[Gmsh] gmsh BSpline issue

[Christophe Geuzaine]

Hi Arjen - Thanks for your mail: that's definitely a bug. We will 
investigate.

Arjen Terwisscha van Scheltinga wrote:
> Hi,
> 
> I'm currently using gmsh to build a high resolution mesh for the 
> Canadian Arctic Archipellago (CAA). In order to do this, I have 
> represented all the islands in the CAA as closed BSplines, and in order 
> get sufficient resolution I use attractors to define the background 
> field. For small characteristic lengths the 2D meshing produces weird 
> results - which I don't get.
> 
> To better understand why, and to make sure its not a issue of 
> geometrical model for the CAA, I've investigated this issue in a very 
> simplified geometry. Same problem persists. (I've attached a two pdfs of 
> the geometry and mesh, as well as the .geo file). The geometry is 
> basically two islands defined by closed BSPlines in a circle. The 
> problem is the 'teardrop'-shaped areason the left-bottom side of the 
> 'islands', which is where the beginning and end of the BSPline are 
> joined together.
> Some further observations:
> - it seems to be independent of the meshing algorithm;
> - is works OK if I use ordinary splines;
> - rearranging the control points of the BSpline, don't help - it just 
> moves the problem to another area, which still coincides with the 
> begin/end point of the BSpline.
> - in this area close to the begin/end point is generates triangles 
> always the begin/end point as one of the three points.
> 
> To me it looks like main problem is the results of the 
> geometrical/control begin/end point of the BSpline is not at the same 
> position as the 'physical' begin/end point. The 1D mesh looks OK.
> 
> Anyway, don't know if I can classify this as a bug - if I do something 
> obviously wrong do tell me, but is seems to me to be to robust to be a 
> simple mistake on my side. Any ideas? I hope there is a quick fix.
> 
> Apart from this issue, I'm quite happy with gmsh.
> 
> With regards, Arjen
> 
> ==================================================
> Arjen Terwisscha van Scheltinga
> 
> Email: arjen.terwisschavanscheltinga at ualberta.ca
> Office: Tory 3-129    Phone: (780) 492-3564
> 
> Department of Earth and Atmospheric Sciences
> 1-26 Earth Science Building, University of Alberta
> Edmonton, Alberta
> T6G 2E3, Canada
> 
> 
> 
> 
> 
> 
> ------------------------------------------------------------------------
> 
> _______________________________________________
> gmsh mailing list
> gmsh at geuz.org
> http://www.geuz.org/mailman/listinfo/gmsh


-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine