/// Uniform distribution
inline glm::vec3 getHemispherical(const glm::vec3& n)
{
auto r = getSpherical();
if(glm::dot(r, n) < 0.0)
r = -r;
return r;
}
/**
* A map detector ID and Q ranges
* This method looks unnecessary as it could be calculated on the fly but
* the parallelization means that lazy instantation slows it down due to the
* necessary CRITICAL sections required to update the cache. The Q range
* values are required very frequently so the total time is more than
* offset by this precaching step
*/
DetectorAngularCache initAngularCaches(const MatrixWorkspace *const workspace) {
const size_t nhist = workspace->getNumberHistograms();
std::vector<double> thetas(nhist);
std::vector<double> thetaWidths(nhist);
std::vector<double> detectorHeights(nhist);
auto inst = workspace->getInstrument();
const auto samplePos = inst->getSample()->getPos();
const V3D upDirVec = inst->getReferenceFrame()->vecPointingUp();
for (size_t i = 0; i < nhist; ++i) // signed for OpenMP
{
IDetector_const_sptr det;
try {
det = workspace->getDetector(i);
} catch (Exception::NotFoundError &) {
// Catch if no detector. Next line tests whether this happened - test
// placed
// outside here because Mac Intel compiler doesn't like 'continue' in a
// catch
// in an openmp block.
}
// If no detector found, skip onto the next spectrum
if (!det || det->isMonitor()) {
thetas[i] = -1.0; // Indicates a detector to skip
thetaWidths[i] = -1.0;
continue;
}
// We have to convert theta from radians to degrees
const double theta = workspace->detectorSignedTwoTheta(*det) * rad2deg;
thetas[i] = theta;
/**
* Determine width from shape geometry. A group is assumed to contain
* detectors with the same shape & r, theta value, i.e. a ring mapped-group
* The shape is retrieved and rotated to match the rotation of the detector.
* The angular width is computed using the l2 distance from the sample
*/
if (auto group = boost::dynamic_pointer_cast<const DetectorGroup>(det)) {
// assume they all have same shape and same r,theta
auto dets = group->getDetectors();
det = dets[0];
}
const auto pos = det->getPos() - samplePos;
double l2(0.0), t(0.0), p(0.0);
pos.getSpherical(l2, t, p);
// Get the shape
auto shape =
det->shape(); // Defined in its own reference frame with centre at 0,0,0
BoundingBox bbox = shape->getBoundingBox();
auto maxPoint(bbox.maxPoint());
auto minPoint(bbox.minPoint());
auto span = maxPoint - minPoint;
detectorHeights[i] = span.scalar_prod(upDirVec);
thetaWidths[i] = 2.0 * std::fabs(std::atan((detectorHeights[i] / 2) / l2)) *
180.0 / M_PI;
}
DetectorAngularCache cache;
cache.thetas = thetas;
cache.thetaWidths = thetaWidths;
cache.detectorHeights = detectorHeights;
return cache;
}
