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[Samer Afach <>]

Exactly! That's what I'm looking for actually! But could you please tell
me how to implement it? does the envelope class have such a function?

Thank you,
Samer



 wrote:
> If you are looking for a function that accepts a polyhedron and a
> point in the plane and returns the point on the lower envelope of the
> polyhedron, the vertical projection of which coincides with the input
> point, then you can implement it using the existing functionality.
> Otherwise, I don't understand your question.
>
> Quoting "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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>>>>> https://lists-sop.inria.fr/wws/info/cgal-discuss
>>>>>
>>>>
>>>>
>>>>
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>>>>
>>>
>>>
>>>
>>
>>
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>
>
>