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Re: [cgal-discuss] Extracting the segments from a Surface Mesh


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  • From: "Sebastien Loriot (GeometryFactory)" <>
  • To:
  • Subject: Re: [cgal-discuss] Extracting the segments from a Surface Mesh
  • Date: Mon, 23 May 2016 17:08:09 +0200
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  • Organization: GeometryFactory

If it does what you want, then yes.

Sebastien.

On 05/23/2016 04:57 PM, Sukhraj Singh wrote:
Okay,

Assuming I don't use connected_components().
And I directly create Polyhedrons from the segments, i.e.

- Iterate through polyhedron.
- Create polyhedron of a segment using Polyhedron_incremental_builder_3.

Is this correct way to do ? Or there is some better approach in CGAL.




On Mon, May 23, 2016 at 1:18 PM, Sebastien Loriot (GeometryFactory)
<

<mailto:>>
wrote:

What I mean is if you need both clusters and segments but want to
save on computation time, you can run the segmentation algorithm to
extract
segments and then clusters using `connected_components()` (instead of
another run of segmentation).

Sebastien.

On 05/22/2016 02:32 PM, Sukhraj Singh wrote:

Thanks for your answer, Sebastien
Do I really need to use connected_components()

I already have the "segment_pmap", where the value is the
segment id to
which that particular face belongs.
And one could parse the Polyhedron and collect all the faces having
particular segment ID.(Of-course I need to check, how to
implement the same)
Is my understanding correct ?



Further, quoting from my previous email:

Two spatially apart areas( i.e. not having
common edges) of a Mesh may fall into same segment, since
they had
comparable SDF values.


I am not sure about it, they of-course may fall into same
cluster, but
may not be to the same segment. In such a case if, faces that don't
share edge, will fall into different segment always, even though
they
were in same cluster, using connected_components() may not be
required ?




On Thu, May 12, 2016 at 6:00 PM, Sebastien Loriot (GeometryFactory)

<

<mailto:>

<mailto:

<mailto:>>>
wrote:

On 05/12/2016 02:16 PM, Sukhraj Singh wrote:

Salut,

The "Triangulated Surface Mesh Segmentation" module
allows one to
segment a surface mesh using the SDF values.
It creates a Property Map which is colorized according
to the
indices,
resulting into segments. Two spatially apart areas(
i.e. not having
common edges) of a Mesh may fall into same segment,
since they had
comparable SDF values.

My question is, how can one extract these segments.
Since I want
to do
further processing on a segment separately. Also I
would like
further
divide a segment, into say sub-segments , where a
sub-segment
will have
faces which are not spatially apart, i.e. a subset
which is having
common edges only.



Set the parameter output_cluster_ids to true when calling the
segmentation function


http://doc.cgal.org/latest/Surface_mesh_segmentation/group__PkgSurfaceSegmentation.html#ga8533ea7b1062ebbabe3bf23fed303f24

If you need also the segments, then set the option to false and
use the function connected_components() considering as
constrained
edges the edges between two faces belonging to different
segments.


http://doc.cgal.org/latest/Polygon_mesh_processing/group__keep__connected__components__grp.html#gabe2052b2281e1e628e68d8fea94be2d9


Sebastien.



Thanks to inform.




P.S. I am a newbie.
--
Sukhraj Singh



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Sukhraj Singh



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