Hi, I've been successfully meshing a 2D domain with the CDT as per I've been using an outer domain constraint, and have now started to add interior constraints (lines that represent rivers that should be not crossed by triangles). This works as expected. However, when I enable lloyd optimization I have the following error: Running 1 Lloyd iterations... CGAL error: assertion violation! Expression : do_intersect(line, m_cdt.segment(face>blinding_constraint())) File : /usr/local/include/CGAL/Constrained_voronoi_diagram_2.h Line : 392 Explanation: Refer to the bugreporting instructions at http://www.cgal.org/bug_report.html libc++abi.dylib: terminating with uncaught exception of type CGAL::Assertion_exception: CGAL ERROR: assertion violation! Expr: do_intersect(line, m_cdt.segment(face>blinding_constraint())) File: /usr/local/include/CGAL/Constrained_voronoi_diagram_2.h Line: 392 When I use the same domain *without* the interior constraints, the lloyd optimization works as expected. I've been unable to figure out what is going wrong based on this error message and would appreciate any insight Cheers Chris 
Hi Chris,
thanks for your report. First, I have one question : did you insert the interior constraints before running the mesher (I mean the refinement step), or after? Can you please send some code and data to help me reproduce the issue? The use case you mention has been tested already, so I would need your data. Best regards, Jane. Le 23/02/2018 à 00:25, Chris Marsh a écrit : > Hi, > > I've been successfully meshing a 2D domain with the CDT as per > https://doc.cgal.org/latest/Mesh_2/index.html > > I've been using an outer domain constraint, and have now started to > add interior constraints (lines that represent rivers that should be > not crossed by triangles). > > This works as expected. > > However, when I enable lloyd optimization I have the following error: > > Running 1 Lloyd iterations... > CGAL error: assertion violation! > Expression : do_intersect(line, > m_cdt.segment(face>blinding_constraint())) > File : /usr/local/include/CGAL/Constrained_voronoi_diagram_2.h > Line : 392 > Explanation: > Refer to the bugreporting instructions at > http://www.cgal.org/bug_report.html > libc++abi.dylib: terminating with uncaught exception of type > CGAL::Assertion_exception: CGAL ERROR: assertion violation! > Expr: do_intersect(line, m_cdt.segment(face>blinding_constraint())) > File: /usr/local/include/CGAL/Constrained_voronoi_diagram_2.h > Line: 392 > > When I use the same domain *without* the interior constraints, the > lloyd optimization works as expected. > > I've been unable to figure out what is going wrong based on this error > message and would appreciate any insight > > Cheers > Chris  Jane Tournois, PhD R&D Engineer at GeometryFactory http://www.geometryfactory.com/  You are currently subscribed to cgaldiscuss. To unsubscribe or access the archives, go to https://sympa.inria.fr/sympa/info/cgaldiscuss 
Ok this is odd. I made some changes this morning (nothing related to my
constraint code) and recompiled, problem is gone. I can run the domain with lloyd optimization without issue. However, the resulting "optimized" mesh is of poor quality. Many small, thin (nonDelauany) triangles are present along the constraint (circled in red). I've attached an image to show what I mean where I ran max of 100 lloyd iterations. Is this expected behaviour? All the other meshes I run lloyd iterations on produce high quality meshes. <http://cgaldiscuss.949826.n4.nabble.com/file/t375307/File_001.png>  Sent from: http://cgaldiscuss.949826.n4.nabble.com/  You are currently subscribed to cgaldiscuss. To unsubscribe or access the archives, go to https://sympa.inria.fr/sympa/info/cgaldiscuss 
I see the bad triangles, but I don't understand where the constraints
are, on your figure. Can you please highlight them? Le 24/02/2018 à 01:00, chrism a écrit : > Ok this is odd. I made some changes this morning (nothing related to my > constraint code) and recompiled, problem is gone. I can run the domain with > lloyd optimization without issue. However, the resulting "optimized" mesh is > of poor quality. Many small, thin (nonDelauany) triangles are present along > the constraint (circled in red). I've attached an image to show what I mean > where I ran max of 100 lloyd iterations. Is this expected behaviour? All the > other meshes I run lloyd iterations on produce high quality meshes. > > <http://cgaldiscuss.949826.n4.nabble.com/file/t375307/File_001.png> > > > >  > Sent from: http://cgaldiscuss.949826.n4.nabble.com/ >  Jane Tournois, PhD R&D Engineer at GeometryFactory http://www.geometryfactory.com/  You are currently subscribed to cgaldiscuss. To unsubscribe or access the archives, go to https://sympa.inria.fr/sympa/info/cgaldiscuss 
Ah, sorry. Please find the comparison as presented above with the constraint
shown in red. <http://cgaldiscuss.949826.n4.nabble.com/file/t375307/lloyd.png> As I cannot attach a large image, it may be difficult to see exactly? If so, I have paraview compatible VTU files as well as the triangulation and constraint in ESRI shape files (shp) to load into a GIS, such as qGIS.  Sent from: http://cgaldiscuss.949826.n4.nabble.com/  You are currently subscribed to cgaldiscuss. To unsubscribe or access the archives, go to https://sympa.inria.fr/sympa/info/cgaldiscuss 
Hi Chris, I understand what you mean. You can have a look at this paper for more details on our
algorithm : The triangles that are called "blind" (meaning that their
circumcenter is on the other side of a constrained edge) can
hardly have a good shape without refining the associated
constrained edge. If you want better shaped triangles close to constrained edges, they should be refined using the Delaunay_mesh_size_criteria_2 [1]. Also note that the Lloyd smoothing algorithm is enriched with a sizing field that locally preserves the mesh density through iterations. So, the vertices that are close to constraints should remain close to constraints. It avoids creating needleshaped triangles next to constraints. Best regards, Jane.
[1]
https://doc.cgal.org/latest/Mesh_2/classCGAL_1_1Delaunay__mesh__size__criteria__2.html Le 26/02/2018 à 18:06, chrism a écrit :
Ah, sorry. Please find the comparison as presented above with the constraint shown in red. <http://cgaldiscuss.949826.n4.nabble.com/file/t375307/lloyd.png> As I cannot attach a large image, it may be difficult to see exactly? If so, I have paraview compatible VTU files as well as the triangulation and constraint in ESRI shape files (shp) to load into a GIS, such as qGIS.  Sent from: http://cgaldiscuss.949826.n4.nabble.com/  Jane Tournois, PhD R&D Engineer at GeometryFactory http://www.geometryfactory.com/ 
In reply to this post by chrism
Le 23 févr. 2018 00:26, "Chris Marsh" <[hidden email]> a écrit :

I will read the paper, but I think this makes sense. I will just use fewer/no
iterations then! I'll let you know if I run into that strange error again. Thanks very much Cheers Chris  Sent from: http://cgaldiscuss.949826.n4.nabble.com/  You are currently subscribed to cgaldiscuss. To unsubscribe or access the archives, go to https://sympa.inria.fr/sympa/info/cgaldiscuss 
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