CGAL users discussion list

[chrism <>]

It's the same rotation to each vertex, regardless of face.

On Jul 26, 2014 2:23 AM, "andreas.fabri [via cgal-discuss]" <[hidden email]> wrote:

Hello,

Is it the same rotation for all vertices?
Even then due to numerical issues collinear vertices
might become non-collinear.

Or do you apply different rotations to the
vertices?

Or do you even apply a different rotation for
a vertex, depending on the face you are in?

andreas

On 26/07/2014 01:58, chrism wrote:

> Yes that's my concern that it breaks something in a subtle way. I'll try
> this and see what happens though. Thanks!
>
> On Jul 25, 2014 5:14 PM, "Sylvain Pion-3 [via cgal-discuss]" <[hidden
> email] </user/SendEmail.jtp?type=node&node=4659616&i=0>> wrote:
>
>     I believe it changes nothing else.  But of course be careful, this
>     violates Delaunay invariants, and if you use the Delaunay hierarchy,
>     things can get funny.
>     If you can find a different way to achieve what you want without
>     resorting to such a hack, it would be better.
>
>
>     2014-07-25 16:01 GMT-07:00 chrism <[hidden email]
>     <http://user/SendEmail.jtp?type=node&node=4659615&i=0>>:
>
>         And that will not change the triangulation? Not sure how I
>         missed that, thanks.
>
>         On Jul 25, 2014 4:52 PM, "Sylvain Pion-3 [via cgal-discuss]"
>         <[hidden email]
>         <http://user/SendEmail.jtp?type=node&node=4659614&i=0>> wrote:
>
>             Use set_point() to change the point of a vertex :
>             http://doc.cgal.org/latest/Triangulation_2/classTriangulationVertexBase__2.html

>

>
>
>             2014-07-25 15:33 GMT-07:00 chrism <[hidden email]
>             <http://user/SendEmail.jtp?type=node&node=4659613&i=0>>:
>
>                 I need to apply a rotation to each triangle in my
>                 Delauny (2D) triangulation.
>                 To do this, I calculate the rotation to move each
>                 triangle's vertex into the
>                 new coordinate system. Because I need to perform
>                 triangle-triangle
>                 intersection in this new coordinate system I need to
>                 update the x,y,z values
>                 at each vertex to the new x',y',z' values. Critically
>                 though, I need to
>                 maintain the triangles (despite the fact they will no
>                 longer be Delaunay) --
>                 therefore removal/insert doesn't work.
>
>                 Therefore, what would be the best way forward to modify
>                 the vertex's x,y,z
>                 values?
>
>                   Ideally I'd do something like:
>
>                 Delaunay prj(original_tri);
>                      for (triangulation::Finite_faces_iterator fit =
>                 prj->finite_faces_begin(); fit !=
>                 prj->finite_faces_end(); ++fit)
>                      {
>                          //interpolate the station data to the current
>                 element
>                          triangulation::Face_handle face = fit;
>
>                          vert(0) = face->vertex(0)->point().x();
>                          ver(1) = face->vertex(0)->point().y();
>                          vert(2) = face->vertex(0)->point().z();
>
>                          rot_vert = rotation(vert);
>                          face->vertex(0)->set_x(rot_vert(0));
>                          face->vertex(1)->set_x(rot_vert(1));
>                          face->vertex(2)->set_x(rot_vert(2));
>
>
>                 .....
>
>
>                 Thanks.
>
>
>
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--
Andreas Fabri, PhD
Chief Officer, GeometryFactory
Editor, The CGAL Project

phone: <a href=""tel:%2B33.492.954.912"" value="+33492954912" target="_blank">+33.492.954.912    skype: andreas.fabri

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