[Gmsh] Cylinder structured grid problem

[Geordie McBain]

2011/3/19  <gmsh at praveen.e4ward.com>:
> Thanks. That worked.
> I have  a problem with areas. I am using the circle grid with deal.II. Its a
> 2-d problem so I generate only mesh in z=0. deal.II is saying that areas are
> negative.
> In the attached grid, Ruled Surface 1 is oriented ccw but the other Ruled
> Surface 5, 10 are cw. I think this is causing the problem. Is there a way to
> fix this ?

Yes, I see what you mean.  It isn't just deal.II thinking this, as can
be demonstrated by setting Geometry.Normals=100 in Gmsh and then
slightly rotating the view away from the z-axis (as in the attached
normals.png).

I guess this is a property of Symmetry (which kind of makes sense
since clocks turn anticlockwise in mirrors).  I suppose the quick
answer is not to use Symmetry in two-dimensional work.  In
three-dimensions, for the two ends of the cylinder, this behaviour
would be correct.

Of course there are many ways of generating the example file you sent
without using Symmetry (Extrude, Rotate, For, ...); actually I'd
probably just do it long-hand, I think, but then you've probably
simplified this to be a convenient example.
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