[Gmsh] Time-Dependent Cuts

[Christophe Geuzaine]

Radek Pecher wrote:
> 
> Dear Gmsh authors,
> 
> First of all, I would like to thank you for making Gmsh publicly
> available - it truly is an excellent free software!
> 
> 1. My main question to you stems from my need for visualising
> time-dependent fields at various cut-planes through the domain of
> interest. If I am using the default plugins correctly, it appears that
> the cut-plugins presently do not process time-dependent fields, as
> opposed to the skin-plugin which does. Here is my example code:

Yes, it's a limitation due to the implementation of the cut as a
particular case of a levelset. I'll change this.

> 2. My second, less important question, is the following: Is it just my
> Cygwin-based installation or you cannot see the cell-centred arrow
> either?
> 
> // ----------------------------------------------
> View "test"
> {
>   VT(-1.38142, 0.680203, -0.969318, 0.694375, 1.79726, -0.255058,
> 1.86376, 0.341392, 0.560109)
>     {0.404305, -0.177619, -0.897212, 0.404305, -0.177619, -0.897212,
> 0.404305, -0.177619, -0.897212};
> };
> // ----------------------------------------------
> 
> If I visualise this vector triangle, it properly shows three arrows at
> the vertices, however no arrow whatsoever in the centre of the
> triangle... (My options are not too different from the default ones.)
> Any ideas?

This is caused by the roundoff error introduced when computing the mean
value at the barycenter of the element. The display range (min/max) is
computed from the nodal values, whereas the drawing test is done on the
mean value. In your single triangle test all nodal values are equal, and
thus min = max exactly. The mean value computed at the barycenter is
slightly (1.e-15) outside the range... I'll add a small tolerance in the
test.

Christophe

-- 
Christophe Geuzaine

Tel: (626) 395-4552    http://www.geuz.org
Fax: (626) 578-0124    mailto:geuzaine at acm.caltech.edu