[Dune] Gridcheck asks for geometry.local() outside the element?

[Aleksejs Fomins]

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Dear Jö,

For curvilinear geometries global->local mapping is not defined outside the element.

If I understand correctly, if someone asks me for a global coordinate strongly outside the element, then I could return a whatever local coordinate that is strongly outside the element, eg (-100, 0, 0). I hope that people only care if the coordinate is inside or outside the element and do not care of the actual local coordinate if they know it is outside.

Because if this is not the case, we have a serious design problem.

Thanks for your reply
Aleksejs

On 26/02/15 17:25, Jö Fahlke wrote:
> Am Thu, 26. Feb 2015, 16:58:38 +0100 schrieb Aleksejs Fomins:
>> I am now trying to make the gridcheck run with curvilinear grid.
>>
>> It seems that at some point gridcheck calls the geometry.local() method for one of tetrahedra in the provided mesh. And it calls the method with a global coordinate that is clearly outside the element. I previously assumed this was an illegal action, so I throw an error there...
>>
>> Questions:
>> 1) Is this expected behaviour of gridcheck?
>> 2) If yes, what is the expected return value?
>> 3) If no, then the problem is elsewhere. To search for it, I need debug output. Does gridcheck have debug output and if yes how to switch it on?
> 
> Without having looked at what the grid check does: It is kind-of legal to
> stuff a coordinate outside the element into local().  This can happen
> e.g. during a hierarchic search, when you try to find the element that
> contains a certain Coordinate.  You (as a grid implementor) can
> however declare that this is not supported for your grid, as hierarchic search
> is just a utility class.
> 
> Another instance where local() receives outside coordinates is due to rounding
> errors.  You should allow that, but you can take advantage of the fact that
> these coordinate will only be very slightly outside.
> 
> If you can smoothly extend the local() mapping to the outside of the element,
> then you should return the result according to this smooth extension.
> Otherwise you probably already have singularities on the boundary of the
> element, and we have to think about that some more.
> 
> Regards,
> Jö.
> 
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