[Paraview] non-symmetric representation of symmetric field

[Magician]

Hi Mikhail,


Yes, that’s because of the triangulation (or tesselation) of surface representations.
Most of the 3D programs including ParaView draw objects as groups of triangles.
That’s depends on today’s 3D rendering pipelines such as OpenGL, DirectX, etc.
Please googling the keywords: ‘vertex shading’

Even though you read your data as structured grid with point values,
ParaView should immediately triangulate all of the rectangles, and interpolating
the values between points of the triangles.

# If you visualize cell values, there are no problem caused by interpolating.

The attached image is one of the solution.
1. read your data
2. make a ‘fine resolution' Plane source with same size to the original (for example, 200x100 structured grid)
3. apply Resample With Dataset filter
The result looks nearly-symmetric for me.


Magician


On May 17, 2014, at 10:40, paraview-request at paraview.org wrote:

> Date: Fri, 16 May 2014 20:40:18 -0500
> From: Mikhail Artemyev <artemiev.mikhail at gmail.com>
> To: paraview at paraview.org
> Subject: [Paraview] non-symmetric representation of symmetric field
> Message-ID: <5376BE02.7050800 at gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"; Format="flowed"
> 
> Dear all,
> 
> Here is a minimal example of values distributed over a mesh:
> 
> 0------0------0------0------0
> |        |        |         |        |
> 0----0.5---0.75---0.5-----0
> |        |        |         |        |
> 0------0------1------0------0
> 
> To visualize this field I wrote a .vts file:
> 
> <?xml version="1.0"?>
> <VTKFile type="StructuredGrid" version="0.1" byte_order="LittleEndian">
>   <StructuredGrid WholeExtent="1 5 1 3 1 1">
>     <Piece Extent="1 5 1 3 1 1">
>       <PointData Scalars="scalars">
>         <DataArray type="Float64" Name="sol_" format="ascii">
> 0 0 1 0 0 0 0.5 0.75 0.5 0 0 0 0 0 0
>         </DataArray>
>       </PointData>
>       <Points>
>         <DataArray type="Float64" NumberOfComponents="3" format="ascii">
> 0 0 0
> 1 0 0
> 2 0 0
> 3 0 0
> 4 0 0
> 0 1 0
> 1 1 0
> 2 1 0
> 3 1 0
> 4 1 0
> 0 2 0
> 1 2 0
> 2 2 0
> 3 2 0
> 4 2 0
>         </DataArray>
>       </Points>
>     </Piece>
>   </StructuredGrid>
> </VTKFile>
> 
> The visual representation of this field, however, doesn't look symmetric 
> (a figure is attached),
> although the values are symmetric with respect to a Y-axis crossing the 
> center of the domain.
> 
> Could you please shed some light on where I am wrong -
> in my understanding of visualization technique, or in a way I pass the 
> data to ParaView?
> I use ParaView 4.1.0 64-bit, Linux.
> 
> Thank you.
> Best regards,
> Mikhail
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