CGAL users discussion list

[许春旭 <>]

Hi all, 

I'm using the "2D Boolean Operations on Nef Polygon"package. I;m wondering how the structure of the Nef Polygon is organized: I read the part of the manual about the Explorer but still not very clear, so I run a test program. Following is the piece of code creating a rectangle area (0.0, 4.5) x (0.0, 1.0)

Nef_polyhedron N1(Line(1, 0, 0), Nef_polyhedron::EXCLUDED);

Nef_polyhedron N2(Line(0, 1, 0), Nef_polyhedron::EXCLUDED);

Nef_polyhedron N3(Line(-1, 0, 4.5), Nef_polyhedron::EXCLUDED);

Nef_polyhedron N4(Line(0, -1, 1), Nef_polyhedron::EXCLUDED);

and following is the code that traverses the area:

Explorer tE = N5.explorer();

auto faceIter = tE.faces_begin();  ++faceIter;

for (; faceIter != tE.faces_end(); ++faceIter)

{

cout << "New Face: " << endl;

Explorer::Halfedge_around_vertex_const_circulator heIter(tE.halfedge(faceIter));

auto heStartIter = heIter;

CGAL_For_all(heIter, heStartIter)

{

if (tE.is_standard(tE.target(heIter)) || tE.is_standard(tE.source(heIter)))

{

auto p = tE.source(heIter)->point();

cout << CGAL::to_double(p.x()) << " " << CGAL::to_double(p.y()) << " --> ";

p = tE.target(heIter)->point();

cout << CGAL::to_double(p.x()) << " " << CGAL::to_double(p.y()) << endl;

}

}

}

I though at least one face should show all four edges of the rectangle, like this:

New Face: 

0 1 --> 0 0

0 0 --> 4.5 0

4.5 0 --> 4.5 1

4.5 1 --> 0 1

, but the output is like this:

New Face:

New Face:

0 1 --> 0 0

0 1 --> 4.5 1

Where am I understanding it wrong? Thanks very much.

Best regards.

Chunxu Xu

Department of Computer Science and Technology

Tsinghua University

Beijing

People's Republic of China