[Gmsh] Quadrangles and Q1 shape functions

[Mikhail Artemyev]

Hi Torquil,

That reminds me the similar problem I had with visualization of solution 
on a rectangular grind in ParaView.
This is the thread: 
http://public.kitware.com/pipermail/paraview/2014-May/031144.html
I'm copying the relevant part of the answer I linked to here:

"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."

Hope this helps.

Best,
Mikhail


On 09/24/2015 11:34 AM, gmsh-request at ace20.montefiore.ulg.ac.be wrote:
> Hi!
>
> I have a MSH file for a mesh of one quadrangle and four associated
> scalar field node values. Looking at the GMSH visualization, it uses two
> triangles to define the function shape inside the quadrangle, and it
> seems to use P1 shape functions within each triangle.
>
> Is it possible to have GMSH not use any triangles for the visualization,
> but instead assume that the scalar field should be represented with Q1
> shape functions inside the quadrangle?
>
> Here is the MSH file, and the screenshot is attached:
>
> $MeshFormat
> 2.2 0 8
> $EndMeshFormat
> $Nodes
> 4
> 1 0.0 0.0 0.0
> 2 1.0 0.0 0.0
> 3 1.0 1.0 0.0
> 4 0.0 1.0 0.0
> $EndNodes
> $Elements
> 1
> 1 3 2 99 2 1 2 3 4
> $EndElements
> $NodeData
> 1
> "A scalar view"
> 1
> 0.0
> 3
> 0
> 1
> 4
> 1 0.0
> 2 1.0
> 3 0.0
> 4 0.0
> $EndNodeData
>
> Best regards and thanks,
> Torquil S?rensen