point_locator_nanoflann.h

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// The libMesh Finite Element Library.
// Copyright (C) 2002-2025 Benjamin S. Kirk, John W. Peterson, Roy H. Stogner

// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.

// This library 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
// Lesser General Public License for more details.

// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA



#ifndef LIBMESH_POINT_LOCATOR_NANOFLANN_H
#define LIBMESH_POINT_LOCATOR_NANOFLANN_H

#include "libmesh/libmesh_config.h"

// This class is not defined unless libmesh is built with Nanoflann support
#ifdef LIBMESH_HAVE_NANOFLANN

// libmesh includes
#include "libmesh/point_locator_base.h"
#include "libmesh/point.h"
#include "libmesh/bounding_box.h"

// contrib includes
#include "libmesh/nanoflann.hpp"

// C++ includes
#include <vector>
#include <memory>

namespace libMesh
{

// Forward Declarations
class MeshBase;
class Point;
class Elem;

class PointLocatorNanoflann : public PointLocatorBase
{
public:
  PointLocatorNanoflann (const MeshBase & mesh,
                         const PointLocatorBase * master = nullptr);

  virtual ~PointLocatorNanoflann ();

  virtual void clear() override final;

  virtual void init() override final;

  virtual const Elem * operator() (const Point & p,
                                   const std::set<subdomain_id_type> * allowed_subdomains = nullptr) const override final;

  virtual void operator() (const Point & p,
                           std::set<const Elem *> & candidate_elements,
                           const std::set<subdomain_id_type> * allowed_subdomains = nullptr) const override final;

  virtual void enable_out_of_mesh_mode () override final;

  virtual void disable_out_of_mesh_mode () override final;

  std::size_t get_num_results() const;
  void set_num_results(std::size_t val);

  //
  // Required Nanoflann typedefs and APIs
  //

  typedef Real coord_t;

  std::size_t kdtree_get_point_count() const;

  coord_t kdtree_distance(const coord_t * p1,
                          const std::size_t idx_p2,
                          std::size_t size) const;

  coord_t kdtree_get_pt(const std::size_t idx, int dim) const;

  template <class BBOX>
  bool kdtree_get_bbox(BBOX & /*bb*/) const { return false; }

protected:

  bool _out_of_mesh_mode;

  std::size_t _num_results;

  std::shared_ptr<std::vector<const Elem *>> _elems;
  std::shared_ptr<std::vector<Point>> _point_cloud;

  // kd_tree will be initialized during init() and then automatically
  // cleaned up by the destructor. We always create a LIBMESH_DIM
  // dimensional Nanoflann object.
  typedef nanoflann::L2_Simple_Adaptor<Real, PointLocatorNanoflann> adapter_t;
  typedef nanoflann::KDTreeSingleIndexAdaptor<adapter_t, PointLocatorNanoflann, LIBMESH_DIM> kd_tree_t;
  std::shared_ptr<kd_tree_t> _kd_tree;

  mutable std::vector<std::size_t> _ret_index;
  mutable std::vector<Real> _out_dist_sqr;

  mutable std::vector<std::size_t> _b;

  nanoflann::KNNResultSet<Real>
  kd_tree_find_neighbors(const Point & p,
                         std::size_t num_results) const;
};

} // namespace libMesh

#endif // LIBMESH_HAVE_NANOFLANN
#endif // LIBMESH_POINT_LOCATOR_NANOFLANN_H