CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

You can iterator over vertices using
[nef.vertices_begin(), nef.vertices_end()[


http://doc.cgal.org/latest/Nef_3/classCGAL_1_1Nef__polyhedron__3.html#af91bdaaa2b4324250d1bc15a38d30787

You can also get access to the half-facets:
[nef.halffacets_begin(), nef.halffacets_end()[

http://doc.cgal.org/latest/Nef_3/classCGAL_1_1Nef__polyhedron__3.html#a92eca2af31def19d96363904ce95881b

Sebastien.

On 11/04/2016 12:44 AM, Vahid Azizi wrote:
> Sorry again! no, i don't want to calculate the symmetric difference.
> I just want to calculate the difference, for clarification i uploaded
> another image
> <https://drive.google.com/file/d/0B6aDrBbewOPBSkJKOHkzSW1vVXc/view?usp=sharing>
> which shows what i want. The bold black part which marked with an arrow
> is the part that i want to extract if there is any.
>
> do you have any suggestion for raised issue with explained method in
> earlier email?
>
> Also i tried another way with nef_polyhedron, first i create  convex
> hull for my two point sets, then convert them to nef_polyhedron and
> apply difference operator over them, the code
> <https://docs.google.com/document/d/1HKOlX4bWXEaJX3lmmwGtt67b07nu22yyPkJJ192iJko/edit?usp=sharing>
> is uploaded here. i want to convert back the result of nef_polyhedron to
> polyhedron but i get error about preconditions. I tried sample code in
> the CGAL doc and the result nef couldn't pass is_simple() function. I
> need just the vertices of extracted part. does not passing is_simple()
> function mean the result of operator is not correct? if it is correct,
>  is there any way to get the vertices even without converting back to
> polyhedron?
>
> Thank you so much!
>
> Best,
> Vahid
>
>
> On Thu, Nov 3, 2016 at 9:43 AM, Sebastien Loriot (GeometryFactory)
> <
>  
> <mailto:>>
>  wrote:
>
>
>     Sorry, it is still not clear to me what you want to do.
>     I don't know if you want to compute the symmetric difference
>     or something else.
>
>     Sebastien.
>
>     On 11/02/2016 07:00 AM, Vahid Azizi wrote:
>
>         Sorry, i tried to keep the message so short. anyway, I am doing
>         following steps:
>
>         1) I have some points which they are supposed to be a
>         polyhedron, It is
>         the result by delaunry triangulation over these points: polyhedron
>         
> <https://drive.google.com/file/d/0B6aDrBbewOPBUTlZaHlSYmsxWkE/view?usp=sharing
>         
> <https://drive.google.com/file/d/0B6aDrBbewOPBUTlZaHlSYmsxWkE/view?usp=sharing>>
>
>         2) i have another set of points which they are supposed to be a
>         plane,
>         after delanury triangulation over this set I have: plane
>         
> <https://drive.google.com/file/d/0B6aDrBbewOPBSUlVdTdlUUl2XzQ/view?usp=sharing
>         
> <https://drive.google.com/file/d/0B6aDrBbewOPBSUlVdTdlUUl2XzQ/view?usp=sharing>>
>
>         3) in last step i want to find the subsurface of the plane which
>         is not
>         in intersection with polyhedron. My idea here is to iterate over all
>         triangles and keep all intersection points in a list, then i can
>         create
>         a convex hull out of intersection points. So, i have the subsurface
>         which is in intersection with polyhedron. I did these steps for
>         another
>         purpose before and it works. I didn't try to extract the subsurface
>         which is not in intersection but there must be a way for that.
>
>         Now, the problem is with explained idea as you see in this image
>         
> <https://drive.google.com/file/d/0B6aDrBbewOPBV2J2VktfUEFpN0U/view?usp=sharing
>         
> <https://drive.google.com/file/d/0B6aDrBbewOPBV2J2VktfUEFpN0U/view?usp=sharing>>,
>         intersection function doesn't return any intersection points for
>         upper
>         red triangle(upper part of the plane) . But there are two
>         intersection
>         points for down red triangle which are marked with blue star. As
>         i spent
>         some time for finding the reason it seems the problem is this
>         triangle
>         doesn't have any intersection with edges of triangles in
>         polyhedron. I
>         think if i could change the resolution of triangulation i could
>         solve
>         this problem. If i have more fined triangles in polyhedron with high
>         probability there will be intersection with their edges. As i
>         searched
>         it seems there is not any option for modifying resolution of
>         triangulation. Also the fig file for this issue is uploaded here
>         
> <https://drive.google.com/file/d/0B6aDrBbewOPBR1RtVUE5ZkZVUE0/view?usp=sharing
>         
> <https://drive.google.com/file/d/0B6aDrBbewOPBR1RtVUE5ZkZVUE0/view?usp=sharing>>,
>         maybe it could give you better view.
>
>         My questions are:
>
>         Is there any better way to find the subsurface of the plane
>         which is not
>         in intersection with polyhedron? Here just assume i have to two 3D
>         polyhedrons which i want to find the part which doesn't have
>         intersection.
>
>         if there is not any better way, how could i solve the current issue?
>
>         Thanks in advance,
>         Best,
>
>
>
>         On Tue, Nov 1, 2016 at 3:36 AM, Sebastien Loriot (GeometryFactory)
>         
> <
>  
> <mailto:>
>         
> <mailto:
>  
> <mailto:>>>
>  wrote:
>
>             It is not clear (at least to me) what you are trying to do.
>             What are you looking for? An intersection function for 2
>         triangle soups?
>             A 3D constrained triangulation?
>
>             Sebastien.
>
>             On 11/01/2016 03:40 AM, Vahid Azizi wrote:
>
>                 Hi all,
>
>                 I have a geometry volume and a plane(their vertices),
>         the Delaunry
>                 triangulation is applied on both of them(their
>         vertices). For the
>                 geometry volume i get 16 facets and for the plane i get two
>                 facets. I
>                 need to find intersection between these two. It seems in
>         some
>                 case the
>                 plane which is inside the volume doesn't have
>         intersection with any
>                 facets of volume. I searched for changing resolution of
>                 triangulation
>                 but it seems there is not such a option. I've attached
>         an image
>                 which
>                 depicts the situation and also a fig file which you can
>         rotate
>                 the image
>                 to see what is the problem. The blue stars are intersection
>                 points for
>                 down red triangle.
>
>                 images:
>
>         
> https://drive.google.com/drive/folders/0B6aDrBbewOPBR2gwTE5JZm4yNnc?usp=sharing
>         
> <https://drive.google.com/drive/folders/0B6aDrBbewOPBR2gwTE5JZm4yNnc?usp=sharing>
>
>         
> <https://drive.google.com/drive/folders/0B6aDrBbewOPBR2gwTE5JZm4yNnc?usp=sharing
>         
> <https://drive.google.com/drive/folders/0B6aDrBbewOPBR2gwTE5JZm4yNnc?usp=sharing>>
>
>                 Is there anything that i can do, maybe with resolution
>         or with
>                 intersection or do i need to go with another approach?
>
>                 Thanks in advance!
>
>                 Best,
>                 --
>                 /Vahid/
>
>
>
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>
>
>
>         --
>         /Vahid/
>
>
>
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> --
> /Vahid/