PhotonVoxels.cxx

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// library header
#include "larsim/Simulation/PhotonVoxels.h"
#include "larcorealg/Geometry/geo_vectors_utils.h"

// C++ standard libraries
#include <algorithm> // std::min(), std::max()
#include <cmath>     // std::abs(), std::floor()
#include <stdexcept> // std::runtime_error
#include <string>

namespace sim {

  //----------------------------------------------------------------------------
  // PhotonVoxelDef class
  //----------------------------------------------------------------------------
  PhotonVoxelDef::PhotonVoxelDef(double xMin,
                                 double xMax,
                                 int xN,
                                 double yMin,
                                 double yMax,
                                 int yN,
                                 double zMin,
                                 double zMax,
                                 int zN)
    : fLowerCorner(xMin, yMin, zMin)
    , fUpperCorner(xMax, yMax, zMax)
    , fxSteps(xN)
    , fySteps(yN)
    , fzSteps(zN)
  {}

  //----------------------------------------------------------------------------
  std::array<unsigned int, 3U> PhotonVoxelDef::GetSteps() const
  {
    // BUG the double brace syntax is required to work around clang bug 21629
    // (https://bugs.llvm.org/show_bug.cgi?id=21629)
    return {{fxSteps, fySteps, fzSteps}};
  }

  //----------------------------------------------------------------------------
  bool PhotonVoxelDef::operator==(const PhotonVoxelDef& right) const
  {
    return ((GetRegionUpperCorner() == right.GetRegionUpperCorner()) &&
            (GetRegionLowerCorner() == right.GetRegionLowerCorner()) &&
            (GetSteps() == right.GetSteps()));
  }

  //----------------------------------------------------------------------------
  unsigned int PhotonVoxelDef::GetNVoxels() const
  {
    return fxSteps * fySteps * fzSteps;
  }

  //----------------------------------------------------------------------------
  int PhotonVoxelDef::GetVoxelID(double const* Position) const
  {
    return GetVoxelIDImpl(geo::vect::makeFromCoords<geo::Point_t>(Position));
  }

  //----------------------------------------------------------------------------
  std::optional<std::array<sim::PhotonVoxelDef::NeiInfo, 8U>>
  PhotonVoxelDef::GetNeighboringVoxelIDsImpl(geo::Point_t const& v) const
  {
    if (!isInside(v)) return {};

    std::array<sim::PhotonVoxelDef::NeiInfo, 8U> ret;

    // Position in voxel coordinates including floating point part
    auto const rStepD = GetVoxelStepCoordsUnchecked(v);

    // The neighbours are the 8 corners of a cube around this point
    std::size_t iNeigh = 0U;
    for (int dx : {0, 1}) {
      for (int dy : {0, 1}) {
        for (int dz : {0, 1}) {
          // The full 3D step
          const int dr[3] = {dx, dy, dz};

          // The integer-only position of the current corner
          int rStepI[3];
          for (int d = 0; d < 3; ++d) {
            // Round down to get the "lower left" corner
            rStepI[d] = int(rStepD[d]);
            // Ensure we'll stay in-bounds
            rStepI[d] = std::max(0, rStepI[d]);
            rStepI[d] = std::min(rStepI[d], int(GetSteps()[d]) - 2);
            // Adjust to the corner we're actually considering
            rStepI[d] += dr[d];
          }

          double w = 1;
          for (int d = 0; d < 3; ++d) {
            // These expressions will interpolate when between the 8 corners,
            // and extrapolate in the half-voxel space around the edges.
            if (dr[d] == 0)
              w *= 1 + rStepI[d] - rStepD[d];
            else
              w *= 1 - rStepI[d] + rStepD[d];
          }

          const int id = (rStepI[0] + rStepI[1] * (fxSteps) + rStepI[2] * (fxSteps * fySteps));

          ret[iNeigh++] = {id, w};
        }
      }
    }

    // Sanity check the weights sum to 1
    double wSum = 0;
    for (const NeiInfo& n : ret)
      wSum += n.weight;
    if (std::abs(wSum - 1) > 1e-3) {
      std::string msg = "PhotonVoxelDef::GetNeighboringVoxelIDs():"
                        " Weights sum to " +
                        std::to_string(wSum) +
                        " (should be 1)."
                        " Weights are:";
      for (const NeiInfo& n : ret) {
        msg += ' ';
        msg += std::to_string(n.weight);
      }
      throw std::runtime_error(msg);
    }
    return {ret};
  }

  //----------------------------------------------------------------------------
  PhotonVoxel PhotonVoxelDef::GetPhotonVoxel(int ID) const
  {
    //    float TempID = (float) ID;

    // Decompose ID into steps in each direction
    int xStep = ID % fxSteps;
    int yStep = ((ID - xStep) / fxSteps) % fySteps;
    int zStep = ((ID - xStep - (yStep * fxSteps)) / (fySteps * fxSteps)) % fzSteps;

    auto const VoxelSize = GetVoxelSize<geo::Vector_t>();

    double const xMin = VoxelSize.X() * (xStep) + fLowerCorner.X();
    double const xMax = VoxelSize.X() * (xStep + 1) + fLowerCorner.X();
    double const yMin = VoxelSize.Y() * (yStep) + fLowerCorner.Y();
    double const yMax = VoxelSize.Y() * (yStep + 1) + fLowerCorner.Y();
    double const zMin = VoxelSize.Z() * (zStep) + fLowerCorner.Z();
    double const zMax = VoxelSize.Z() * (zStep + 1) + fLowerCorner.Z();

    return PhotonVoxel(xMin, xMax, yMin, yMax, zMin, zMax);
  }

  //----------------------------------------------------------------------------
  bool PhotonVoxelDef::IsLegalVoxelID(int ID) const
  {
    return ((ID >= 0) && (static_cast<unsigned int>(ID) < GetNVoxels()));
  }

  std::array<int, 3U> PhotonVoxelDef::GetVoxelCoords(int ID) const
  {
    std::array<int, 3U> ReturnVector;
    ReturnVector[0] = ID % fxSteps;
    ReturnVector[1] = ((ID - ReturnVector[0]) / fxSteps) % fySteps;
    ReturnVector[2] =
      ((ID - ReturnVector[0] - (ReturnVector[1] * fxSteps)) / (fySteps * fxSteps)) % fzSteps;
    return ReturnVector;
  }

  //----------------------------------------------------------------------------
  std::array<double, 3U> PhotonVoxelDef::GetVoxelStepCoordsUnchecked(geo::Point_t const& p) const
  {

    auto const span = fUpperCorner - fLowerCorner;
    auto const relPos = p - fLowerCorner;

    // BUG the double brace syntax is required to work around clang bug 21629
    // (https://bugs.llvm.org/show_bug.cgi?id=21629)
    return {{(relPos.X() / span.X()) * fxSteps,
             (relPos.Y() / span.Y()) * fySteps,
             (relPos.Z() / span.Z()) * fzSteps}};
  } // PhotonVoxelDef::GetVoxelStepCoordsUnchecked()

  //----------------------------------------------------------------------------
  int PhotonVoxelDef::GetVoxelIDImpl(geo::Point_t const& p) const
  {
    if (!isInside(p)) return -1;

    auto const stepCoords = GetVoxelStepCoordsUnchecked(p);

    // figure out how many steps this point is in the x,y,z directions;
    // `p` is guaranteed to be in the mapped volume by the previous check
    int xStep = static_cast<int>(stepCoords[0]);
    int yStep = static_cast<int>(stepCoords[1]);
    int zStep = static_cast<int>(stepCoords[2]);

    // if within bounds, generate the voxel ID
    return (xStep + yStep * (fxSteps) + zStep * (fxSteps * fySteps));
  }

  //----------------------------------------------------------------------------
  bool PhotonVoxelDef::isInsideVolume(geo::Point_t const& point,
                                      geo::Point_t const& lower,
                                      geo::Point_t const& upper)
  {
    return isInsideRange(point.X(), lower.X(), upper.X()) &&
           isInsideRange(point.Y(), lower.Y(), upper.Y()) &&
           isInsideRange(point.Z(), lower.Z(), upper.Z());
  }

  bool PhotonVoxelDef::isInsideRange(double value, double lower, double upper)
  {

    return (value >= lower) && (value < upper);

  } // PhotonVoxelDef::isInsideRange()

  //----------------------------------------------------------------------------

  std::ostream& operator<<(std::ostream& out, sim::PhotonVoxelDef const& voxelDef)
  {

    auto const& lower = voxelDef.GetRegionLowerCorner();
    auto const& upper = voxelDef.GetRegionUpperCorner();
    auto const& steps = voxelDef.GetSteps();
    auto const& stepSize = voxelDef.GetVoxelSize();

    out << "Volume " << voxelDef.GetVolumeSize() << " cm^3 split in " << voxelDef.GetNVoxels()
        << " voxels:"
        << "\n  - x axis: [ " << lower.X() << " ; " << upper.X() << " ] split in " << steps[0]
        << "x " << stepSize.X() << " cm steps"
        << "\n  - y axis: [ " << lower.Y() << " ; " << upper.Y() << " ] split in " << steps[1]
        << "x " << stepSize.Y() << " cm steps"
        << "\n  - z axis: [ " << lower.Z() << " ; " << upper.Z() << " ] split in " << steps[2]
        << "x " << stepSize.Z() << " cm steps"
        << "\n";

    return out;
  } // operator<< (sim::PhotonVoxelDef)

  //----------------------------------------------------------------------------

} // namespace sim