VesuvioCalculateGammaBackground.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 "MantidCurveFitting/Algorithms/VesuvioCalculateGammaBackground.h"
#include "MantidCurveFitting/Algorithms/ConvertToYSpace.h"
#include "MantidCurveFitting/Functions/ComptonProfile.h"
#include "MantidCurveFitting/Functions/VesuvioResolution.h"

#include "MantidAPI/CompositeFunction.h"
#include "MantidAPI/FunctionFactory.h"
#include "MantidAPI/FunctionProperty.h"
#include "MantidAPI/HistogramValidator.h"
#include "MantidAPI/WorkspaceFactory.h"
#include "MantidAPI/WorkspaceUnitValidator.h"

#include "MantidKernel/ArrayProperty.h"
#include "MantidKernel/CompositeValidator.h"

#include "MantidGeometry/Instrument.h"
#include "MantidGeometry/Instrument/ReferenceFrame.h"
#include "MantidGeometry/Objects/BoundingBox.h"
#include "MantidGeometry/Objects/CSGObject.h"

namespace Mantid::CurveFitting::Algorithms {
using namespace API;
using namespace Kernel;
using namespace CurveFitting;
using namespace CurveFitting::Functions;
using namespace std;
using std::placeholders::_1;

// Subscription
DECLARE_ALGORITHM(VesuvioCalculateGammaBackground)

namespace {
/// Number of elements in theta direction integration
size_t NTHETA = 5;
/// Number of elements in up direction integration
size_t NUP = 5;

/// Degrees to radians
double DEG2RAD = M_PI / 180.0;
/// Wavelength of absorption (30603e-24 * 6e19). Constant came from VMS
double ABSORB_WAVELENGTH = 1.83618;
/// Start of forward scattering spectrum numbers (inclusive)
specnum_t FORWARD_SCATTER_SPECMIN = 135;
/// End of forward scattering spectrum numbers (inclusive)
specnum_t FORWARD_SCATTER_SPECMAX = 198;
} // namespace

//--------------------------------------------------------------------------------------------------------
// Public members
//--------------------------------------------------------------------------------------------------------

/// Default constructor
VesuvioCalculateGammaBackground::VesuvioCalculateGammaBackground()
    : Algorithm(), m_inputWS(), m_indices(), m_profileFunction(), m_npeaks(0), m_reversed(), m_samplePos(), m_l1(0.0),
      m_foilRadius(0.0), m_foilUpMin(0.0), m_foilUpMax(0.0), m_foils0(), m_foils1(), m_backgroundWS(), m_correctedWS() {
}

/// Destructor
VesuvioCalculateGammaBackground::~VesuvioCalculateGammaBackground() { m_indices.clear(); }

//--------------------------------------------------------------------------------------------------------
// Private members
//--------------------------------------------------------------------------------------------------------

const std::string VesuvioCalculateGammaBackground::name() const { return "VesuvioCalculateGammaBackground"; }

int VesuvioCalculateGammaBackground::version() const { return 1; }

const std::string VesuvioCalculateGammaBackground::category() const {
  return "CorrectionFunctions\\BackgroundCorrections";
}

void VesuvioCalculateGammaBackground::init() {

  auto wsValidator = std::make_shared<CompositeValidator>();
  wsValidator->add<WorkspaceUnitValidator>("TOF");
  wsValidator->add<HistogramValidator>(false); // point data
  declareProperty(std::make_unique<WorkspaceProperty<>>("InputWorkspace", "", Direction::Input, wsValidator),
                  "An input workspace containing TOF data");

  declareProperty(std::make_unique<API::FunctionProperty>("ComptonFunction", Direction::InOut),
                  "Function that is able to compute the mass spectrum for the input data"
                  "This will usually be the output from the Fitting");

  declareProperty(std::make_unique<ArrayProperty<int>>("WorkspaceIndexList"),
                  "Indices of the spectra to include in the correction. If "
                  "provided, the output only include these spectra\n"
                  "(Default: all spectra from input)");

  declareProperty(std::make_unique<WorkspaceProperty<>>("BackgroundWorkspace", "", Direction::Output),
                  "A new workspace containing the calculated background.");
  declareProperty(std::make_unique<WorkspaceProperty<>>("CorrectedWorkspace", "", Direction::Output),
                  "A new workspace containing the calculated background subtracted from "
                  "the input.");
}

void VesuvioCalculateGammaBackground::exec() {
  retrieveInputs();
  createOutputWorkspaces();

  const auto nhist = static_cast<int64_t>(m_indices.size());
  const int64_t nreports = 10 + nhist * (m_npeaks + 2 * m_foils0.size() * NTHETA * NUP * m_npeaks);
  m_progress = std::make_unique<Progress>(this, 0.0, 1.0, nreports);

  PARALLEL_FOR_IF(Kernel::threadSafe(*m_inputWS, *m_correctedWS, *m_backgroundWS))
  for (int64_t i = 0; i < nhist; ++i) {
    PARALLEL_START_INTERRUPT_REGION
    const size_t outputIndex = i;
    auto indexIter = m_indices.cbegin();
    std::advance(indexIter, i);
    const size_t inputIndex = indexIter->second;

    if (!calculateBackground(inputIndex, outputIndex)) {
      g_log.information("No detector defined for index=" + std::to_string(inputIndex) + ". Skipping correction.");
    }

    PARALLEL_END_INTERRUPT_REGION
  }
  PARALLEL_CHECK_INTERRUPT_REGION

  setProperty("BackgroundWorkspace", m_backgroundWS);
  setProperty("CorrectedWorkspace", m_correctedWS);
}

/**
 * Calculate the background from the input spectrum and assign the value to the
 * output one
 * @param inputIndex The index on the input workspace on which to operate
 * @param outputIndex The index on the output workspace where the results are
 * stored
 * @return True if the background was subtracted, false otherwise
 */
bool VesuvioCalculateGammaBackground::calculateBackground(const size_t inputIndex, const size_t outputIndex) {
  // Copy X values
  m_backgroundWS->setSharedX(outputIndex, m_inputWS->sharedX(inputIndex));
  m_correctedWS->setSharedX(outputIndex, m_inputWS->sharedX(inputIndex));
  // Copy errors to corrected
  m_correctedWS->setSharedE(outputIndex, m_inputWS->sharedE(inputIndex));

  try {
    const auto &inSpec = m_inputWS->getSpectrum(inputIndex);
    const specnum_t spectrumNo(inSpec.getSpectrumNo());
    m_backgroundWS->getSpectrum(outputIndex).copyInfoFrom(inSpec);
    m_correctedWS->getSpectrum(outputIndex).copyInfoFrom(inSpec);

    if (spectrumNo >= FORWARD_SCATTER_SPECMIN && spectrumNo <= FORWARD_SCATTER_SPECMAX) {
      applyCorrection(inputIndex, outputIndex);
    } else {
      g_log.information("Spectrum " + std::to_string(spectrumNo) +
                        " not in forward scatter range. Skipping correction.");
      // Leave background at 0 and just copy data to corrected
      m_correctedWS->setSharedY(outputIndex, m_inputWS->sharedY(inputIndex));
    }
    return true;
  } catch (Exception::NotFoundError &) {
    return false;
  }
}

/**
 * Calculate & apply gamma correction for the given index of the
 * input workspace
 * @param inputIndex A workspace index that defines the input spectrum to
 * correct
 * @param outputIndex A workspace index that defines the output to hold the
 * results
 */
void VesuvioCalculateGammaBackground::applyCorrection(const size_t inputIndex, const size_t outputIndex) {
  m_progress->report("Computing TOF from detector");

  // results go straight in m_correctedWS to save memory allocations
  calculateSpectrumFromDetector(inputIndex, outputIndex);

  m_progress->report("Computing TOF foils");
  // Output goes to m_background to save memory allocations
  calculateBackgroundFromFoils(inputIndex, outputIndex);

  m_progress->report("Computing correction to input");
  // Compute total counts from input data, (detector-foil) contributions
  // assume constant binning
  const size_t nbins = m_correctedWS->blocksize();
  const auto &inY = m_inputWS->y(inputIndex);
  auto &detY = m_correctedWS->mutableY(outputIndex);
  auto &foilY = m_backgroundWS->mutableY(outputIndex);
  const double deltaT = m_correctedWS->x(outputIndex)[1] - m_correctedWS->x(outputIndex)[0];

  double dataCounts(0.0), simulCounts(0.0);
  for (size_t j = 0; j < nbins; ++j) {
    dataCounts += inY[j] * deltaT;
    simulCounts += (detY[j] - foilY[j]) * deltaT;
  }

  // Now corrected for the calculated background
  const double corrFactor = dataCounts / simulCounts;
  if (g_log.is(Logger::Priority::PRIO_INFORMATION))
    g_log.information() << "Correction factor for background=" << corrFactor << "\n";

  for (size_t j = 0; j < nbins; ++j) {
    // m_backgroundWS already contains the foil values, careful not to overwrite
    // them
    double &foilValue = foilY[j]; // non-const reference
    foilValue *= corrFactor;
    detY[j] = (inY[j] - foilValue);
  }
}

/**
 * Results are placed in the mapped index on the output corrected workspace
 * @param inputIndex Workspace index that defines the input spectrum to correct
 * @param outputIndex Workspace index that defines the spectrum to hold the
 * results
 */
void VesuvioCalculateGammaBackground::calculateSpectrumFromDetector(const size_t inputIndex, const size_t outputIndex) {
  // -- Setup detector & resolution parameters --
  DetectorParams detPar = ConvertToYSpace::getDetectorParameters(m_inputWS, inputIndex);
  CurveFitting::Functions::ResolutionParams detRes =
      CurveFitting::Functions::VesuvioResolution::getResolutionParameters(m_inputWS, inputIndex);

  // Compute a time of flight spectrum convolved with a Voigt resolution
  // function for each mass
  // at the detector point & sum to a single spectrum
  auto &ctdet = m_correctedWS->mutableY(outputIndex);
  std::vector<double> tmpWork(ctdet.size());
  ctdet = calculateTofSpectrum(ctdet.rawData(), tmpWork, outputIndex, detPar, detRes);
  // Correct for distance to the detector: 0.5/l2^2
  const double detDistCorr = 0.5 / detPar.l2 / detPar.l2;
  std::transform(ctdet.begin(), ctdet.end(), ctdet.begin(), std::bind(std::multiplies<double>(), _1, detDistCorr));
}

/**
 * Calculate & apply gamma correction for the given index of the
 * input workspace
 * @param inputIndex Workspace index that defines the input spectrum to correct
 * @param outputIndex Workspace index that defines the spectrum to hold the
 * results
 */
void VesuvioCalculateGammaBackground::calculateBackgroundFromFoils(const size_t inputIndex, const size_t outputIndex) {
  // -- Setup detector & resolution parameters --
  DetectorParams detPar = ConvertToYSpace::getDetectorParameters(m_inputWS, inputIndex);
  CurveFitting::Functions::ResolutionParams detRes =
      CurveFitting::Functions::VesuvioResolution::getResolutionParameters(m_inputWS, inputIndex);

  const size_t nxvalues = m_backgroundWS->blocksize();
  std::vector<double> foilSpectrum(nxvalues);
  auto &ctfoil = m_backgroundWS->mutableY(outputIndex);

  // Compute (C1 - C0) where C1 is counts in pos 1 and C0 counts in pos 0
  assert(m_foils0.size() == m_foils1.size());
  for (size_t i = 0; i < m_foils0.size(); ++i) {
    foilSpectrum.assign(nxvalues, 0.0);
    calculateBackgroundSingleFoil(foilSpectrum, outputIndex, m_foils1[i], detPar.pos, detPar, detRes);
    // sum spectrum values from first position
    std::transform(ctfoil.begin(), ctfoil.end(), foilSpectrum.begin(), ctfoil.begin(), std::plus<double>());

    foilSpectrum.assign(nxvalues, 0.0);
    calculateBackgroundSingleFoil(foilSpectrum, outputIndex, m_foils0[i], detPar.pos, detPar, detRes);
    // subtract spectrum values from zeroth position
    std::transform(ctfoil.begin(), ctfoil.end(), foilSpectrum.begin(), ctfoil.begin(), std::minus<double>());
  }
  bool reversed = (m_reversed.count(m_inputWS->getSpectrum(inputIndex).getSpectrumNo()) != 0);
  // This is quicker than the if within the loop
  if (reversed) {
    // The reversed ones should be (C0 - C1)
    std::transform(ctfoil.begin(), ctfoil.end(), ctfoil.begin(), std::bind(std::multiplies<double>(), _1, -1.0));
  }
}

/**
 * Integrates over the foil area defined by the foil radius to accumulate an
 * estimate of the counts
 * resulting from this region
 * @param ctfoil Output vector to hold results
 * @param wsIndex Index on output background workspaces currently operating
 * @param foilInfo Foil description object
 * @param detPos The pre-calculated detector V3D
 * @param detPar DetectorParams object that defines information on the detector
 * associated with spectrum at wsIndex
 * @param detRes ResolutionParams object that defines information on the
 * resolution associated with spectrum at wsIndex
 */
void VesuvioCalculateGammaBackground::calculateBackgroundSingleFoil(std::vector<double> &ctfoil, const size_t wsIndex,
                                                                    const FoilInfo &foilInfo, const V3D &detPos,
                                                                    const DetectorParams &detPar,
                                                                    const ResolutionParams &detRes) {
  /** Integrates over the foils
   *  by dividing into 2cm^2 elements
   *  The integration is performed in cylindrical coordinates
   */

  const double thetaStep = (foilInfo.thetaMax - foilInfo.thetaMin) / static_cast<double>(NTHETA);
  const double thetaStepRad = thetaStep * DEG2RAD;
  const double upStep = (m_foilUpMax - m_foilUpMin) / static_cast<double>(NUP);
  const double elementArea = abs(m_foilRadius * upStep * thetaStepRad);
  V3D elementPos; // reusable vector for computing distances

  // Structs to hold geometry & resolution information
  DetectorParams foilPar = detPar; // copy
  foilPar.t0 = 0.0;
  CurveFitting::Functions::ResolutionParams foilRes = detRes; // copy
  foilRes.dEnGauss = foilInfo.gaussWidth;
  foilRes.dEnLorentz = foilInfo.lorentzWidth;

  const size_t nvalues = ctfoil.size();
  std::vector<double> singleElement(nvalues), tmpWork(nvalues);

  for (size_t i = 0; i < NTHETA; ++i) {
    double thetaZeroRad = (foilInfo.thetaMin + (static_cast<double>(i) + 0.5) * thetaStep) * DEG2RAD;
    elementPos.setZ(m_foilRadius * cos(thetaZeroRad));
    elementPos.setX(m_foilRadius * sin(thetaZeroRad));
    for (size_t j = 0; j < NUP; ++j) {
      double ypos = m_foilUpMin + (static_cast<double>(j) + 0.5) * upStep;
      elementPos.setY(ypos);
      foilPar.l2 = m_samplePos.distance(elementPos);
      foilPar.theta = acos(m_foilRadius * cos(thetaZeroRad) / foilPar.l2); // scattering angle in radians

      // Spectrum for this position
      singleElement.assign(nvalues, 0.0);
      singleElement = calculateTofSpectrum(singleElement, tmpWork, wsIndex, foilPar, foilRes);

      // Correct for absorption & distance
      const double den = (elementPos.Z() * cos(thetaZeroRad) + elementPos.X() * sin(thetaZeroRad));
      const double absorbFactor = 1.0 / (1.0 - exp(-ABSORB_WAVELENGTH * foilPar.l2 / den));
      const double elemDetDist = elementPos.distance(detPos);
      const double distFactor = elementArea / (4.0 * M_PI * foilPar.l2 * foilPar.l2 * elemDetDist * elemDetDist);
      // Add on to other contributions
      for (size_t k = 0; k < nvalues; ++k) {
        ctfoil[k] += singleElement[k] * absorbFactor * distFactor;
      }
    }
  }
}

/**
 * Uses the compton profile functions to compute a particular mass spectrum
 * @param inSpectrum The value of the computed spectrum
 * @param tmpWork Pre-allocated working area that will be overwritten
 * @param wsIndex Index on the output background workspace that gives the X
 * values to use
 * @param detpar Struct containing parameters about the detector
 * @param respar Struct containing parameters about the resolution
 */
std::vector<double> VesuvioCalculateGammaBackground::calculateTofSpectrum(const std::vector<double> &inSpectrum,
                                                                          std::vector<double> &tmpWork,
                                                                          const size_t wsIndex,
                                                                          const DetectorParams &detpar,
                                                                          const ResolutionParams &respar) {
  assert(inSpectrum.size() == tmpWork.size());

  // Assumes the input is in seconds, transform it temporarily
  auto &tseconds = m_backgroundWS->mutableX(wsIndex);
  std::transform(tseconds.begin(), tseconds.end(), tseconds.begin(), std::bind(std::multiplies<double>(), _1, 1e-6));

  // retrieveInputs ensures we will get a composite function and that each
  // member is a ComptonProfile
  // we can't static_cast though due to the virtual inheritance with IFunction
  auto profileFunction =
      std::dynamic_pointer_cast<CompositeFunction>(FunctionFactory::Instance().createInitialized(m_profileFunction));

  std::vector<double> correctedVals(inSpectrum);

  for (size_t i = 0; i < m_npeaks; ++i) {
    auto profile = std::dynamic_pointer_cast<CurveFitting::Functions::ComptonProfile>(profileFunction->getFunction(i));
    profile->disableLogging();
    profile->setUpForFit();

    // Fix the Mass parameter
    profile->fix(0);

    profile->cacheYSpaceValues(m_backgroundWS->points(wsIndex), detpar, respar);

    profile->massProfile(tmpWork.data(), tmpWork.size());
    // Add to final result

    std::transform(correctedVals.begin(), correctedVals.end(), tmpWork.begin(), correctedVals.begin(),
                   std::plus<double>());
    m_progress->report();
  }
  // Put X back microseconds
  std::transform(tseconds.begin(), tseconds.end(), tseconds.begin(), std::bind(std::multiplies<double>(), _1, 1e6));
  return correctedVals;
}

/**
 * Caches input details for the peak information
 */
void VesuvioCalculateGammaBackground::retrieveInputs() {
  m_inputWS = getProperty("InputWorkspace");
  m_profileFunction = getPropertyValue("ComptonFunction");
  if (m_profileFunction.find(';') == std::string::npos) // not composite
  {
    m_profileFunction = "composite=CompositeFunction;" + m_profileFunction;
  }

  IFunction_sptr profileFunction = FunctionFactory::Instance().createInitialized(m_profileFunction);
  if (auto composite = std::dynamic_pointer_cast<CompositeFunction>(profileFunction)) {
    m_npeaks = composite->nFunctions();
    for (size_t i = 0; i < m_npeaks; ++i) {
      auto single = std::dynamic_pointer_cast<CurveFitting::Functions::ComptonProfile>(composite->getFunction(i));
      if (!single) {
        throw std::invalid_argument("Invalid function. Composite must contain "
                                    "only ComptonProfile functions");
      }
    }
  } else {
    throw std::invalid_argument("Invalid function found. Expected ComptonFunction to contain a "
                                "composite of ComptonProfiles or a single ComptonProfile.");
  }

  // Spectrum numbers whose calculation of background from foils is reversed
  m_reversed.clear();
  for (specnum_t i = 143; i < 199; ++i) {
    if ((i >= 143 && i <= 150) || (i >= 159 && i <= 166) || (i >= 175 && i <= 182) || (i >= 191 && i <= 198))
      m_reversed.insert(i);
  }

  // Workspace indices mapping input->output
  m_indices.clear();
  std::vector<int> requestedIndices = getProperty("WorkspaceIndexList");
  if (requestedIndices.empty()) {
    for (size_t i = 0; i < m_inputWS->getNumberHistograms(); ++i) {
      m_indices.emplace(i, i); // 1-to-1
    }
  } else {
    for (size_t i = 0; i < requestedIndices.size(); ++i) {
      m_indices.emplace(i, static_cast<size_t>(requestedIndices[i])); // user-requested->increasing on output
    }
  }

  cacheInstrumentGeometry();
}

/**
 * Create & cache output workspaces
 */
void VesuvioCalculateGammaBackground::createOutputWorkspaces() {
  const size_t nhist = m_indices.size();
  m_backgroundWS = WorkspaceFactory::Instance().create(m_inputWS, nhist);
  m_correctedWS = WorkspaceFactory::Instance().create(m_inputWS, nhist);
}

void VesuvioCalculateGammaBackground::cacheInstrumentGeometry() {
  auto inst = m_inputWS->getInstrument();
  auto refFrame = inst->getReferenceFrame();
  auto upAxis = refFrame->pointingUp();
  auto source = inst->getSource();
  auto sample = inst->getSample();
  m_samplePos = sample->getPos();
  m_l1 = m_samplePos.distance(source->getPos());

  // foils
  auto changer = std::dynamic_pointer_cast<const Geometry::IObjComponent>(inst->getComponentByName("foil-changer"));
  if (!changer) {
    throw std::invalid_argument("Input workspace has no component named foil-changer. "
                                "One is required to define integration area.");
  }

  // 'height' of box sets limits in beam direction
  Geometry::BoundingBox boundBox;
  changer->getBoundingBox(boundBox);
  m_foilUpMin = boundBox.minPoint()[upAxis];
  m_foilUpMax = boundBox.maxPoint()[upAxis];

  // foil geometry
  // there should be the same number in each position
  const auto &pmap = m_inputWS->constInstrumentParameters();
  auto foils0 = inst->getAllComponentsWithName("foil-pos0");
  auto foils1 = inst->getAllComponentsWithName("foil-pos1");
  const size_t nfoils = foils0.size();
  if (nfoils != foils1.size()) {
    std::ostringstream os;
    os << "Mismatch in number of foils between pos 0 & 1: pos0=" << nfoils << ", pos1=" << foils1.size();
    throw std::runtime_error(os.str());
  }
  // It is assumed that the foils all lie on a circle of the same radius from
  // the sample position
  auto firstFoilPos = foils0[0]->getPos();
  double dummy(0.0);
  firstFoilPos.getSpherical(m_foilRadius, dummy, dummy);

  // Cache min/max theta values
  m_foils0.resize(nfoils);
  m_foils1.resize(nfoils);
  for (size_t i = 0; i < nfoils; ++i) {
    const auto &foil0 = foils0[i];
    auto thetaRng0 = calculateThetaRange(foil0, m_foilRadius, refFrame->pointingHorizontal());
    FoilInfo descr;
    descr.thetaMin = thetaRng0.first;
    descr.thetaMax = thetaRng0.second;
    descr.lorentzWidth = ConvertToYSpace::getComponentParameter(*foil0, pmap, "hwhm_lorentz");
    descr.gaussWidth = ConvertToYSpace::getComponentParameter(*foil0, pmap, "sigma_gauss");
    m_foils0[i] = descr; // copy

    const auto &foil1 = foils1[i];
    auto thetaRng1 = calculateThetaRange(foil1, m_foilRadius, refFrame->pointingHorizontal());
    descr.thetaMin = thetaRng1.first;
    descr.thetaMax = thetaRng1.second;
    descr.lorentzWidth = ConvertToYSpace::getComponentParameter(*foil1, pmap, "hwhm_lorentz");
    descr.gaussWidth = ConvertToYSpace::getComponentParameter(*foil1, pmap, "sigma_gauss");
    m_foils1[i] = descr; // copy
  }

  if (g_log.is(Kernel::Logger::Priority::PRIO_INFORMATION)) {
    std::ostringstream os;
    os << "Instrument geometry:\n"
       << "  l1 = " << m_l1 << "m\n"
       << "  foil radius = " << m_foilRadius << "\n"
       << "  foil integration min = " << m_foilUpMin << "\n"
       << "  foil integration max = " << m_foilUpMax << "\n";
    std::ostringstream secondos;
    for (size_t i = 0; i < nfoils; ++i) {
      const auto &descr0 = m_foils0[i];
      os << "  foil theta range in position 0: theta_min=" << descr0.thetaMin << ", theta_max=" << descr0.thetaMax
         << "\n";
      const auto &descr1 = m_foils1[i];
      secondos << "  foil theta range in position 1: theta_min=" << descr1.thetaMin << ", theta_max=" << descr1.thetaMax
               << "\n";
    }
    g_log.information() << os.str() << secondos.str();
  }
}

/**
 * @param foilComp A pointer to the foil component
 * @param radius The radius that gives the distance to the centre of the
 * bounding box
 * @param horizDir An enumeration defining which direction is horizontal
 * @return The min/max angle in theta(degrees) (horizontal direction if you
 * assume mid-point theta = 0)
 */
std::pair<double, double>
VesuvioCalculateGammaBackground::calculateThetaRange(const Geometry::IComponent_const_sptr &foilComp,
                                                     const double radius, const unsigned int horizDir) const {
  auto shapedObject = std::dynamic_pointer_cast<const Geometry::IObjComponent>(foilComp);
  if (!shapedObject) {
    throw std::invalid_argument("A foil has been defined without a shape. "
                                "Please check instrument definition.");
  }

  // First get current theta position
  auto pos = foilComp->getPos();
  double theta(0.0), dummy(0.0);
  pos.getSpherical(dummy, theta, dummy); // absolute angle values
  if (pos[horizDir] < 0.0)
    theta *= -1.0; // negative quadrant for theta

  // Compute dtheta from bounding box & radius
  const auto &box = shapedObject->shape()->getBoundingBox();
  // box has center at 0,0,0
  double xmax = box.maxPoint()[0];
  double dtheta = std::asin(xmax / radius) * 180.0 / M_PI; // degrees
  return std::make_pair(theta - dtheta, theta + dtheta);
}

} // namespace Mantid::CurveFitting::Algorithms