libMesh::TriangleInterface Class Reference

#include <mesh_triangle_interface.h>

Classes
class	ArbitraryHole
class	Hole
	Class for parameterizing 2D holes to be meshed with Triangle. More...
class	PolygonHole

Public Types
enum	TriangulationType { GENERATE_CONVEX_HULL = 0, PSLG = 1, INVALID_TRIANGULATION_TYPE }

Public Member Functions
	TriangleInterface (UnstructuredMesh &mesh)
	~TriangleInterface ()
void	triangulate ()
ElemType &	elem_type ()
Real &	desired_area ()
Real &	minimum_angle ()
std::string &	extra_flags ()
TriangulationType &	triangulation_type ()
bool &	insert_extra_points ()
bool &	smooth_after_generating ()
void	attach_hole_list (const std::vector< Hole *> *holes)

Public Attributes
std::vector< std::pair< unsigned int, unsigned int > >	segments

Private Attributes
UnstructuredMesh &	_mesh
const std::vector< Hole * > *	_holes
ElemType	_elem_type
Real	_desired_area
Real	_minimum_angle
std::string	_extra_flags
TriangulationType	_triangulation_type
bool	_insert_extra_points
bool	_smooth_after_generating
MeshSerializer	_serializer

Detailed Description

A C++ interface between LibMesh and the Triangle library written by J.R. Shewchuk.

Author

John W. Peterson

Date

2011

Definition at line 57 of file mesh_triangle_interface.h.

Member Enumeration Documentation

TriangulationType

enum libMesh::TriangleInterface::TriangulationType

The TriangulationType is used with the general triangulate function defined below.

Enumerator
GENERATE_CONVEX_HULL	Uses the triangle library to first generate a convex hull from the set of points passed in, and then triangulate this set of points. This is probably the most common type of usage.
PSLG	Use the triangle library to triangulate a Planar Straight Line Graph which is defined implicitly by the order of the "points" vector: a straight line is assumed to lie between each successive pair of points, with an additional line joining the final and first points. In case your triangulation is a little too "structured" looking (which can happen when the initial PSLG is really simple) you can try to make the resulting triangulation a little more "unstructured" looking by setting insert_points to true in the triangulate() function.
INVALID_TRIANGULATION_TYPE	Does nothing, used as a default value.

Definition at line 78 of file mesh_triangle_interface.h.

    {
      GENERATE_CONVEX_HULL = 0,

      PSLG = 1,

      INVALID_TRIANGULATION_TYPE
    };

Constructor & Destructor Documentation

TriangleInterface()

libMesh::TriangleInterface::TriangleInterface ( UnstructuredMesh &  mesh )

explicit

The constructor. A reference to the mesh containing the points which are to be triangulated must be provided. Unless otherwise specified, a convex hull will be computed for the set of input points and the convex hull will be meshed.

Definition at line 44 of file mesh_triangle_interface.C.

  : _mesh(mesh),
    _holes(nullptr),
    _elem_type(TRI3),
    _desired_area(0.1),
    _minimum_angle(20.0),
    _extra_flags(""),
    _triangulation_type(GENERATE_CONVEX_HULL),
    _insert_extra_points(false),
    _smooth_after_generating(true),
    _serializer(_mesh)
{}

~TriangleInterface()

libMesh::TriangleInterface::~TriangleInterface ( )

inline

Empty destructor.

Definition at line 72 of file mesh_triangle_interface.h.

{}

Member Function Documentation

attach_hole_list()

void libMesh::TriangleInterface::attach_hole_list ( const std::vector< Hole *> *  holes )

inline

Attaches a vector of Hole* pointers which will be meshed around.

Definition at line 162 of file mesh_triangle_interface.h.

References _holes.

Referenced by libMesh::MeshTools::Generation::build_delaunay_square().

{_holes = holes;}

desired_area()

Real& libMesh::TriangleInterface::desired_area ( )

inline

Sets and/or gets the desired triangle area. Set to zero to disable area constraint.

Definition at line 129 of file mesh_triangle_interface.h.

References _desired_area.

Referenced by libMesh::MeshTools::Generation::build_delaunay_square().

{return _desired_area;}

elem_type()

ElemType& libMesh::TriangleInterface::elem_type ( )

inline

Sets and/or gets the desired element type.

Definition at line 123 of file mesh_triangle_interface.h.

References _elem_type.

Referenced by libMesh::MeshTools::Generation::build_delaunay_square().

{return _elem_type;}

extra_flags()

std::string& libMesh::TriangleInterface::extra_flags ( )

inline

Sets and/or gets additional flags to be passed to triangle

Definition at line 140 of file mesh_triangle_interface.h.

References _extra_flags.

{return _extra_flags;}

insert_extra_points()

bool& libMesh::TriangleInterface::insert_extra_points ( )

inline

Sets and/or gets the flag for inserting add'l points.

Definition at line 150 of file mesh_triangle_interface.h.

References _insert_extra_points.

{return _insert_extra_points;}

minimum_angle()

Real& libMesh::TriangleInterface::minimum_angle ( )

inline

Sets and/or gets the minimum angle. Set to zero to disable area constraint.

Definition at line 135 of file mesh_triangle_interface.h.

References _minimum_angle.

{return _minimum_angle;}

smooth_after_generating()

bool& libMesh::TriangleInterface::smooth_after_generating ( )

inline

Sets/gets flag which tells whether to do Delaunay mesh smoothing after generating the grid.

Definition at line 156 of file mesh_triangle_interface.h.

References _smooth_after_generating.

{return _smooth_after_generating;}

triangulate()

void libMesh::TriangleInterface::triangulate

(

)

This is the main public interface for this function. Internally, it calls Triangle's triangulate routine.

Definition at line 60 of file mesh_triangle_interface.C.

References _desired_area, _elem_type, _extra_flags, _holes, _insert_extra_points, _mesh, _minimum_angle, _smooth_after_generating, _triangulation_type, libMesh::MeshBase::add_point(), libMesh::MeshBase::clear(), libMesh::TriangleWrapper::copy_tri_to_mesh(), libMesh::TriangleWrapper::destroy(), GENERATE_CONVEX_HULL, libMesh::TriangleWrapper::init(), libMesh::TriangleWrapper::INPUT, INVALID_TRIANGULATION_TYPE, libMesh::MeshBase::n_nodes(), libMesh::MeshBase::node_ptr_range(), libMesh::TriangleWrapper::OUTPUT, libMesh::MeshBase::prepare_for_use(), PSLG, segments, libMesh::MeshBase::set_mesh_dimension(), libMesh::LaplaceMeshSmoother::smooth(), libMesh::TOLERANCE, libMesh::TRI3, and libMesh::TRI6.

Referenced by libMesh::MeshTools::Generation::build_delaunay_square().

{
  // Will the triangulation have holes?
  const bool have_holes = ((_holes != nullptr) && (!_holes->empty()));

  // If the initial PSLG is really simple, e.g. an L-shaped domain or
  // a square/rectangle, the resulting triangulation may be very
  // "structured" looking.  Sometimes this is a problem if your
  // intention is to work with an "unstructured" looking grid.  We can
  // attempt to work around this limitation by inserting midpoints
  // into the original PSLG.  Inserting additional points into a
  // set of points meant to be a convex hull usually makes less sense.

  // May or may not need to insert new points ...
  if ((_triangulation_type==PSLG) && (_insert_extra_points))
    {
      // Make a copy of the original points from the Mesh
      std::vector<Point> original_points;
      original_points.reserve (_mesh.n_nodes());
      for (auto & node : _mesh.node_ptr_range())
        original_points.push_back(*node);

      // Clear out the mesh
      _mesh.clear();

      // Make sure the new Mesh will be 2D
      _mesh.set_mesh_dimension(2);

      // Insert a new point on each PSLG at some random location
      // np=index into new points vector
      // n =index into original points vector
      for (std::size_t np=0, n=0; np<2*original_points.size(); ++np)
        {
          // the even entries are the original points
          if (np%2==0)
            _mesh.add_point(original_points[n++]);

          else // the odd entries are the midpoints of the original PSLG segments
            _mesh.add_point ((original_points[n] + original_points[n-1])/2);
        }
    }

  // Regardless of whether we added additional points, the set of points to
  // triangulate is now sitting in the mesh.

  // If the holes vector is non-nullptr (and non-empty) we need to determine
  // the number of additional points which the holes will add to the
  // triangulation.
  unsigned int n_hole_points = 0;

  if (have_holes)
    {
      for (std::size_t i=0; i<_holes->size(); ++i)
        n_hole_points += (*_holes)[i]->n_points();
    }

  // Triangle data structure for the mesh
  TriangleWrapper::triangulateio initial;
  TriangleWrapper::triangulateio final;

  // Pseudo-Constructor for the triangle io structs
  TriangleWrapper::init(initial);
  TriangleWrapper::init(final);

  initial.numberofpoints = _mesh.n_nodes() + n_hole_points;
  initial.pointlist      = static_cast<REAL*>(std::malloc(initial.numberofpoints * 2 * sizeof(REAL)));

  if (_triangulation_type==PSLG)
    {
      // Implicit segment ordering: One segment per point, including hole points
      if (this->segments.empty())
        initial.numberofsegments = initial.numberofpoints;

      // User-defined segment ordering: One segment per entry in the segments vector
      else
        initial.numberofsegments = this->segments.size();
    }

  else if (_triangulation_type==GENERATE_CONVEX_HULL)
    initial.numberofsegments = n_hole_points; // One segment for each hole point

  // Debugging
  // libMesh::out << "Number of segments set to: " << initial.numberofsegments << std::endl;

  // Allocate space for the segments (2 int per segment)
  if (initial.numberofsegments > 0)
    {
      initial.segmentlist = static_cast<int *> (std::malloc(initial.numberofsegments * 2 * sizeof(int)));
    }


  // Copy all the holes' points and segments into the triangle struct.

  // The hole_offset is a constant offset into the points vector which points
  // past the end of the last hole point added.
  unsigned int hole_offset=0;

  if (have_holes)
    for (std::size_t i=0; i<_holes->size(); ++i)
      {
        for (unsigned int ctr=0, h=0; h<(*_holes)[i]->n_points(); ctr+=2, ++h)
          {
            Point p = (*_holes)[i]->point(h);

            const unsigned int index0 = 2*hole_offset+ctr;
            const unsigned int index1 = 2*hole_offset+ctr+1;

            // Save the x,y locations in the triangle struct.
            initial.pointlist[index0] = p(0);
            initial.pointlist[index1] = p(1);

            // Set the points which define the segments
            initial.segmentlist[index0] = hole_offset+h;
            initial.segmentlist[index1] = (h==(*_holes)[i]->n_points()-1) ? hole_offset : hole_offset+h+1; // wrap around
          }

        // Update the hole_offset for the next hole
        hole_offset += (*_holes)[i]->n_points();
      }


  // Copy all the non-hole points and segments into the triangle struct.
  {
    dof_id_type ctr=0;
    for (auto & node : _mesh.node_ptr_range())
      {
        dof_id_type index = 2*hole_offset + ctr;

        // Set x,y values in pointlist
        initial.pointlist[index] = (*node)(0);
        initial.pointlist[index+1] = (*node)(1);

        // If the user requested a PSLG, the non-hole points are also segments
        if (_triangulation_type==PSLG)
          {
            // Use implicit ordering to define segments
            if (this->segments.empty())
              {
                dof_id_type n = ctr/2; // ctr is always even
                initial.segmentlist[index] = hole_offset+n;
                initial.segmentlist[index+1] = (n==_mesh.n_nodes()-1) ? hole_offset : hole_offset+n+1; // wrap around
              }
          }

        ctr +=2;
      }
  }


  // If the user provided it, use his ordering to define the segments
  for (std::size_t ctr=0, s=0; s<this->segments.size(); ctr+=2, ++s)
    {
      const unsigned int index0 = 2*hole_offset+ctr;
      const unsigned int index1 = 2*hole_offset+ctr+1;

      initial.segmentlist[index0] = hole_offset + this->segments[s].first;
      initial.segmentlist[index1] = hole_offset + this->segments[s].second;
    }



  // Tell the input struct about the holes
  if (have_holes)
    {
      initial.numberofholes = _holes->size();
      initial.holelist      = static_cast<REAL*>(std::malloc(initial.numberofholes * 2 * sizeof(REAL)));
      for (std::size_t i=0, ctr=0; i<_holes->size(); ++i, ctr+=2)
        {
          Point inside_point = (*_holes)[i]->inside();
          initial.holelist[ctr]   = inside_point(0);
          initial.holelist[ctr+1] = inside_point(1);
        }
    }

  // Set the triangulation flags.
  // c ~ enclose convex hull with segments
  // z ~ use zero indexing
  // B ~ Suppresses boundary markers in the output
  // Q ~ run in "quiet" mode
  // p ~ Triangulates a Planar Straight Line Graph
  //     If the `p' switch is used, `segmentlist' must point to a list of
  //     segments, `numberofsegments' must be properly set, and
  //     `segmentmarkerlist' must either be set to nullptr (in which case all
  //     markers default to zero), or must point to a list of markers.
  // D ~ Conforming Delaunay: use this switch if you want all triangles
  //     in the mesh to be Delaunay, and not just constrained Delaunay
  // q ~  Quality mesh generation with no angles smaller than 20 degrees.
  //      An alternate minimum angle may be specified after the q
  // a ~ Imposes a maximum triangle area constraint.
  // -P  Suppresses the output .poly file. Saves disk space, but you lose the ability to maintain
  //     constraining segments on later refinements of the mesh.
  // Create the flag strings, depends on element type
  std::ostringstream flags;

  // Default flags always used
  flags << "zBPQ";

  // Flags which are specific to the type of triangulation
  switch (_triangulation_type)
    {
    case GENERATE_CONVEX_HULL:
      {
        flags << "c";
        break;
      }

    case PSLG:
      {
        flags << "p";
        break;
      }

    case INVALID_TRIANGULATION_TYPE:
      libmesh_error_msg("ERROR: INVALID_TRIANGULATION_TYPE selected!");

    default:
      libmesh_error_msg("Unrecognized _triangulation_type");
    }


  // Flags specific to the type of element
  switch (_elem_type)
    {
    case TRI3:
      {
        // do nothing.
        break;
      }

    case TRI6:
      {
        flags << "o2";
        break;
      }

    default:
      libmesh_error_msg("ERROR: Unrecognized triangular element type.");
    }


  // If we do have holes and the user asked to GENERATE_CONVEX_HULL,
  // need to add the p flag so the triangulation respects those segments.
  if ((_triangulation_type==GENERATE_CONVEX_HULL) && (have_holes))
    flags << "p";

  // Finally, add the area constraint
  if (_desired_area > TOLERANCE)
    flags << "a" << std::fixed << _desired_area;

  // add minimum angle constraint
  if (_minimum_angle > TOLERANCE)
    flags << "q" << std::fixed << _minimum_angle;

  // add user provided extra flags
  if (_extra_flags.size() > 0)
    flags << _extra_flags;

  // Refine the initial output to conform to the area constraint
  TriangleWrapper::triangulate(const_cast<char *>(flags.str().c_str()),
                               &initial,
                               &final,
                               nullptr); // voronoi ouput -- not used


  // Send the information computed by Triangle to the Mesh.
  TriangleWrapper::copy_tri_to_mesh(final,
                                    _mesh,
                                    _elem_type);

  // To the naked eye, a few smoothing iterations usually looks better,
  // so we do this by default unless the user says not to.
  if (this->_smooth_after_generating)
    LaplaceMeshSmoother(_mesh).smooth(2);


  // Clean up.
  TriangleWrapper::destroy(initial,      TriangleWrapper::INPUT);
  TriangleWrapper::destroy(final,        TriangleWrapper::OUTPUT);

  // Prepare the mesh for use before returning.  This ensures (among
  // other things) that it is partitioned and therefore users can
  // iterate over local elements, etc.
  _mesh.prepare_for_use();
}

triangulation_type()

TriangulationType& libMesh::TriangleInterface::triangulation_type ( )

inline

Sets and/or gets the desired triangulation type.

Definition at line 145 of file mesh_triangle_interface.h.

References _triangulation_type.

Referenced by libMesh::MeshTools::Generation::build_delaunay_square().

{return _triangulation_type;}

Member Data Documentation

_desired_area

Real libMesh::TriangleInterface::_desired_area

private

The desired area for the elements in the resulting mesh.

Definition at line 198 of file mesh_triangle_interface.h.

Referenced by desired_area(), and triangulate().

_elem_type

ElemType libMesh::TriangleInterface::_elem_type

private

The type of elements to generate. (Defaults to TRI3).

Definition at line 193 of file mesh_triangle_interface.h.

Referenced by elem_type(), and triangulate().

_extra_flags

std::string libMesh::TriangleInterface::_extra_flags

private

Additional flags to be passed to triangle

Definition at line 208 of file mesh_triangle_interface.h.

Referenced by extra_flags(), and triangulate().

_holes

const std::vector<Hole*>* libMesh::TriangleInterface::_holes

private

A pointer to a vector of Hole*s. If this is nullptr, there are no holes!

Definition at line 187 of file mesh_triangle_interface.h.

Referenced by attach_hole_list(), and triangulate().

_insert_extra_points

bool libMesh::TriangleInterface::_insert_extra_points

private

Flag which tells whether or not to insert additional nodes before triangulation. This can sometimes be used to "de-regularize" the resulting triangulation.

Definition at line 222 of file mesh_triangle_interface.h.

Referenced by insert_extra_points(), and triangulate().

_mesh

UnstructuredMesh& libMesh::TriangleInterface::_mesh

private

Reference to the mesh which is to be created by triangle.

Definition at line 181 of file mesh_triangle_interface.h.

Referenced by triangulate().

_minimum_angle

Real libMesh::TriangleInterface::_minimum_angle

private

Minimum angle in triangles

Definition at line 203 of file mesh_triangle_interface.h.

Referenced by minimum_angle(), and triangulate().

_serializer

MeshSerializer libMesh::TriangleInterface::_serializer

private

Triangle only operates on serial meshes.

Definition at line 233 of file mesh_triangle_interface.h.

_smooth_after_generating

bool libMesh::TriangleInterface::_smooth_after_generating

private

Flag which tells whether we should smooth the mesh after it is generated. True by default.

Definition at line 228 of file mesh_triangle_interface.h.

Referenced by smooth_after_generating(), and triangulate().

_triangulation_type

TriangulationType libMesh::TriangleInterface::_triangulation_type

private

The type of triangulation to perform: choices are: convex hull PSLG

Definition at line 215 of file mesh_triangle_interface.h.

Referenced by triangulate(), and triangulation_type().

segments

std::vector<std::pair<unsigned int, unsigned int> > libMesh::TriangleInterface::segments

When constructing a PSLG, it is often not possible to do so implicitly through the ordering of the points. You can use the segments vector to specify the segments explicitly, Ex: unit square numbered counter-clockwise starting from origin segments[0] = (0,1) segments[1] = (1,2) segments[2] = (2,3) segments[3] = (3,0) For this case you could actually use the implicit ordering!

Definition at line 175 of file mesh_triangle_interface.h.

Referenced by triangulate().

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The documentation for this class was generated from the following files:

• mesh_triangle_interface.h
• mesh_triangle_interface.C