/**
* Generate a random point within the beam profile using the supplied random
* number source
* @param rng A reference to a random number generator
* @return An IBeamProfile::Ray describing the start and direction
*/
IBeamProfile::Ray RectangularBeamProfile::generatePoint(
Kernel::PseudoRandomNumberGenerator &rng) const {
V3D pt;
pt[m_upIdx] = m_min[m_upIdx] + rng.nextValue() * m_height;
pt[m_horIdx] = m_min[m_horIdx] + rng.nextValue() * m_width;
pt[m_beamIdx] = m_min[m_beamIdx];
return {pt, m_beamDir};
}
/**
* Return a random point in a cuboid shape.
* @param shapeInfo cuboid's shape info
* @param rng a random number generate
* @return a random point inside the cuboid
*/
Kernel::V3D inCuboid(const detail::ShapeInfo &shapeInfo,
Kernel::PseudoRandomNumberGenerator &rng) {
const auto geometry = shapeInfo.cuboidGeometry();
const double r1{rng.nextValue()};
const double r2{rng.nextValue()};
const double r3{rng.nextValue()};
const Kernel::V3D basis1{geometry.leftFrontTop - geometry.leftFrontBottom};
const Kernel::V3D basis2{geometry.leftBackBottom - geometry.leftFrontBottom};
const Kernel::V3D basis3{geometry.rightFrontBottom -
geometry.leftFrontBottom};
return geometry.leftFrontBottom + (basis1 * r1 + basis2 * r2 + basis3 * r3);
}
/**
* Return a random point in cylinder.
* @param shapeInfo cylinder's shape info
* @param rng a random number generator
* @return a point
*/
Kernel::V3D inCylinder(const detail::ShapeInfo &shapeInfo,
Kernel::PseudoRandomNumberGenerator &rng) {
const auto geometry = shapeInfo.cylinderGeometry();
const double r1{rng.nextValue()};
const double r2{rng.nextValue()};
const double r3{rng.nextValue()};
const double polar{2. * M_PI * r1};
// The sqrt is needed for a uniform distribution of points.
const double r{geometry.radius * std::sqrt(r2)};
const double z{geometry.height * r3};
const Kernel::V3D alongAxis{geometry.axis * z};
auto localPoint = localPointInCylinder(geometry.axis, alongAxis, polar, r);
return localPoint + geometry.centreOfBottomBase;
}
/**
* Return a random point in sphere.
* @param shapeInfo sphere's shape info
* @param rng a random number generator
* @return a point
*/
Kernel::V3D inSphere(const detail::ShapeInfo &shapeInfo,
Kernel::PseudoRandomNumberGenerator &rng) {
const auto geometry = shapeInfo.sphereGeometry();
const double r1{rng.nextValue()};
const double r2{rng.nextValue()};
const double r3{rng.nextValue()};
const double azimuthal{2. * M_PI * r1};
// The acos is needed for a uniform distribution of points.
const double polar{std::acos(2. * r2 - 1.)};
const double r{r3 * geometry.radius};
const double x{r * std::cos(azimuthal) * std::sin(polar)};
const double y{r * std::sin(azimuthal) * std::sin(polar)};
const double z{r * std::cos(polar)};
return geometry.centre + Kernel::V3D{x, y, z};
}
/**
* Return a random point in a hollow cylinder
* @param shapeInfo hollow cylinder's shape info
* @param rng a random number generator
* @return a point
*/
Kernel::V3D inHollowCylinder(const detail::ShapeInfo &shapeInfo,
Kernel::PseudoRandomNumberGenerator &rng) {
const auto geometry = shapeInfo.hollowCylinderGeometry();
const double r1{rng.nextValue()};
const double r2{rng.nextValue()};
const double r3{rng.nextValue()};
const double polar{2. * M_PI * r1};
// We need a random number between the inner radius and outer radius, but also
// need the square root for a uniform distribution of points
const double c1 = geometry.innerRadius * geometry.innerRadius;
const double c2 = geometry.radius * geometry.radius;
const double r{std::sqrt(c1 + (c2 - c1) * r2)};
const double z{geometry.height * r3};
const Kernel::V3D alongAxis{geometry.axis * z};
auto localPoint = localPointInCylinder(geometry.axis, alongAxis, polar, r);
return localPoint + geometry.centreOfBottomBase;
}
/**
* Calculate the attenuation correction factor the volume given a start and
* end point.
* @param rng A reference to a PseudoRandomNumberGenerator producing
* random number between [0,1]
* @param startPos Origin of the initial track
* @param endPos Final position of neutron after scattering (assumed to be
* outside of the "volume")
* @param lambdaBefore Wavelength, in \f$\\A^-1\f$, before scattering
* @param lambdaAfter Wavelength, in \f$\\A^-1\f$, after scattering
* @return The fraction of the beam that has been attenuated. A negative number
* indicates the track was not valid.
*/
double MCInteractionVolume::calculateAbsorption(
Kernel::PseudoRandomNumberGenerator &rng, const Kernel::V3D &startPos,
const Kernel::V3D &endPos, double lambdaBefore, double lambdaAfter) 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.
V3D scatterPos;
if (m_env && (rng.nextValue() > 0.5)) {
scatterPos =
m_env->generatePoint(rng, m_activeRegion, MAX_SCATTER_ATTEMPTS);
} else {
scatterPos = m_sample.generatePointInObject(rng, m_activeRegion,
MAX_SCATTER_ATTEMPTS);
}
auto toStart = startPos - scatterPos;
toStart.normalize();
Track beforeScatter(scatterPos, 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 -1.0;
}
// Function to calculate total attenuation for a track
auto calculateAttenuation = [](const Track &path, double lambda) {
double factor(1.0);
for (const auto &segment : path) {
const double length = segment.distInsideObject;
const auto &segObj = *(segment.object);
const auto &segMat = segObj.material();
factor *= attenuation(segMat.numberDensity(),
segMat.totalScatterXSection(lambda) +
segMat.absorbXSection(lambda),
length);
}
return factor;
};
// Now track to final destination
V3D scatteredDirec = endPos - scatterPos;
scatteredDirec.normalize();
Track afterScatter(scatterPos, scatteredDirec);
m_sample.interceptSurface(afterScatter);
if (m_env) {
m_env->interceptSurfaces(afterScatter);
}
return calculateAttenuation(beforeScatter, lambdaBefore) *
calculateAttenuation(afterScatter, lambdaAfter);
}
/**
* Return a random point in a generic shape limited by a bounding box.
* @param object an object in which the point is generated
* @param rng a random number generator
* @param box a box restricting the point's volume
* @param maxAttempts number of attempts to find a suitable point
* @return a point or none if maxAttempts was exceeded
*/
boost::optional<Kernel::V3D> bounded(const IObject &object,
Kernel::PseudoRandomNumberGenerator &rng,
const BoundingBox &box,
size_t maxAttempts) {
boost::optional<Kernel::V3D> point{boost::none};
if (box.isNull()) {
throw std::invalid_argument(
"Invalid bounding box. Cannot generate random point.");
}
for (size_t attempts{0}; attempts < maxAttempts; ++attempts) {
const double r1 = rng.nextValue();
const double r2 = rng.nextValue();
const double r3 = rng.nextValue();
auto pt = box.generatePointInside(r1, r2, r3);
if (object.isValid(pt)) {
point = pt;
break;
}
};
return point;
}