DGtal  1.2.beta
geometry/tools/exampleRationalBallQuickHull3D.cpp

Computation of the convex hull of a set of real points in 3D by Quick Hull algorithm.

# 1000000 points in digital ball of radius 1000 with precision 1024
./examples/geometry/tools/exampleRationalBallQuickHull3D 1000000 1000 1024

outputs

#points=1000000 #vertices=4490 #facets=8975
purge duplicates= 254 ms.
init simplex    = 29 ms.
quickhull core  = 326 ms.
compute vertices= 24 ms.
total time      = 634 ms.
See also
QuickHull algorithm in arbitrary dimension for convex hull and Delaunay cell complex computation
#include "DGtal/base/Common.h"
#include "DGtal/geometry/tools/QuickHull.h"
#include "DGtal/shapes/SurfaceMesh.h"
#include "DGtal/io/writers/SurfaceMeshWriter.h"
double rand01() { return (double) rand() / (double) RAND_MAX; }
using namespace DGtal::Z3i;
int main( int argc, char* argv[] )
{
int nb = argc > 1 ? atoi( argv[ 1 ] ) : 100; // nb points
double R = argc > 2 ? atof( argv[ 2 ] ) : 10.0; // radius of ball
double precision = argc > 3 ? atof( argv[ 3 ] ) : 1024.0; // precision
// (0) typedefs
typedef DGtal::QuickHull< Kernel3D > QuickHull3D;
// (1) create range of random points in ball
std::vector< RealPoint > V;
const double R2 = R * R;
for ( int i = 0; i < nb; ) {
RealPoint p( rand01()*2.0*R - R, rand01()*2.0*R - R, rand01()*2.0*R - R );
if ( p.squaredNorm() < R2 ) { V.push_back( p ); i++; }
}
// (2) compute convex hull
Kernel3D kernel( precision );
QuickHull3D hull( kernel );
hull.setInput( V );
hull.computeConvexHull();
std::cout << "#points=" << hull.nbPoints()
<< " #vertices=" << hull.nbVertices()
<< " #facets=" << hull.nbFacets() << std::endl;
double total_time = 0;
std::for_each( hull.timings.cbegin(), hull.timings.cend(),
[&total_time] ( double t ) { total_time += t; } );
std::cout << "purge duplicates= " << round(hull.timings[ 0 ]) << " ms." << std::endl;
std::cout << "init simplex = " << round(hull.timings[ 1 ]) << " ms." << std::endl;
std::cout << "quickhull core = " << round(hull.timings[ 2 ]) << " ms." << std::endl;
std::cout << "compute vertices= " << round(hull.timings[ 3 ]) << " ms." << std::endl;
std::cout << "total time = " << round(total_time) << " ms." << std::endl;
// (3) build mesh
std::vector< RealPoint > positions;
hull.getVertexPositions( positions );
std::vector< std::vector< std::size_t > > facets;
hull.getFacetVertices( facets );
SMesh mesh( positions.cbegin(), positions.cend(), facets.cbegin(), facets.cend() );
// (4) output result as OBJ file
std::ofstream out( "qhull.obj" );
out.close();
return 0;
}