CGAL users discussion list

[Tony Apicella <>]

I simulated a gray scale volume of 32x32x32 voxels with a solid sphere of radius 8.

make_surface_mesh produces a mesh only over a portion of the sphere.

If I simulate a sphere with a smaller radius, then make_surface_mesh produces a mesh around the entire sphere.

If I simulate a sphere of radius 12, then make_surface_mesh takes a very long time, I did not wait for it to complete.

Here is the code I used.  One INR volume of the sphere having radius 8 is attached.

Thank you.

#include <iostream>

main()

{

string path("-----somewhere------------");

name = "sphere4";

string file = path + name;

file += ".INR";

Tr tr;            // 3D-Delaunay triangulation

C2t3 c2t3(tr);   // 2D-complex in 3D-Delaunay triangulation

// the 'function' is a 3D gray level image

std::cout << "Reading INR: " << file << std::endl;

float thresh = 2.9f;

Gray_level_image image( file.c_str(), thresh );

std::cout << "Completed reading INR with threshold" << thresh << std::endl;

// Carefully chosen bounding sphere: the center must be inside the

// surface defined by 'image' and the radius must be high enough so that

// the sphere actually bounds the whole image.

float xspan = float(image.xdim() * image.vx());

float yspan = float(image.ydim() * image.vy());

float zspan = float(image.zdim() * image.vz());

GT::Point_3 bounding_sphere_center(xspan / 2, yspan / 2, zspan / 2);

float span = sqrt(xspan * xspan + yspan * yspan + zspan * zspan);

GT::FT bounding_sphere_squared_radius = span;

GT::Sphere_3 bounding_sphere(bounding_sphere_center, bounding_sphere_squared_radius);

// definition of the surface, with relative precision

std::cout << "Define surface" << std::endl;

Surface_3 surface(image, bounding_sphere, 1e-2);

// defining meshing criteria

std::cout << "Defining mesh criteria" << std::endl;

// defining meshing criteria

CGAL::Surface_mesh_default_criteria_3<Tr> criteria(30.0f, 0.5f, 1.414f);

// meshing surface, with the "manifold without boundary" algorithm

std::cout << "Making mesh" << std::endl;

CGAL::make_surface_mesh(c2t3, surface, criteria, CGAL::Non_manifold_tag());

file = path + name;

file += ".off";

std::cout << "Writing to " << file << endl;

std::ofstream out(file);

CGAL::output_surface_facets_to_off(out, c2t3);

std::cout << "Final number of points: " << tr.number_of_vertices() << "\n";

}

Attachment: sphere8.INR
Description: sphere8.INR