MCInteractionVolume.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/SampleCorrections/MCInteractionVolume.h"
#include "MantidAPI/Sample.h"
#include "MantidGeometry/Instrument/SampleEnvironment.h"
#include "MantidGeometry/Objects/CSGObject.h"
#include "MantidGeometry/Objects/Track.h"
#include "MantidKernel/PseudoRandomNumberGenerator.h"
#include <iomanip>
 
namespace Mantid {
using Geometry::Track;
using Kernel::V3D;
 
namespace Algorithms {
 
MCInteractionVolume::MCInteractionVolume(const API::Sample &sample, const size_t maxScatterAttempts,
                                         const MCInteractionVolume::ScatteringPointVicinity pointsIn)
    : m_sample(sample.getShape().clone()), m_env(nullptr), m_activeRegion(getFullBoundingBox()),
      m_maxScatterAttempts(maxScatterAttempts), m_pointsIn(pointsIn) {
  try {
    m_env = &sample.getEnvironment();
    assert(m_env);
    if (m_env->nelements() == 0) {
      throw std::invalid_argument("MCInteractionVolume() - Sample enviroment has zero components.");
    }
  } catch (std::runtime_error &) {
    // swallow this as no defined environment from getEnvironment
  }
 
  bool atLeastOneValidShape = m_sample->hasValidShape();
  if (!atLeastOneValidShape && m_env) {
    for (size_t i = 0; i < m_env->nelements(); i++) {
      if (m_env->getComponent(i).hasValidShape()) {
        atLeastOneValidShape = true;
        break;
      }
    }
  }
  if (!atLeastOneValidShape) {
    throw std::invalid_argument("MCInteractionVolume() - Either the Sample or one of the "
                                "environment parts must have a valid shape.");
  }
}
 
const Geometry::BoundingBox MCInteractionVolume::getFullBoundingBox() const {
  auto sampleBox = m_sample->getBoundingBox();
  if (m_pointsIn != ScatteringPointVicinity::SAMPLEONLY && m_env) {
    const auto &envBox = m_env->boundingBox();
    sampleBox.grow(envBox);
  }
  return sampleBox;
}
 
void MCInteractionVolume::setActiveRegion(const Geometry::BoundingBox &region) { m_activeRegion = region; }
 
int MCInteractionVolume::getComponentIndex(Kernel::PseudoRandomNumberGenerator &rng) const {
  // the sample has componentIndex -1, env components are number 0 upwards
  const int sampleIndex = -1;
  const int firstEnvIndex = sampleIndex + 1;
  int startIndex = sampleIndex;
  int endIndex = m_env ? static_cast<int>(m_env->nelements()) - 1 : sampleIndex;
  if ((m_pointsIn == ScatteringPointVicinity::ENVIRONMENTONLY) || !m_sample->hasValidShape())
    startIndex = firstEnvIndex;
  if (m_pointsIn == ScatteringPointVicinity::SAMPLEONLY)
    endIndex = sampleIndex;
  if (startIndex == endIndex) {
    return startIndex;
  } else {
    return rng.nextInt(startIndex, endIndex);
  }
}
 
boost::optional<Kernel::V3D>
MCInteractionVolume::generatePointInObjectByIndex(int componentIndex, Kernel::PseudoRandomNumberGenerator &rng) const {
  boost::optional<Kernel::V3D> pointGenerated{boost::none};
  if (componentIndex == -1) {
    pointGenerated = m_sample->generatePointInObject(rng, m_activeRegion, 1);
  } else {
    pointGenerated = m_env->getComponent(componentIndex).generatePointInObject(rng, m_activeRegion, 1);
  }
  return pointGenerated;
}
 
ComponentScatterPoint MCInteractionVolume::generatePoint(Kernel::PseudoRandomNumberGenerator &rng) const {
  for (size_t i = 0; i < m_maxScatterAttempts; i++) {
    int componentIndex = getComponentIndex(rng);
    boost::optional<Kernel::V3D> pointGenerated = generatePointInObjectByIndex(componentIndex, rng);
    if (pointGenerated) {
      return {componentIndex, *pointGenerated};
    }
  }
  throw std::runtime_error("MCInteractionVolume::generatePoint() - Unable to "
                           "generate point in object after " +
                           std::to_string(m_maxScatterAttempts) + " attempts");
}
 
TrackPair MCInteractionVolume::calculateBeforeAfterTrack(Kernel::PseudoRandomNumberGenerator &rng,
                                                         const Kernel::V3D &startPos, const Kernel::V3D &endPos,
                                                         MCInteractionStatistics &stats) const {
  // Generate scatter point. If there is an environment present then
  // first select whether the scattering occurs on the sample or the
  // environment. The attenuation for the path leading to the scatter point
  // is calculated in reverse, i.e. defining the track from the scatter pt
  // backwards for simplicity with how the Track object works. This avoids
  // having to understand exactly which object the scattering occurred in.
  ComponentScatterPoint scatterPos;
 
  scatterPos = generatePoint(rng);
  stats.UpdateScatterPointCounts(scatterPos.componentIndex, false);
 
  const auto toStart = normalize(startPos - scatterPos.scatterPoint);
  auto beforeScatter = std::make_shared<Track>(scatterPos.scatterPoint, toStart);
  int nlinks = m_sample->interceptSurface(*beforeScatter);
  if (m_env) {
    nlinks += m_env->interceptSurfaces(*beforeScatter);
  }
  // This should not happen but numerical precision means that it can
  // occasionally occur with tracks that are very close to the surface
  if (nlinks == 0) {
    return {false, nullptr, nullptr};
  }
  stats.UpdateScatterPointCounts(scatterPos.componentIndex, true);
 
  // Now track to final destination
  const V3D scatteredDirec = normalize(endPos - scatterPos.scatterPoint);
  auto afterScatter = std::make_shared<Track>(scatterPos.scatterPoint, scatteredDirec);
  m_sample->interceptSurface(*afterScatter);
  if (m_env) {
    m_env->interceptSurfaces(*afterScatter);
  }
  stats.UpdateScatterAngleStats(toStart, scatteredDirec);
  return {true, beforeScatter, afterScatter};
}
 
} // namespace Algorithms
} // namespace Mantid