Reference Manual

Qijia Huang

The package provides an implementation of a dynamic approximation of the medial axis inspired by variational shape approximation

Introduced in: CGAL 6.2
Depends on: 2D and 3D Fast Intersection and Distance Computation
BibTeX: cgal:dsvvmas-h-25b
License: GPL

Classified Reference Pages

Functions

• CGAL::extract_variational_medial_skeleton()

Classes

• CGAL::Variational_medial_axis
• CGAL::Medial_Skeleton

Modules
	Traits Classes

Classes
class	CGAL::Medial_Skeleton< TriangleMesh_, GeomTraits_ >
	Class representing the medial skeleton of a shape. More...
class	CGAL::Variational_medial_axis< TriangleMesh_, ConcurrencyTag_, AccelerationType_, GeomTraits_, VertexPointMap_ >
	Algorithm class for extracting a variational medial skeleton from a triangulated surface mesh. More...
class	CGAL::Fast_winding_number< TriangleMesh, FaceNormalMap, FaceAreaMap, FaceCentroidMap, Tree, ORDER, GeomTraits, VertexPointMap >
	Fast evaluation of the (normalized) winding number of a triangle mesh. More...

Functions
template<class TriangleMesh , class NamedParameters = parameters::Default_named_parameters>
CGAL::Medial_Skeleton< TriangleMesh >	CGAL::extract_variational_medial_skeleton (const TriangleMesh &tmesh, const NamedParameters &np=parameters::default_values())
	extracts a medial skeleton for the triangle mesh tmesh.
template<typename TriangleMesh , typename GeomTraits , class NamedParameters = parameters::Default_named_parameters>
bool	CGAL::IO::write_PLY (const Medial_Skeleton< TriangleMesh, GeomTraits > &skeleton, const std::string &filepath, const NamedParameters &np=parameters::default_values())
	writes the medial skeleton to a PLY file.

Function Documentation

extract_variational_medial_skeleton()

template<class TriangleMesh , class NamedParameters = parameters::Default_named_parameters>

CGAL::Medial_Skeleton< TriangleMesh > CGAL::extract_variational_medial_skeleton	(	const TriangleMesh &	tmesh,
		const NamedParameters &	np = parameters::default_values()
	)

#include <CGAL/extract_variational_medial_skeleton.h>

extracts a medial skeleton for the triangle mesh tmesh.

This function uses the class CGAL::Variational_medial_axis_sampling with the default parameters.

Precondition

tmesh is a triangle mesh without borders

The specialization boost::property_map<TriangleMesh, CGAL::vertex_point_t>::const_type and get(vertex_point, tmesh) are defined.

The value type of boost::property_map<TriangleMesh, CGAL::vertex_point_t>::const_type is a point type from a CGAL Kernel.

Template Parameters

TriangleMesh	a model of FaceListGraph
NamedParameters	a sequence of Named Parameters

Parameters

tmesh	input mesh
np	an optional sequence of Named Parameters, listed below:

Optional Named Parameters

number_of_spheres The desired number of medial spheres in the resulting skeleton. Type: unsigned int Default: 100 Extra: This number should generally not exceed 300, as the method is designed to produce coarse skeletons.
number_of_samples The number of samples on the surface mesh to use for the optimization process. Type: unsigned int Default: max(20000, number_of_spheres * 100) Extra: The number of samples should be significantly larger than the number of spheres.(x100 at least)
max_iteration_number The maximum number of iterations for the optimization process. Type: int Default: 1000 Extra: This parameter must be strictly positive; setting it to zero may prevent correct skeleton connectivity construction.
lambda A weight balancing the two energy terms (SQEM and Euclidean). Smaller values tend to produce skeletons that follow local features more closely. Type: FT Default: FT(0.2) Extra: The range of this parameter is (0,1].
random_seed The random seed to sample points on the triangle mesh surface. Type: unsigned int Extra: Fix the random seed so that the result can be reproduced
concurrency_tag Tag indicating whether the algorithm should run sequentially or in parallel. Type: Concurrency tag type Default: CGAL::Sequential_tag Extra: Use CGAL::Parallel_tag for parallel execution (requires TBB).
acceleration_structure Tag indicating the type of acceleration structure to use. Type: Acceleration structure tag type Default: CGAL::KD_tree_tag Extra: Use CGAL::BVH_tag for a bounding volume hierarchy.

write_PLY()

template<typename TriangleMesh , typename GeomTraits , class NamedParameters = parameters::Default_named_parameters>

bool CGAL::IO::write_PLY	(	const Medial_Skeleton< TriangleMesh, GeomTraits > &	skeleton,
		const std::string &	filepath,
		const NamedParameters &	np = parameters::default_values()
	)

#include <CGAL/variational_medial_axis_sampling.h>

writes the medial skeleton to a PLY file.

Template Parameters

TriangleMesh	a model of FaceListGraph
GeomTraits	a model of Kernel
NamedParameters	a sequence of Named Parameters

Parameters

skeleton	The medial skeleton to write.
filepath	The name of the file to write to.
np	optional Named Parameters described below

Optional Named Parameters

stream_precision a parameter used to set the precision (i.e. how many digits are generated) of the output stream Type: int Default: the precision of the stream os

Note: This function writes the medial skeleton to a PLY file in ASCII format. The format is :

ply
format ascii 1.0
element vertex N
property float x
property float y
property float z
property float radius
element edge M
property int vertex1
property int vertex2
element face K
property list uchar int vertex_indices
end_header
x1 y1 z1 r1
...        //N vertices
xN yN zN rN
v1 v2
...        //M edges
vM vN
3 v1 v2 v3
...        //K faces
3 vX vY vZ

Returns

true if writing was successful, false otherwise.