[Dune] tranformed geometry across periodic boundaries

[Matteo Semplice]

Hi dune,
     I think I need some explanation on the exact meaning of the phrase 
"transformed geometry" in the documentation of Dune::Intersection 
<http://www.dune-project.org/doc/doxygen/dune-grid-html/class_dune_1_1_intersection.html#_details>

(By the way, the Detailed Description mentions a method "outer()" which 
is not listed in the interface, so I assume that it means "outside()"...)

Say I have a 2d grid with 9 1x1 cells organized as follows

7,8,9
4,5,6
1,2,3

so cell 1 has center at [.5,.5], cell 2 at [1.5,.5] and so on.
Suppose also that the x direction have periodic boundary conditions, 
i.e. my dgf file has the section

PERIODICFACETRANSFORMATION
1 0 , 0 1 + 3 0
#

 From the phrase "outer() cell has a periodically transformed geometry 
(so that one does not see a jump or something like that)" in the section 
on periodic boundaries, I would expect that

if the intersection "face" is the left side of cell 1, and I do

EntityPointer pOut = face.outside();
Entity out = *pOut;

then mapper(out) points me to data related to cell 3, but that
out->geometry().center()
returned [-0.5,0.5], so that effetively I would see the data of cell 3 
as if they were at the left of cell 1 and a PDE code does not need to 
know about the boundary transformation.

As this is not the case (out->geometry().center() returns [2.5,0.5]) , 
what is the meaning of that phrase?
And, given the current situation, does the grid implementation provide a 
method to transform the [2.5,.5] into [-.5,.5] ?

Best regards,
       Matteo

-- 
Matteo Semplice			Dip. di Matematica
Phone: 011-			Università degli Studi di Torino
Skype: matteosemplice		Via Carlo Alberto, 10 - Torino