges should be of type int";
    }
    // The second column should be of type double
    else if (!tableWS->getColumn(1)->isType<double>()) {
      result["DetectorTwoThetaRanges"] = "The second column of DetectorTwoThetaRanges should be of type "
                                         "double";
    }
    // The third column should be of type double.
    else if (!tableWS->getColumn(2)->isType<double>()) {
      result["DetectorTwoThetaRanges"] = "The third column of DetectorTwoThetaRanges should be of type double";
    }
    // Table and workspace should have the same number of detectors.
    else if (tableWS->rowCount() != inputWS->getNumberHistograms()) {
      result["DetectorTwoThetaRanges"] = "The table and workspace do not have the same number of detectors";
    }
  }
  return result;
}
 
void SofQWNormalisedPolygon::exec() {
  MatrixWorkspace_const_sptr inputWS = getProperty("InputWorkspace");
  // Compute input caches
  m_EmodeProperties.initCachedValues(*inputWS, this);
 
  RebinnedOutput_sptr outputWS = SofQW::setUpOutputWorkspace<RebinnedOutput>(
      *inputWS, getProperty("QAxisBinning"), m_Qout, getProperty("EAxisBinning"), m_EmodeProperties);
  g_log.debug() << "Workspace type: " << outputWS->id() << '\n';
  setProperty("OutputWorkspace", outputWS);
  const size_t nEnergyBins = inputWS->blocksize();
  const size_t nHistos = inputWS->getNumberHistograms();
 
  // Holds the spectrum-detector mapping
  std::vector<SpectrumDefinition> detIDMapping(outputWS->getNumberHistograms());
 
  // Progress reports & cancellation
  const size_t nreports(nHistos * nEnergyBins);
  m_progress = std::make_unique<API::Progress>(this, 0.0, 1.0, nreports);
 
  // Index theta cache
  TableWorkspace_sptr twoThetaTable = getProperty("DetectorTwoThetaRanges");
  if (twoThetaTable) {
    initAngularCachesTable(*inputWS, *twoThetaTable);
  } else {
    std::vector<double> par = inputWS->getInstrument()->getNumberParameter("detector-neighbour-offset");
    if (par.empty()) {
      this->initAngularCachesNonPSD(*inputWS);
    } else {
      g_log.debug() << "Offset: " << par[0] << '\n';
      this->m_detNeighbourOffset = static_cast<int>(par[0]);
      this->initAngularCachesPSD(*inputWS);
    }
  }
  const auto &X = inputWS->x(0);
 
  const auto &inputIndices = inputWS->indexInfo();
  const auto &spectrumInfo = inputWS->spectrumInfo();
 
  PARALLEL_FOR_IF(Kernel::threadSafe(*inputWS, *outputWS))
  for (int64_t i = 0; i < static_cast<int64_t>(nHistos); ++i) {
    PARALLEL_START_INTERRUPT_REGION
 
    if (spectrumInfo.isMasked(i) || spectrumInfo.isMonitor(i)) {
      continue;
    }
    const auto *det = m_EmodeProperties.m_emode == 1 ? nullptr : &spectrumInfo.detector(i);
 
    const double thetaLower = m_twoThetaLowers[i];
    const double thetaUpper = m_twoThetaUppers[i];
 
    const auto specNo = static_cast<specnum_t>(inputIndices.spectrumNumber(i));
    std::stringstream logStream;
    for (size_t j = 0; j < nEnergyBins; ++j) {
      m_progress->report("Computing polygon intersections");
      // For each input polygon test where it intersects with
      // the output grid and assign the appropriate weights of Y/E
      const double dE_j = X[j];
      const double dE_jp1 = X[j + 1];
 
      const double lrQ = m_EmodeProperties.q(dE_jp1, thetaLower, det);
 
      const V2D ll(dE_j, m_EmodeProperties.q(dE_j, thetaLower, det));
      const V2D lr(dE_jp1, lrQ);
      const V2D ur(dE_jp1, m_EmodeProperties.q(dE_jp1, thetaUpper, det));
      const V2D ul(dE_j, m_EmodeProperties.q(dE_j, thetaUpper, det));
      if (g_log.is(Logger::Priority::PRIO_DEBUG)) {
        logStream << "Spectrum=" << specNo << ", lower theta=" << thetaLower * rad2deg
                  << ", upper theta=" << thetaUpper * rad2deg << ". QE polygon: ll=" << ll << ", lr=" << lr
                  << ", ur=" << ur << ", ul=" << ul << "\n";
      }
 
      using FractionalRebinning::rebinToFractionalOutput;
      rebinToFractionalOutput(Quadrilateral(ll, lr, ur, ul), inputWS, i, j, *outputWS, m_Qout);
 
      // Find which q bin this point lies in
      const MantidVec::difference_type qIndex = std::upper_bound(m_Qout.begin(), m_Qout.end(), lrQ) - m_Qout.begin();
      if (qIndex != 0 && qIndex < static_cast<int>(m_Qout.size())) {
        // Add this spectra-detector pair to the mapping
        PARALLEL_CRITICAL(SofQWNormalisedPolygon_spectramap) {
          // Could do a more complete merge of spectrum definitions here, but
          // historically only the ID of the first detector in the spectrum is
          // used, so I am keeping that for now.
          detIDMapping[qIndex - 1].add(spectrumInfo.spectrumDefinition(i)[0].first);
        }
      }
    }
    if (g_log.is(Logger::Priority::PRIO_DEBUG)) {
      g_log.debug(logStream.str());
    }
 
    PARALLEL_END_INTERRUPT_REGION
  }
  PARALLEL_CHECK_INTERRUPT_REGION
 
  FractionalRebinning::finalizeFractionalRebin(*outputWS);
  outputWS->finalize();
  FractionalRebinning::normaliseOutput(outputWS, inputWS, m_progress.get());
 
  // Set the output spectrum-detector mapping
  auto outputIndices = outputWS->indexInfo();
  outputIndices.setSpectrumDefinitions(std::move(detIDMapping));
  outputWS->setIndexInfo(outputIndices);
 
  // Replace any NaNs in outputWorkspace with zeroes
  if (this->getProperty("ReplaceNaNs")) {
    auto replaceNans = this->createChildAlgorithm("ReplaceSpecialValues");
    replaceNans->setChild(true);
    replaceNans->initialize();
    replaceNans->setProperty("InputWorkspace", outputWS);
    replaceNans->setProperty("OutputWorkspace", outputWS);
    replaceNans->setProperty("NaNValue", 0.0);
    replaceNans->setProperty("InfinityValue", 0.0);
    replaceNans->setProperty("BigNumberThreshold", DBL_MAX);
    replaceNans->execute();
  }
}
 
void SofQWNormalisedPolygon::initAngularCachesNonPSD(const MatrixWorkspace &workspace) {
  const size_t nhist = workspace.getNumberHistograms();
  constexpr double skipDetector{-1.};
  m_twoThetaLowers = std::vector<double>(nhist, skipDetector);
  m_twoThetaUppers = std::vector<double>(nhist, skipDetector);
 
  auto inst = workspace.getInstrument();
  const auto referenceFrame = inst->getReferenceFrame();
  const auto beamDir = referenceFrame->vecPointingAlongBeam();
 
  const auto &detectorInfo = workspace.detectorInfo();
  const auto &spectrumInfo = workspace.spectrumInfo();
  const auto samplePos = spectrumInfo.samplePosition();
  for (size_t i = 0; i < nhist; ++i) {
    m_progress->report("Calculating detector angles");
 
    // If no detector found, skip onto the next spectrum
    if (!spectrumInfo.hasDetectors(i) || spectrumInfo.isMonitor(i)) {
      continue;
    }
 
    const auto &det = spectrumInfo.detector(i);
    // Check to see if there is an EFixed, if not skip it
    try {
      m_EmodeProperties.getEFixed(det);
    } catch (std::runtime_error &) {
      continue;
    }
 
    double minTwoTheta{spectrumInfo.twoTheta(i)};
    double maxTwoTheta{minTwoTheta};
    if (spectrumInfo.hasUniqueDetector(i)) {
      const auto detInfoIndex = detectorInfo.indexOf(det.getID());
      std::tie(minTwoTheta, maxTwoTheta) = minMaxTwoTheta(detectorInfo, detInfoIndex, samplePos, beamDir);
    } else {
      const auto &group = dynamic_cast<const DetectorGroup &>(det);
      const auto ids = group.getDetectorIDs();
      for (const auto id : ids) {
        const auto detInfoIndex = detectorInfo.indexOf(id);
        const auto current = minMaxTwoTheta(detectorInfo, detInfoIndex, samplePos, beamDir);
        minTwoTheta = std::min(minTwoTheta, current.first);
        maxTwoTheta = std::max(maxTwoTheta, current.second);
      }
    }
    m_twoThetaLowers[i] = minTwoTheta;
    m_twoThetaUppers[i] = maxTwoTheta;
    if (g_log.is(Logger::Priority::PRIO_DEBUG)) {
      g_log.debug() << "Detector at spectrum = " << workspace.getSpectrum(i).getSpectrumNo()
                    << ", lower 2theta = " << m_twoThetaLowers[i] * rad2deg
                    << ", upper 2theta = " << m_twoThetaUppers[i] * rad2deg << " degrees\n";
    }
  }
}
 
void SofQWNormalisedPolygon::initAngularCachesPSD(const MatrixWorkspace &workspace) {
  const size_t nHistos = workspace.getNumberHistograms();
 
  bool ignoreMasked = true;
  const int numNeighbours = 4;
  WorkspaceNearestNeighbourInfo neighbourInfo(workspace, ignoreMasked, numNeighbours);
 
  m_twoThetaLowers.resize(nHistos);
  m_twoThetaUppers.resize(nHistos);
 
  const auto &spectrumInfo = workspace.spectrumInfo();
 
  for (size_t i = 0; i < nHistos; ++i) {
    m_progress->report("Calculating detector angular widths");
 
    // If no detector found, skip onto the next spectrum
    if (!spectrumInfo.hasDetectors(i) || spectrumInfo.isMonitor(i)) {
      continue;
    }
 
    const specnum_t inSpec = workspace.getSpectrum(i).getSpectrumNo();
    const SpectraDistanceMap neighbours = neighbourInfo.getNeighboursExact(inSpec);
 
    // Convert from spectrum numbers to workspace indices
    double thetaWidth = std::numeric_limits<double>::lowest();
 
    // Find theta and phi widths
    const double theta = spectrumInfo.twoTheta(i);
 
    const specnum_t deltaPlus1 = inSpec + 1;
    const specnum_t deltaMinus1 = inSpec - 1;
    const specnum_t deltaPlusT = inSpec + this->m_detNeighbourOffset;
    const specnum_t deltaMinusT = inSpec - this->m_detNeighbourOffset;
 
    for (auto &neighbour : neighbours) {
      specnum_t spec = neighbour.first;
      if (spec == deltaPlus1 || spec == deltaMinus1 || spec == deltaPlusT || spec == deltaMinusT) {
        const double theta_n = spectrumInfo.twoTheta(spec - 1) * 0.5;
 
        const double dTheta = std::abs(theta - theta_n);
        thetaWidth = std::max(thetaWidth, dTheta);
      }
    }
    m_twoThetaLowers[i] = theta - thetaWidth / 2.;
    m_twoThetaUppers[i] = theta + thetaWidth / 2.;
    if (g_log.is(Logger::Priority::PRIO_DEBUG)) {
      g_log.debug() << "Detector at spectrum = " << inSpec << ", width = " << thetaWidth * rad2deg << " degrees\n";
    }
  }
}
 
void SofQWNormalisedPolygon::initAngularCachesTable(const MatrixWorkspace &workspace,
                                                    const TableWorkspace &angleTable) {
  constexpr double skipDetector{-1.};
  const size_t nhist = workspace.getNumberHistograms();
  m_twoThetaLowers = std::vector<double>(nhist, skipDetector);
  m_twoThetaUppers = std::vector<double>(nhist, skipDetector);
  const auto &detIDs = angleTable.getColVector<int>("Detector ID");
  const auto &lowers = angleTable.getColVector<double>("Min two theta");
  const auto &uppers = angleTable.getColVector<double>("Max two theta");
  const auto &spectrumInfo = workspace.spectrumInfo();
  for (size_t i = 0; i < nhist; ++i) {
    m_progress->report("Reading detector angles");
    if (!spectrumInfo.hasDetectors(i) || spectrumInfo.isMonitor(i)) {
      continue;
    }
    const auto &det = spectrumInfo.detector(i);
    try {
      m_EmodeProperties.getEFixed(det);
    } catch (std::runtime_error &) {
      continue;
    }
 
    if (spectrumInfo.hasUniqueDetector(i)) {
      const auto twoThetas = twoThetasFromTable(det.getID(), detIDs, lowers, uppers);
      m_twoThetaLowers[i] = twoThetas.first;
      m_twoThetaUppers[i] = twoThetas.second;
    } else {
      const auto &group = dynamic_cast<const DetectorGroup &>(det);
      const auto ids = group.getDetectorIDs();
      double minTwoTheta{spectrumInfo.twoTheta(i)};
      double maxTwoTheta{minTwoTheta};
      for (const auto id : ids) {
        const auto twoThetas = twoThetasFromTable(id, detIDs, lowers, uppers);
        minTwoTheta = std::min(minTwoTheta, twoThetas.first);
        maxTwoTheta = std::max(maxTwoTheta, twoThetas.second);
      }
      m_twoThetaLowers[i] = minTwoTheta;
      m_twoThetaUppers[i] = maxTwoTheta;
    }
    if (g_log.is(Logger::Priority::PRIO_DEBUG)) {
      g_log.debug() << "Detector at spectrum = " << workspace.getSpectrum(i).getSpectrumNo()
                    << ", lower 2theta = " << m_twoThetaLowers[i] * rad2deg
                    << ", upper 2theta = " << m_twoThetaUppers[i] * rad2deg << " degrees\n";
    }
  }
}
} // namespace Mantid::Algorithms