[Dune] Re: Notification from Dune

[Christian Engwer]

Hi Oliver,

On Wed, Oct 18, 2006 at 03:59:02PM +0200, Oliver Sander wrote:
> No, it is not a problem of the library.  For the library it is
> reasonable to expect that its input surface is consistently
> oriented so it can compute consistent normals.
> 
> Consider the reference quad.
> 
> 2----3
> |    |
> |    |
> 0----1
> 
> I want to extract the boundary and hand it over to my library.
> Ideally I would extract
> 
> (0,1)
> (1,3)
> (3,2)
> (2,0)
> 
> so the library knows that when it goes from p to q on (p,q), the
> outward normal is pointing to its right.  But instead the
> reference element yields
> 
> (0,1)  (outward normal to the right)
> (1,3)  (   "      "    "   "   "   )
> (2,3)  (outward normal to the left)
> (0,2)  (   "      "    "   "   "  )

But if the Dune orientation would be:

2----3
|    |
|    |
0----1

with the edges
(1,0)
(3,1)
(2,3)
(0,2)

Your library would also assume a wrong outward normal. Or am I
mistaken?

Christian