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[Tony Apicella <>]

Thank you Sebastien.

I did update the radius each time.  But it was updated incorrectly.  The argument to the Sphere_3 class constructor is the square of the radius, but I used only the radius.

---

From: <> on behalf of Sebastien Loriot <>
Sent: Monday, January 4, 2021 9:19 AM
To: <>
Subject: Re: [cgal-discuss] Help with make_surface_mesh

 

Did you update the radius of the bounding sphere each time?


Sebastien.


On 1/4/21 5:42 PM, Tony Apicella wrote:
>
>
> 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";
>
> }
>
>
>
>
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