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[Graviton <>]

I am not very sure how to make use of the 
http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Alpha_shapes_2_ref/Class_Alpha_shape_2.html#Cross_link_anchor_1390
classification type  to classify which face belongs to the Alpha Shapes of a
point cloud. In my application I would need to let the user set the alpha
level, so that they could see how that alpha level is changing their terrain
shapes.

So, this is the code that I have; first I would collect all the faces and
store it somewhere. After I know the alpha level set by the user, I would
classify each face and collect the face that is of the classificationtype
interior. 

Here's my code:




void AlphaShapes::Triangulate(list<Point_2> surveyorList,  AlphaShapeMode
Mode, AlphaShapeCg *alphaContainer,  list<list&lt;Point_2>>  &faceList,
list<Number_type> &alphas)
{
        ConvertUtility::ConvertPolyList(surveyorList, SurveyPts);

        //Alpha_shape_2 A(surveyorList.begin(), surveyorList.end(),
100000,(Alpha_shape_2::Mode)Mode);
        Alpha_shape_2 *A =new Alpha_shape_2(surveyorList.begin(),
surveyorList.end(), 100000,(Alpha_shape_2::Mode)Mode);
        alphaContainer->AlphaShape = A;


        faceList.clear();

        Face_iterator fit;
        for(fit=A->finite_faces_begin(); fit!=A->finite_faces_end(); ++fit)
        {
                list<Point_2> face;
                face.push_back(fit->vertex(0)->point());
                face.push_back(fit->vertex(1)->point());
                face.push_back(fit->vertex(2)->point());

                faceList.push_back(face);
        }


        for(int i=0; i< A->number_of_alphas(); i++)
        {
                alphas.push_back(A->get_nth_alpha(i));
        }
        
        }
        
        void AlphaShapes::GetShapes(Alpha_shape_2 *A,
list<Alpha_shape_2::Classification_type> &classType, double alphaLevel)
{

        classType.clear();
                Face_iterator fit;
        for(fit=A->finite_faces_begin(); fit!=A->finite_faces_end(); ++fit)
        {


                          Alpha_shape_2::Classification_type classType2 = 
A->classify(fit);
                          
classType.push_back((AlphaShapeClassificationType)classType2);
        }


}


The problem is that when I examine classType for my sample project, it is
always EXTERIOR for all the faces, regardless of what the alphaLevel is.
This is not what I want, as I want to see that if I decrease the alpha
level, the faces I collect should be less and less; and if I increase the
alpha level, the faces I collect should be more and more until the whole
face collection approaches the convex hull of the points.

Anything I do wrong?

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