[Gmsh] gmsh BSpline issue

[Arjen Terwisscha van Scheltinga]

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

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