[Gmsh] Diplaying of Vector fields

[Christophe Geuzaine]

On 12 Jun 2013, at 23:13, Matthias Lang <Lang_Matthias at gmx.de> wrote:

> Hi Christophe,
> 
> when I select "Aspect->Glyph location = Vertex (instead of Barycenter),
> then some vectors are shown.
> 
> Enclosed you can find a small file "js.pos" where the effect can be demonstrated.
> 

Hi Matthias,

Looking at the dataset, the behavior is actually "normal". Here's what happens:

* min/max=1 is correctly computed from the original dataset (all vectors have a norm = 1)

* displaying the values at the nodes does shows all the values (as expected)

* displaying the values at the barycenter of the elements uses average values; due to the nature of the vector field, the average value over one cell is != 1 (due to the rotation), hence the vectors are not displayed

Maybe we should change the test and display the value at the barycenter if any of (or all ?) the nodal values are within the range?

Re-attaching the file so others can provide suggestions...

Christophe

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> btw.:
> I used the most recent gmsh version:
> Info    : Gmsh version   : 2.7.2-svn
> Info    : Build OS       : Linux
> Info    : Build date     : 20130612
> 
> Regards
> Matthias Lang
> 
> Am 12.06.2013 17:24, schrieb Christophe Geuzaine:
>> 
>> Hi Matthias - My guess is that there is some roundoff error and we don't use a large enough tolerance. Could you
>> 
>> * try to see if the same problem persists when selecting "Aspect->Glyph location = Vertex" in Tools->Options->View
>> 
>> * send me a small .pos file with a dataset that triggers the issue ?
>> 
>> Many thanks,
>> 
>> Christophe
>> 
>> On 11 Jun 2013, at 07:39, Matthias Lang <Lang_Matthias at gmx.de> wrote:
>> 
>>> Hello everybody,
>>> 
>>> I defined in a getdp *.pro file for an example a current (1Amp) in a torus.
>>> I expected to see a vector field with vector arrows of the same length.  But in the coressponding view no vector field were seen (and no error message) And the displayed scale showed a range from 1 to 1
>>> 
>>> Few hours later...
>>> 
>>> I found out, that when I set the  range mode in Menu Options //General
>>> to "Custom" and the range form Min=0 to Max=1 --> then the expected vectorfield is shown.
>>> But when I set the range from Min=1 Max = 1 -  nothing ist shown again.
>>> 
>>> My suggestion for the developer:
>>> If the min value is equal to the maximum value of a (magnitude of a) vector
>>> and min value > 0 --> something should be displayed.
>>> 
>>> 
>>> Matthias Lang
>>> 
>>> _______________________________________________
>>> gmsh mailing list
>>> gmsh at geuz.org
>>> http://www.geuz.org/mailman/listinfo/gmsh
>> 
> <js.pos>

-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science 
http://www.montefiore.ulg.ac.be/~geuzaine