CGAL users discussion list

[Vahid Azizi <>]

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 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 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) <> 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>

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>

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>,
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>,
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:>> 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>

        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/



    --
    You are currently subscribed to cgal-discuss.
    To unsubscribe or access the archives, go to
    https://sympa.inria.fr/sympa/info/cgal-discuss

    <https://sympa.inria.fr/sympa/info/cgal-discuss>





--
/Vahid/

--
You are currently subscribed to cgal-discuss.
To unsubscribe or access the archives, go to
https://sympa.inria.fr/sympa/info/cgal-discuss

--

Vahid