CGAL users discussion list

[Arun Ramasamy <>]

HI Laurent, Thanks for getting back. I want to extract the surface after I triangulate it. But the API to extract the surface into a polyhedron - output_surface_facets_to_polyhedron - fails to extract the surface after this, since it only supports manifold surfaces. By fail I mean the surface looks pretty disjoint - like a bunch of unconnected triangles. Is there a way to get the surface after extracting it as non-manifold? thanks

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From: Laurent Rineau (GeometryFactory) <>
To:
Sent: Thu, June 16, 2011 5:56:35 AM
Subject: Re: [cgal-discuss] Surface Meshing

On jeudi 16 juin 2011 00:30:05 Arun Ramasamy wrote:
> Hello,
> I'm using CGAL's Surface Mesher to extract Isosurfaces from volume
> datasets. The API works many times. However it fails equally often with an
> exception thrown in the method 'private_test_point_conflict_impl' at
> line#248 in
> CGAL/Surface_mesher/Surface_mesher.h. The error message that I get says
> that a 'point is already inserted on surface.' Is it alright to ignore
> this error message (I made CGAL throw exceptions on assertion failures). I
> see this only when the data gets a bit noisy.

On lundi 13 juin 2011 16:08:16 Arun Ramasamy wrote:
> Hi, I'm currently attempting to extract iso-surface from a volume data-set
> using the 3D Surface Mesh Generator API. This API works for some of the
> iso-values. However, it fails for other values and doesn't terminate. It
> seems like it fails when there are outliers for the given iso-value (eg/
> like a sphere inside another sphere).
>
>
> Is it possible to either
> a. Make the algorithm ignore the outliers if it not connected to the
> 'correct' closed surface around the center of the bounding sphere. or
> b. Make the algorithm extract multiple disconnected closed iso-surfaces
> from the data set. or even
> c. Terminate with failure if it detects something wrong with the
> data-set/oracle.
>
> Other ideas are welcome too. Thanks.

Hi Arun,

So far I had not found time to reply to your mail of last Monday. Sorry.

If your 3D image is a bit noisy at the iso-value you specify, then it can be
impossible to create a manifold iso-surface from it. You should use the tag
CGAL::Non_manifold_tag() instead of CGAL::Manifold_tag().

--
Laurent Rineau, PhD
R&D Engineer at GeometryFactory          http://www.geometryfactory.com/
Release Manager of the CGAL Project      http://www.cgal.org/

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