CGAL users discussion list

[Markus Eich <>]

Dear all.

I am using CGAL to recover the shape from a 2D point cloud. It works 
fine, except that the result always looks like the screenshot attached. 
This is due to the fact that the points are not ordered alpha shape 
output is not ordered in any way.


Here is the code snipped:

=========================

    for(size_t i=0; i<cloud_ptr->points.size(); i++){

            Eigen::Vector3f p3d(cloud_ptr->points[i].x,
                    cloud_ptr->points[i].y,
                    cloud_ptr->points[i].z);

        // subtract all 3D points with a point in the plane
        // this will move the origin of the 3D coordinate system
        // onto the plane
        p3d = p3d - p0;

        K::Point_2 p2d(p3d.dot(u),p3d.dot(v));
        lp.push_back(p2d);
    }


    // compute alpha shape
    Alpha_shape_2 as(lp.begin(),lp.end());

    // find optimal alpha value

    Alpha_iterator opt = as.find_optimal_alpha(1);
    //as.set_alpha(*opt);
    as.set_alpha(0.01);

    boost::geometry::polygon_2d sorted_poly;

    for(Vertice_iterator it = as.alpha_shape_vertices_begin(); it != 
as.alpha_shape_vertices_end(); it++){
        Alpha_shape_2::Vertex_handle vh = *it;
        append(sorted_poly, 
boost::geometry::make<boost::geometry::point_2d>(vh->point().x(),vh->point().y()));
    }


=========================



How can I convert the points that it is ordered (i.e. that only the 
nearest points are connected) and that it doesn't look like a spider web.


Cheers,

Markus






--
Dipl. Inf. Markus Eich
Researcher

DFKI Bremen
Robotics Innovation Center
Mary-Somerville-Str. 9
28359 Bremen, Germany

Phone: +49 (0)421 17845-4105
Fax:   +49 (0)421 17845-4150
E-Mail: 


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