Added field interpolators and test case to field module

src/field/interpolators/FieldInterpolatorCreators.h

+//======================================================================================================================
+//
+//  This file is part of waLBerla. waLBerla is free software: you can 
+//  redistribute it and/or modify it under the terms of the GNU General Public
+//  License as published by the Free Software Foundation, either version 3 of 
+//  the License, or (at your option) any later version.
+//  
+//  waLBerla is distributed in the hope that it will be useful, but WITHOUT 
+//  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 
+//  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License 
+//  for more details.
+//  
+//  You should have received a copy of the GNU General Public License along
+//  with waLBerla (see COPYING.txt). If not, see <http://www.gnu.org/licenses/>.
+//
+//! \file FieldInterpolatorCreators.h
+//! \ingroup field
+//! \author Christoph Rettinger <christoph.rettinger@fau.de>
+//
+//======================================================================================================================
+
+#pragma once
+
+#include "core/DataTypes.h"
+#include "core/Set.h"
+
+#include "blockforest/BlockDataHandling.h"
+
+#include "domain_decomposition/StructuredBlockStorage.h"
+
+namespace walberla {
+namespace field {
+
+//**********************************************************************************************************************
+/*! FieldInterpolatorCreators
+ *
+ * \ingroup field
+ *
+ * Interpolator_T: A field interpolator that has a constructor
+ *  ( const shared_ptr<StructuredBlockStorage> & blockStorage, const IBlock & block, const BaseField_T & baseField,
+ *    const FlagField_T & flagField, const flag_t & evaluationMask )
+ * and getter functions:
+ *  template< typename ForwardIterator_T > inline void get( const Vector3<real_t> & position, ForwardIterator_T interpolationResultBegin )
+ *  template< typename ForwardIterator_T > inline void get( const real_t & x, const real_t & y, const real_t & z, ForwardIterator_T interpolationResultBegin )
+ *
+ * See TrilinearFieldInterpolator for an example implementation.
+ *
+ * A field interpolator is aware of the flag field (FlagField_T) and uses only values that contain flags from a given mask.
+ *
+ * Field Interpolators can be used to sample the underlying field at certain positions.
+ * E.g. the fluid velocity can be interpolated to a desired global position from a velocity field.
+ *
+ */
+//**********************************************************************************************************************
+template< typename Interpolator_T, typename FlagField_T >
+class InterpolatorHandling : public blockforest::AlwaysInitializeBlockDataHandling< Interpolator_T >
+{
+public:
+
+   InterpolatorHandling( const shared_ptr<StructuredBlockStorage> & blockStorage,
+                         const ConstBlockDataID & interpolatedFieldID,
+                         const ConstBlockDataID & flagFieldID,
+                         const Set< FlagUID > & cellsToEvaluate ) :
+   blockStorage_( blockStorage ), interpolatedFieldID_( interpolatedFieldID ), flagFieldID_( flagFieldID ), cellsToEvaluate_( cellsToEvaluate )
+   {}
+
+   Interpolator_T * initialize( IBlock * const block )
+   {
+      typedef typename Interpolator_T::BaseField_T InterpolatedField_T;
+      typedef typename FlagField_T::flag_t flag_t;
+      const InterpolatedField_T * interpolatedField = block->getData< InterpolatedField_T >( interpolatedFieldID_ );
+      const FlagField_T * flagField = block->getData< FlagField_T >( flagFieldID_ );
+
+      WALBERLA_ASSERT_NOT_NULLPTR( interpolatedField );
+      WALBERLA_ASSERT_NOT_NULLPTR( flagField );
+
+      const flag_t evaluationMask = flagField->getMask( cellsToEvaluate_ );
+
+      return new Interpolator_T( blockStorage_, *block, *interpolatedField, *flagField, evaluationMask );
+   }
+
+private:
+
+   shared_ptr<StructuredBlockStorage> blockStorage_;
+   ConstBlockDataID interpolatedFieldID_;
+   ConstBlockDataID flagFieldID_;
+   Set< FlagUID > cellsToEvaluate_;
+   
+}; // class InterpolatorHandling
+
+
+
+template< typename Interpolator_T, typename FlagField_T  >
+inline BlockDataID addFieldInterpolator( const shared_ptr< StructuredBlockStorage > & blocks,
+                                         const ConstBlockDataID & interpolatedFieldID,
+                                         const ConstBlockDataID & flagFieldID,
+                                         const Set< FlagUID > & cellsToEvaluate,
+                                         const std::string & identifier = std::string(),
+                                         const Set<SUID> & requiredSelectors     = Set<SUID>::emptySet(),
+                                         const Set<SUID> & incompatibleSelectors = Set<SUID>::emptySet() )
+{
+   return blocks->addBlockData( make_shared< InterpolatorHandling< Interpolator_T, FlagField_T > >( blocks, interpolatedFieldID, flagFieldID, cellsToEvaluate ), identifier, requiredSelectors, incompatibleSelectors );
+}
+
+
+} // namespace field
+} // namespace walberla

src/field/interpolators/KernelFieldInterpolator.h

+//======================================================================================================================
+//
+//  This file is part of waLBerla. waLBerla is free software: you can
+//  redistribute it and/or modify it under the terms of the GNU General Public
+//  License as published by the Free Software Foundation, either version 3 of
+//  the License, or (at your option) any later version.
+//
+//  waLBerla is distributed in the hope that it will be useful, but WITHOUT
+//  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+//  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+//  for more details.
+//
+//  You should have received a copy of the GNU General Public License along
+//  with waLBerla (see COPYING.txt). If not, see <http://www.gnu.org/licenses/>.
+//
+//! \file KernelFieldInterpolator.h
+//! \ingroup field
+//! \author Christoph Rettinger <christoph.rettinger@fau.de>
+//
+//======================================================================================================================
+
+#pragma once
+
+#include "core/debug/Debug.h"
+#include "core/math/Vector3.h"
+
+#include "domain_decomposition/StructuredBlockStorage.h"
+
+#include "field/FlagField.h"
+
+#include "stencil/D3Q27.h"
+
+#include <numeric>
+
+namespace walberla {
+namespace field {
+
+namespace kernelweights
+{
+
+// corresponds to the smoothed dirac delta function from Roma et al - An Adaptive Version of the Immersed Boundary Method
+// f(r) != 0 for abs(r) < 1.5 -> requires three neighborhood cells
+real_t smoothedDeltaFunction( const real_t & r )
+{
+   real_t rAbs = std::fabs(r);
+   if( rAbs <= real_t(0.5) )
+   {
+      return (real_t(1) + std::sqrt( - real_t(3) * r * r + real_t(1) ) ) * (real_t(1) / real_t(3));
+   } else if ( rAbs < real_t(1.5) )
+   {
+      return (real_t(5) - real_t(3) * rAbs - std::sqrt( - real_t(3) * ( real_t(1) - rAbs ) * ( real_t(1) - rAbs ) + real_t(1) ) ) * ( real_t(1) / real_t(6) );
+   } else
+   {
+      return real_t(0);
+   }
+
+}
+
+// X: Lagrangian position, x: Eulerian position (usually cell center), global coordinates
+// dx, dy, dz: mesh spacing
+real_t kernelWeightFunction( const real_t & X, const real_t & Y, const real_t & Z,
+                             const real_t & x, const real_t & y, const real_t & z,
+                             const real_t & dx = real_t(1), const real_t & dy = real_t(1), const real_t & dz = real_t(1) )
+{
+   return smoothedDeltaFunction( ( X - x ) / dx ) * smoothedDeltaFunction( ( Y - y ) / dy ) * smoothedDeltaFunction( ( Z - z ) / dz );
+}
+
+// X: Lagrangian position, x: Eulerian position (usually cell center), global coordinates
+// dx, dy, dz: mesh spacing
+real_t kernelWeightFunction( const Vector3<real_t> & X, const Vector3<real_t> & x,
+                             const real_t & dx = real_t(1), const real_t & dy = real_t(1), const real_t & dz = real_t(1) )
+{
+   return smoothedDeltaFunction( ( X[0] - x[0] ) / dx ) * smoothedDeltaFunction( ( X[1] - x[1] ) / dy ) * smoothedDeltaFunction( ( X[2] - x[2] ) / dz );
+}
+
+} // namespace kernelweights
+
+
+/*! Interpolator for walberla::field::GhostLayerField with kernel strategy
+ *
+ * \ingroup field
+ *
+ * This interpolator uses a smoothed dirac kernel function to interpolate values.
+ * The applied weights are given in the namespace field::kernelweights.
+ * Needs the full neighborhood of the containing cell, i.e. 27 cells.
+ * Never construct this interpolator directly, but use the functionality from the FieldInterpolatorCreator.h instead.
+ */
+template< typename Field_T, typename FlagField_T >
+class KernelFieldInterpolator
+{
+public:
+
+   static const uint_t F_SIZE = Field_T::F_SIZE;
+
+   typedef Field_T                                      BaseField_T;
+   typedef typename FlagField_T::flag_t                 flag_t;
+   typedef KernelFieldInterpolator<Field_T,FlagField_T> OwnType;
+
+   KernelFieldInterpolator( const shared_ptr<StructuredBlockStorage> & blockStorage, const IBlock & block,
+                            const BaseField_T & baseField, const FlagField_T & flagField,
+                            const flag_t & evaluationMask )
+   : blockStorage_( blockStorage ), block_( block ), baseField_( baseField ), flagField_( flagField ), evaluationMask_( evaluationMask )
+   {
+      WALBERLA_ASSERT(baseField.nrOfGhostLayers() > uint_t(0), "field for kernel interpolation needs at least one ghost layer");
+   }
+
+
+   inline bool operator==( const OwnType & other ){ return baseField_ == other.baseField_; }
+
+   template< typename ForwardIterator_T >
+   inline void get( const Vector3<real_t> & position, ForwardIterator_T interpolationResultBegin )
+   {
+      get( position[0], position[1], position[2], interpolationResultBegin );
+   }
+
+   template< typename ForwardIterator_T >
+   inline void get( const real_t & x, const real_t & y, const real_t & z, ForwardIterator_T interpolationResultBegin )
+   {
+      WALBERLA_ASSERT(block_.getAABB().contains(x,y,z),
+                      "Interpolation position <" << x << ", " << y << ", " << z << "> is not contained inside the block of this interpolator with AABB " << block_.getAABB() << " !");
+
+      Cell centerCell = blockStorage_->getBlockLocalCell( block_, x, y, z );
+
+      const real_t dx = blockStorage_->dx( blockStorage_->getLevel( block_ ) );
+      const real_t dy = blockStorage_->dy( blockStorage_->getLevel( block_ ) );
+      const real_t dz = blockStorage_->dz( blockStorage_->getLevel( block_ ) );
+
+      const uint_t neighborhoodSize = uint_t(1);
+
+      CellInterval cellNeighborhood( centerCell[0] - cell_idx_c(neighborhoodSize), centerCell[1] - cell_idx_c(neighborhoodSize), centerCell[2] - cell_idx_c(neighborhoodSize),
+                                     centerCell[0] + cell_idx_c(neighborhoodSize), centerCell[1] + cell_idx_c(neighborhoodSize), centerCell[2] + cell_idx_c(neighborhoodSize) );
+
+      const uint_t kernelSizeOneDirection = uint_t(2) * neighborhoodSize + uint_t(1);
+      // store the calculated weighting factors of the available cells, i.e. cells flagged by the evaluation mask
+      std::vector<real_t> weights( kernelSizeOneDirection * kernelSizeOneDirection * kernelSizeOneDirection, real_t(0) );
+
+      // store the calculated weighting factors of the UNavailable cells, i.e. cells not included in the evaluation mask
+      std::vector<real_t> weightsUnavailable( kernelSizeOneDirection * kernelSizeOneDirection * kernelSizeOneDirection, real_t(0) );
+
+      cell_idx_t cellIdx0x = cellNeighborhood.xMin();
+      cell_idx_t cellIdx0y = cellNeighborhood.yMin();
+      cell_idx_t cellIdx0z = cellNeighborhood.zMin();
+      uint_t nx = kernelSizeOneDirection;
+      uint_t nxy = kernelSizeOneDirection * kernelSizeOneDirection;
+      Vector3<real_t> cellCenter0 = blockStorage_->getBlockLocalCellCenter( block_, Cell(cellIdx0x, cellIdx0y, cellIdx0z) ); // = cell in neighborhood with smallest x-, y-, and z-indices
+
+      // calculate kernel weights of all cells in neighborhood
+      for( uint_t k = uint_t(0); k < kernelSizeOneDirection; ++k)
+      {
+         for( uint_t j = uint_t(0); j < kernelSizeOneDirection; ++j)
+         {
+            for( uint_t i = uint_t(0); i < kernelSizeOneDirection; ++i)
+            {
+               Vector3<real_t> curCellCenter( cellCenter0[0] + real_c(i) * dx, cellCenter0[1] + real_c(j) * dy, cellCenter0[2] + real_c(k) * dz);
+               if( flagField_.isPartOfMaskSet( cellIdx0x + cell_idx_c(i), cellIdx0y + cell_idx_c(j), cellIdx0z + cell_idx_c(k), evaluationMask_ ) )
+               {
+                  weights[k*nxy+j*nx+i] = kernelweights::kernelWeightFunction( x, y, z, curCellCenter[0], curCellCenter[1], curCellCenter[2], dx, dy, dz );
+               } 
+               else
+               {
+                  weightsUnavailable[k*nxy+j*nx+i] = kernelweights::kernelWeightFunction( x, y, z, curCellCenter[0], curCellCenter[1], curCellCenter[2], dx, dy, dz );
+               }
+            }
+         }
+      }
+
+/*
+      // zero entries in weights array (and non-zero entries in weightsUnavailable) indicate non-fluid nodes
+      // weight correction to incorporate extrapolation for kernel interpolation, center element can not be redistributed
+      // without this part, the kernel interpolator can not extrapolate values
+      // this is based on experimental findings by the author and general correctness is not ensured, thus it is commented out
+      for( auto stenIt = stencil::D3Q27::beginNoCenter(); stenIt != stencil::D3Q27::end(); ++stenIt )
+      {
+         int cx = stenIt.cx();
+         int cy = stenIt.cy();
+         int cz = stenIt.cz();
+         int i = cx + 1;
+         int j = cy + 1;
+         int k = cz + 1;
+
+         if( weightsUnavailable[k*nxy+j*nx+i] > real_t(0) )
+         {
+            // check if we can distribute the non-fluid weight to nearby fluid weights that lie in one line inside the neighborhood
+            // it should generally not matter in which direction it is distributed
+            // check x direction
+            if( weights[k*nxy+j*nx+i-cx] > real_t(0) && weights[k*nxy+j*nx+i-2*cx] > real_t(0) )
+            {
+               weights[k*nxy+j*nx+i-cx] += real_t(2)*weightsUnavailable[k*nxy+j*nx+i];
+               weights[k*nxy+j*nx+i-2*cx] -= weightsUnavailable[k*nxy+j*nx+i];
+               weightsUnavailable[k*nxy+j*nx+i] = real_t(0);
+               continue;
+            }
+            // check y direction
+            if( weights[k*nxy+(j-cy)*nx+i] > real_t(0) && weights[k*nxy+(j-2*cy)*nx+i] > real_t(0) )
+            {
+               weights[k*nxy+(j-cy)*nx+i] += real_t(2)*weightsUnavailable[k*nxy+j*nx+i];
+               weights[k*nxy+(j-2*cy)*nx+i] -= weightsUnavailable[k*nxy+j*nx+i];
+               weightsUnavailable[k*nxy+j*nx+i] = real_t(0);
+               continue;
+            }
+            // check z direction
+            if( weights[(k-cz)*nxy+j*nx+i] > real_t(0) && weights[(k-2*cz)*nxy+j*nx+i] > real_t(0) )
+            {
+               weights[(k-cz)*nxy+j*nx+i] += real_t(2)*weightsUnavailable[k*nxy+j*nx+i];
+               weights[(k-2*cz)*nxy+j*nx+i] -= weightsUnavailable[k*nxy+j*nx+i];
+               weightsUnavailable[k*nxy+j*nx+i] = real_t(0);
+               continue;
+            }
+         }
+      }
+*/
+      // scale available weights by the total amount of unavailable weights such that afterwards sum over all weights is 1
+      const real_t sumOfWeightsUnavailable = std::accumulate(weightsUnavailable.begin(), weightsUnavailable.end(), real_t(0) );
+      const real_t sumOfWeights = std::accumulate(weights.begin(), weights.end(), real_t(0) );
+
+      // check if at least one cell was available, to prevent division by 0
+      if( sumOfWeights <= real_t(0) )
+         return;
+
+      const real_t scalingFactor = real_t(1) + sumOfWeightsUnavailable / sumOfWeights;
+
+      for( auto weightIt = weights.begin(); weightIt != weights.end(); ++weightIt )
+      {
+         *weightIt *= scalingFactor;
+      }
+
+      // interpolate value to interpolation position using the previously calculated weights
+      // values to not be included have a weight of 0
+      for( uint_t k = uint_t(0); k < kernelSizeOneDirection; ++k)
+      {
+         for( uint_t j = uint_t(0); j < kernelSizeOneDirection; ++j)
+         {
+            for( uint_t i = uint_t(0); i < kernelSizeOneDirection; ++i)
+            {
+               if ( weights[k*nxy+j*nx+i] > real_t(0) )
+               {
+                  Cell curCell( cellIdx0x + cell_idx_c(i), cellIdx0y + cell_idx_c(j), cellIdx0z + cell_idx_c(k) );
+                  addWeightedCellValue( interpolationResultBegin, curCell, weights[k*nxy+j*nx+i] );
+               }
+            }
+         }
+      }
+   }
+
+private:
+
+   template< typename ForwardIterator_T >
+   void addWeightedCellValue( ForwardIterator_T interpolationResultBegin, const Cell & curCell, const real_t & weighting )
+   {
+      for( uint_t f = uint_t(0); f < F_SIZE; ++f )
+      {
+         WALBERLA_ASSERT( !math::isnan(baseField_( curCell, f)), "NaN found in component " << f << " when interpolating from cell " << curCell );
+
+         *interpolationResultBegin += weighting * baseField_( curCell, f);
+         ++interpolationResultBegin;
+      }
+   }
+
+   shared_ptr<StructuredBlockStorage> blockStorage_;
+   const IBlock & block_;
+   const BaseField_T & baseField_;
+   const FlagField_T & flagField_;
+   flag_t evaluationMask_;
+
+};
+
+
+} // namespace field
+} // namespace walberla

src/field/interpolators/NearestNeighborFieldInterpolator.h

+//======================================================================================================================
+//
+//  This file is part of waLBerla. waLBerla is free software: you can
+//  redistribute it and/or modify it under the terms of the GNU General Public
+//  License as published by the Free Software Foundation, either version 3 of
+//  the License, or (at your option) any later version.
+//
+//  waLBerla is distributed in the hope that it will be useful, but WITHOUT
+//  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+//  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+//  for more details.
+//
+//  You should have received a copy of the GNU General Public License along
+//  with waLBerla (see COPYING.txt). If not, see <http://www.gnu.org/licenses/>.
+//
+//! \file NearestNeighborFieldInterpolator.h
+//! \ingroup field
+//! \author Christoph Rettinger <christoph.rettinger@fau.de>
+//
+//======================================================================================================================
+
+#pragma once
+
+#include "core/debug/Debug.h"
+
+#include "domain_decomposition/StructuredBlockStorage.h"
+
+#include "field/FlagField.h"
+
+namespace walberla {
+namespace field {
+
+/*! Interpolator for walberla::field::Field with nearest neighbor strategy
+ *
+ * \ingroup field
+ *
+ * This interpolator obtains the value from the nearest cell, flagged in the evaluation mask, of the interpolation position.
+ * This is usually the cell that contains the interpolation position.
+ * If this cell is a cell that is not within the evaluation mask, the direct neighborhood (8 cells) will be searched for an available cell.
+ * Never construct this interpolator directly, but use the functionality from FieldInterpolatorCreators.h instead.
+ */
+template< typename Field_T, typename FlagField_T >
+class NearestNeighborFieldInterpolator
+{
+public:
+
+   static const uint_t F_SIZE = Field_T::F_SIZE;
+
+   typedef Field_T                                               BaseField_T;
+   typedef typename FlagField_T::flag_t                          flag_t;
+   typedef NearestNeighborFieldInterpolator<Field_T,FlagField_T> OwnType;
+
+   NearestNeighborFieldInterpolator( const shared_ptr<StructuredBlockStorage> & blockStorage, const IBlock & block,
+                                     const BaseField_T & baseField, const FlagField_T & flagField,
+                                     const flag_t & evaluationMask )
+   : blockStorage_( blockStorage ), block_( block ), baseField_( baseField ), flagField_( flagField ), evaluationMask_( evaluationMask )
+   {}
+
+
+   inline bool operator==( const OwnType & other ){ return baseField_ == other.baseField_; }
+
+   template< typename ForwardIterator_T >
+   inline void get( const Vector3<real_t> & position, ForwardIterator_T interpolationResultBegin )
+   {
+      get( position[0], position[1], position[2], interpolationResultBegin );
+   }
+
+   template< typename ForwardIterator_T >
+   inline void get( const real_t & x, const real_t & y, const real_t & z, ForwardIterator_T interpolationResultBegin )
+   {
+
+      WALBERLA_ASSERT(block_.getAABB().contains(x,y,z),
+                      "Interpolation position <" << x << ", " << y << ", " << z << "> is not contained inside the block of this interpolator with AABB " << block_.getAABB() << " !");
+
+      Cell nearestCell = blockStorage_->getBlockLocalCell( block_, x, y, z );
+
+      if( flagField_.isPartOfMaskSet( nearestCell, evaluationMask_ ) )
+      {
+         for( uint_t f = uint_t(0); f < F_SIZE; ++f )
+         {
+            WALBERLA_ASSERT( !math::isnan( baseField_( nearestCell, f) ), "NaN found in component " << f << " when interpolating from cell " << nearestCell );
+            *interpolationResultBegin = baseField_( nearestCell, f);
+            ++interpolationResultBegin;
+         }
+      }
+      else
+      {
+         // look for available cell in direct neighborhood
+
+         CellInterval fieldXYZSize = baseField_.xyzSize();
+
+         Vector3<real_t> nearestCellCenter = blockStorage_->getBlockLocalCellCenter( block_, nearestCell );
+         const cell_idx_t xNeighbor = cell_idx_c( floor( x - nearestCellCenter[0] ) );
+         const cell_idx_t yNeighbor = cell_idx_c( floor( y - nearestCellCenter[1] ) );
+         const cell_idx_t zNeighbor = cell_idx_c( floor( z - nearestCellCenter[2] ) );
+
+         const cell_idx_t xMin = nearestCell.x() + xNeighbor;
+         const cell_idx_t yMin = nearestCell.y() + yNeighbor;
+         const cell_idx_t zMin = nearestCell.z() + zNeighbor;
+
+         for( cell_idx_t zC = zMin; zC <= zMin + cell_idx_t(1); ++zC)
+         {
+            for( cell_idx_t yC = yMin; yC <= yMin + cell_idx_t(1); ++yC)
+            {
+               for( cell_idx_t xC = xMin; xC <= xMin + cell_idx_t(1); ++xC)
+               {
+                  Cell curCell(xC,yC,zC);
+                  if( fieldXYZSize.contains(curCell) )
+                  {
+                     if (flagField_.isPartOfMaskSet(curCell, evaluationMask_))
+                     {
+                        for (uint_t f = uint_t(0); f < F_SIZE; ++f)
+                        {
+                           WALBERLA_ASSERT(!math::isnan(baseField_(curCell, f)),
+                                           "NaN found in component " << f << " when interpolating from cell "
+                                                                     << curCell);
+                           *interpolationResultBegin = baseField_(curCell, f);
+                           ++interpolationResultBegin;
+                        }
+                        break;
+                     }
+                  }
+               }
+            }
+         }
+      }
+   }
+
+private:
+
+   shared_ptr<StructuredBlockStorage> blockStorage_;
+   const IBlock & block_;
+   const BaseField_T & baseField_;
+   const FlagField_T & flagField_;
+   flag_t evaluationMask_;
+};
+
+} // namespace field
+} // namespace walberla

src/field/interpolators/TrilinearFieldInterpolator.h

+//======================================================================================================================
+//
+//  This file is part of waLBerla. waLBerla is free software: you can
+//  redistribute it and/or modify it under the terms of the GNU General Public
+//  License as published by the Free Software Foundation, either version 3 of
+//  the License, or (at your option) any later version.
+//
+//  waLBerla is distributed in the hope that it will be useful, but WITHOUT
+//  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+//  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+//  for more details.
+//
+//  You should have received a copy of the GNU General Public License along
+//  with waLBerla (see COPYING.txt). If not, see <http://www.gnu.org/licenses/>.
+//
+//! \file TrilinearFieldInterpolator.h
+//! \ingroup field
+//! \author Christoph Rettinger <christoph.rettinger@fau.de>
+//
+//======================================================================================================================
+
+#pragma once
+
+#include "core/debug/Debug.h"
+
+#include "domain_decomposition/StructuredBlockStorage.h"
+
+#include "field/FlagField.h"
+
+
+namespace walberla {
+namespace field {
+
+/*! Interpolator for walberla::field::GhostLayerField with trilinear strategy
+ *
+ * \ingroup field
+ *
+ * This interpolator uses trilinear interpolation to obtain the interpolated value from the interpolation position.
+ * If at least one of the cells, that are required for trilinear interpolation, i.e. the 8 closest cells,
+ * is not contained in the evaluation mask, the nearest-neighbor interpolation (see NearestNeighborFieldInterpolator.h)
+ * will be used instead.
+ * Never construct this interpolator directly, but use the functionality from FieldInterpolatorCreators.h instead.
+ */
+template< typename Field_T, typename FlagField_T >
+class TrilinearFieldInterpolator
+{
+public:
+
+   static const uint_t F_SIZE = Field_T::F_SIZE;
+
+   typedef Field_T                                         BaseField_T;
+   typedef typename FlagField_T::flag_t                    flag_t;
+   typedef TrilinearFieldInterpolator<Field_T,FlagField_T> OwnType;
+
+   TrilinearFieldInterpolator( const shared_ptr<StructuredBlockStorage> & blockStorage, const IBlock & block,
+                               const BaseField_T & baseField, const FlagField_T & flagField,
+                               const flag_t & evaluationMask )
+   : blockStorage_( blockStorage ), block_( block ), baseField_( baseField ), flagField_( flagField ), evaluationMask_( evaluationMask ),
+     nearestNeighborInterpolator_( blockStorage, block, baseField, flagField, evaluationMask )
+   {
+      WALBERLA_ASSERT(baseField.nrOfGhostLayers() > uint_t(0), "field for trilinear interpolation needs at least one ghost layer");
+   }
+
+
+   inline bool operator==( const OwnType & other ){ return baseField_ == other.baseField_; }
+
+   template< typename ForwardIterator_T >
+   inline void get( const Vector3<real_t> & position, ForwardIterator_T interpolationResultBegin )
+   {