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[Samer Afach <>]

Thank you for your reply.

Actually I'm concerned now before this with the question whether the
envelope algorithm offers the envelope as a function and not surfaces,
because I couldn't find a single function in the corresponding class
that does that. Does it do that? I mean I would like to give it a
polyhedron, and on the other side using minimum and maximum get the
envelopes as functions of x and y, is that possible?

I'd appreciate any efforts so much,
Thank you,
Samer



 wrote:
> You need to use an exact-predicate and exact-construction kernel. If
> you do that and the problem still occurs, please send the entire
> (small) program that reproduces the problem.
>
> Quoting 
> :
>
>> Hello,
>>
>> I eventually have found that the planes are being taken in the right way
>> by dereferencing the iterator, but the program is failing in giving the
>> right envelope, and giving an unexplainable exception, I started to
>> believe that the algorithm has a problem... here's the part of the code,
>> where P is a closed polyhedron object
>>
>>
>>     for(plane_it = P.planes_begin(); plane_it !=
>> P.planes_end();++plane_it)
>>     {
>>         planes.push_back(Surface_3(*plane_it));
>>         cout<<*plane_it<<endl;
>>     }
>>
>>     /*
>>     //this is a part where the example inserted the points
>>     planes.push_back (Surface_3(Plane_3(-1, 0, 1, 0)));
>>     planes.push_back (Surface_3(Plane_3(0, 1 , 1, 0)));
>>     planes.push_back (Surface_3(Plane_3(1, 0, 1,  0)));
>>     */
>>
>>       // Compute and print the minimization diagram.
>>     Envelope_diagram_2      min_diag;
>>
>>     CGAL::lower_envelope_3 (planes.begin(), planes.end(), min_diag);
>>
>>     std::cout << std::endl << "The minimization diagram:" << std::endl;
>>     print_diagram (min_diag);
>>
>>     // Compute and print the maximization diagram.
>>     Envelope_diagram_2      max_diag;
>>
>>     CGAL::upper_envelope_3 (planes.begin(), planes.end(), max_diag);
>>
>>     std::cout << std::endl << "The maximization diagram:" << std::endl;
>>     print_diagram (max_diag);
>>
>> The polyhedron I'm using has like 30 facets or more, and is closed and
>> follow the Euler characteristic, and I could view it using Geomview. So
>> I'm very confused and don't know where the error could be. The exception
>> differs everytime because I'm every time generating a new polyhedron
>> that
>> fulfills the conditions mention. here's the error I'm getting in
>> Terminal:
>>
>> terminate called after throwing an instance of
>> 'CGAL::Precondition_exception'
>>   what():  CGAL ERROR: precondition violation!
>> Expr: cv.has_left()
>> File: /usr/local/include/CGAL/Arr_linear_traits_2.h
>> Line: 682
>> Aborted
>>
>> and here's another one too:
>> terminate called after throwing an instance of
>> 'CGAL::Precondition_exception'
>>   what():  CGAL ERROR: precondition violation!
>> Expr: f == f2
>> File:
>> /usr/local/include/CGAL/Arrangement_2/Arrangement_on_surface_2_impl.h
>> Line: 2639
>> Explanation: The two halfedges must share the same incident face.
>> Aborted
>>
>> This last error I can't understand, what does the envelope thing have to
>> do with the halfedges? I'm giving the program plane equations and it has
>> nothing to do with my polyhedron.
>>
>> Any effort is highly appreciated,
>>
>> Thank you,
>> Samer Afach
>>
>>
>>
>>
>>> Hello programmers,
>>>
>>> I have a question since I'm not a professional C++ programmer. I'm
>>> trying to apply the 3D envelope example 32.3.3 in
>>>
>>> http://www.cgal.org/Manual/last/doc_html/cgal_manual/Envelope_3/Chapter_main.html
>>>
>>>
>>> but I'm taking the planes from a polyhedron, and I have them in the
>>> type
>>> Plane_3 through the iterator Polyhedron::begin() to end(). The example
>>> takes them in the form Surface_3(Plane_3()), how can I do this
>>> transformation? I tried to use std::transform for this but I failed.
>>> The example provides it using the 4 coefficients of a plane, I can see
>>> these coefficients of my Plane_3 object on a cout stream, but I can't
>>> extract them alone one by one.
>>>
>>> Could you please either tell me the correct transformation method for
>>> this or tell me how to extract the coefficients from my Plane_3 object?
>>>
>>> Thank you,
>>> Samer Afach
>>>
>>> -- 
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>>>
>>
>>
>>
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>>
>
>
>