[Paraview] Quadrangles and Q_1,1 basis functions

[Kaushik Kulkarni]

Hey Torquil Sørensen,
You will get the desired solution once you change "POINT_DATA 9" to
"CELL_DATA 4".
And then similarly specifying the data in each of the cell. In this case I
suppose the .vtk file for you should be-


# vtk DataFile Version 2.0
Exported by getfem++
ASCII
DATASET UNSTRUCTURED_GRID
POINTS 9 float
 0 0 0
 0.5 0 0
 0 0.5 0
 0.5 0.5 0
 1 0 0
 1 0.5 0
 0 1 0
 0.5 1 0
 1 1 0

CELLS 4 20
 4 0 1 3 2
 4 1 4 5 3
 4 2 3 7 6
 4 3 5 8 7

CELL_TYPES 4
 9
 9
 9
 9

CELL_DATA 4


SCALARS scalarField float 1
LOOKUP_TABLE default
 0 0 0 1

Cheers,
Kaushik



On Tue, Sep 22, 2015 at 7:56 PM, Torquil Macdonald Sørensen <
torquil at gmail.com> wrote:

> Hi!
>
> I have defined a 2d quadrangle mesh consisting of 2x2 elements, with
> Q_1,1 basis functions in GetFEM++, and exported an example function to
> ASCII VTK format. The only node at which the example function is nonzero
> is the middle one.
>
> When I open the VTK file in Paraview, it looks as if it has used some
> kind of triangle interpolation. Instead of its support being the entire
> mesh, it has become zero near two opposite domain corners. In
> particular, the result should have been 90-degree rotation symmetric
> about the centre node.
>
> How do I get Paraview to display this Q_1,1 function correctly, or at
> least without it seemingly being interpolated onto a triangular mesh?
>
> I'm using Paraview 4.3.1 and the ASCI VTK file generated by GetFEM++ is:
>
> # vtk DataFile Version 2.0
> Exported by getfem++
> ASCII
> DATASET UNSTRUCTURED_GRID
> POINTS 9 float
>  0 0 0
>  0.5 0 0
>  0 0.5 0
>  0.5 0.5 0
>  1 0 0
>  1 0.5 0
>  0 1 0
>  0.5 1 0
>  1 1 0
>
> CELLS 4 20
>  4 0 1 3 2
>  4 1 4 5 3
>  4 2 3 7 6
>  4 3 5 8 7
>
> CELL_TYPES 4
>  9
>  9
>  9
>  9
>
> POINT_DATA 9
>
>
> SCALARS scalarField float 1
> LOOKUP_TABLE default
>  0 0 0 1 0 0 0 0 0
>
> Thanks and best regards
> Torquil Sørensen
>
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