[Gmsh] problems with postprocessing format ($NodeData section)

[Christophe Geuzaine]

Paulo Vieira wrote:
> Hello all,
> 
> I'm having some problems in understanding the postprocessing sections of 
> Gmsh's native file format (section 9 of the manual,
> http://geuz.org/gmsh/doc/texinfo/gmsh-full.html#SEC62 ).
> 
> Consider this simple handmade example constituted by 6 nodes and 2 
> elements (see the attached file, or at the bottom of the
> message).
> 
> The mesh sections are fine ($Nodes, $Elements). Now I want to add a 
> $NodeData section. The example I made doesn't read if
> the $NodeData section is present ("Filling PViewDataGModel... Could not 
> read data in msh file" - see the log attached).
> 
> Questions:

Hi Paulo,

> 
> 1- Do the string tags need to have a "" (or '') ?

enclosed in "..."

> 
> 2- According to the manual,
> 
> "By default the first string-tag is interpreted as the name of the 
> post-processing view, and the second as the name of the
> interpolation scheme."
> 
>  Is this second tag mandatory? Where can I find more information about 
> the interpolation schemes available?

It's still being interfaced. I've removed the reference to this from the 
doc for now.

> 
> 3- What is the purpose of the real-tags in the postprocessing sections?
> 

The first tag is interpreted as a time value associated with the dataset.

> 
> It seems the problem with my example is related to one or more of these 
> issues, but I don't know what to do. I think a
> simple example in the manual would make things much clearer.

Indeed. The format is still quite new and we haven't had the chance to 
add examples yet.

Here's an annotated version of your file:

$NodeData
1              // 1 string tag:
"a_string_tag" //   the name of the view
1              // 1 real tag:
0              //  time value == 0
3              // 3 integer tags:
0              //  time step == 0 (time steps always start at 0)
1              //  1-component field (scalar) (only 1,3,9 are valid)
6              //  6 values follow:
1 0.0          //  value associated with node 1 == 0.0
2 0.1          //  ...
3 0.2
4 0.0
5 0.2
6 0.4
$EndNodeData


> 
> Thanks for your help.
> 
> Paulo
> 
> 
> 
> $MeshFormat
> 2.0 0 8
> $EndMeshFormat
> 
> $Nodes
> 6
> 1 0 0 0
> 2 1 0 0
> 3 1 1 0
> 4 0 1 0
> 5 2 0 0
> 6 2 1 0
> $EndNodes
> 
> $Elements
> 2
> 1 3 0 1 2 3 4
> 2 3 0 2 5 6 3
> $EndElements
> 
> $NodeData
> 1
> "a_string_tag"
> 1
> 0
> 4
> 1
> 2
> 6
> 1
> 1 0.0 0.0
> 2 0.3 0.1
> 3 0.3 0.2
> 4 0.0 0.0
> 5 0.5 0.2
> 6 0.6 0.4
> $EndNodeData
> 
> 
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> 
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-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine