[Paraview] Gauss points

Wed Dec 4 13:50:21 EST 2013

Hi Marios,

>          If I apply the InterpolatetoQuadraturePoints filter as shown 
> in Figure 2 the output result is
> basically empty. 
If you write the data arrays containing the scalar values at the Gauss 
points to the file then you do not want to apply the "interpolate to qp" 
filter. This filter's purpose is to generate these array from nodal 
values. This means that you have to have the nodal values. You mentioned 
that you've removed them so that you won't get confused, and that will 
prevent this filter from working.

> If I apply the GenerateQuadraturePoints filter as shown in Figure 3 
> the field data
> transformed to point data. Hence after the application of the 
> GenerateQuadraturePoints the previous 9
> point data and 4 cell data are not exist anymore but together with the 
> field data they transformed to 16
> point data representing the 16 Gauss points. Those 16 points have the 
> correct coordinates and T values.
yes, that's what should happen. You're visualizing a different geometry 
- the Gguass points - so data arrays on the original geometry will not 
be available.

>          I tried to reproduce the same example using the GID software 
> and the results are shown in
> Figure 4. Can I do something similar with Paraview? I want to have 
> these contour lines instead of just
> point's information. I want to continue use Paraview because has some 
> really powerful features that I
> like and I am sure this is trivial but I cannot find some way to do it.
you can't generate the contours on a point set, you first need to mesh 
it. One way to do this would be to apply "delaunay 2d" to the point set. 
Other approaches would be more efficient and produce better results but 
would require you to write some code. eg. write out the mesh on the 
Gauss points directly from your simulation.

On 12/04/2013 10:30 AM, Marios Mavros wrote:
> Hi Burlen,
>
> Thank you for your help and for your example that you have provided. I 
> followed your instructions and I prepare a small pdf explaining what I 
> did and what I expected as a final result. I thought that this 
> procedure was the solution to my problem but maybe I have to do 
> something extra or something different. Attached you will find also 
> the file that I used.
>
> Thank you again for your help
>
> Marios
>
>
> On Tue, Dec 3, 2013 at 2:46 AM, Burlen Loring <bloring at lbl.gov 
> <mailto:bloring at lbl.gov>> wrote:
>
>
>>     1. What the numbers 0 4 8 12 (line 24) represent?
>     This is the offset array used by VTK for random access into data
>     on the quadrature points data. To generate it you go cell by cell
>     and accumulate the number of quadrature points used by each cell.
>     The next cell's data offset is the sum of the previous cell's
>     number of quadrature points.
>
>     note that the documentation says that each array has a quadrature
>     scheme dictionary, but this changed. the dictionaries are stored
>     in the offeset array. we did this so that you only need to define
>     one quadrature scheme dictionary for many arrays.
>
>
>>     2. What the QuadratureWeights are all zero (line 37)?
>     Those aren't currently used in VTK but we have a place holder for
>     them in case they are needed in user developed custom filters or
>     later in VTK.
>
>
>>     3. In your example there are 4 cells with 4 Gauss points in each
>>     cell. In total 16 Gauss points. If I want to assign to each Gauss
>>     point one value of stress or strain how I have to write those 16
>>     values in xml format.
>     in my example you would read this file into PV and apply
>     "interpolate to quadrature points" and then "generate quadrature
>     points".
>
>     You're asking about writing the data on the Gauss points into the
>     file. You have to store them in VTK FieldData and add an
>     information key to each array that names the offset array. You
>     have to order them correctly according to the offsets array and
>     quadrature scheme. for example the pdf I sent before shows how
>     each cell's quadrature points are ordered for one scheme. you
>     won't write the points themselves, just the data values.
>
>     the T FieldData array in the following file is an example of
>     containing scalar values at quadrature points (watch out there's
>     also a PointData array named T that stores the nodal values),
>     http://www.hpcvis.com/vis/images/vtk-quadrature-points-example/quadrature-points-example-2.vtu
>
>     after reading such a file into PV, you could see the arrays in the
>     spreadsheet view but to see them in the 2d/3d view you'll need to
>     apply the "generate quadrature points" filter to produce the point
>     set and transfer the data onto it.
>
>
>     On 12/01/2013 10:26 PM, Marios Mavros wrote:
>>     Hi Burlen,
>>
>>     Your example was really helpful to understand many thing about
>>     the xml format and I want to thank you about that, but I still
>>     have some questions.
>>
>>     1. What the numbers 0 4 8 12 (line 24) represent?
>>     2. What the QuadratureWeights are all zero (line 37)?
>>     3. In your example there are 4 cells with 4 Gauss points in each
>>     cell. In total 16 Gauss points. If I want to assign to each Gauss
>>     point one value of stress or strain how I have to write those 16
>>     values in xml format. Can you please sent me an example with this
>>     information?
>>
>>     Thank you very much
>>
>>     Marios
>>
>>
>>     On Sat, Nov 30, 2013 at 4:28 PM, Burlen Loring <bloring at lbl.gov
>>     <mailto:bloring at lbl.gov>> wrote:
>>
>>         Hi Mario,
>>
>>         sending again to the list. the weights have 2 dimensions i
>>         (node id) and j (Gauss point id), so to generate
>>         ShapeFunctionWeights for a new QuadratureSchemeDefinition 
>>         what you do is evaluate each shape function at each Gauss
>>         point. For the linear quadrilateral you'll end up with 16
>>         weights. For example see the example
>>
>>         http://www.hpcvis.com/vis/images/vtk-quadrature-points-example/vtk-quadrature-points-example.pdf
>>         http://www.hpcvis.com/vis/images/vtk-quadrature-points-example/quadrature-points-example.vtu
>>
>>         Burlen
>>
>>
>>         On 11/29/2013 3:34 PM, Marios Mavros wrote:
>>>         Hi Burlen,
>>>
>>>         I want to thank you for the information that you send me. I
>>>         read the paper and I try to made a simple example in xml
>>>         format for a 4 node quadrilateral element but it didn't work
>>>         for me. Attached you will find the element formulation that
>>>         I used with the shape functions and a .vtu file with my
>>>         example. If I want to give 4 stress values in the 4 Gauss
>>>         points ( lets say 0.1 0.2 0.4 -0.1) can you please write in
>>>         the .vtu file the missing information in order to understand
>>>         haw I have to write a correct file in xml format.
>>>
>>>         Thank you very much
>>>
>>>         Marios Mavros
>>>
>>>
>>>         On Wed, Nov 27, 2013 at 2:56 PM, Burlen Loring
>>>         <bloring at lbl.gov <mailto:bloring at lbl.gov>> wrote:
>>>
>>>             You'll need to use an XML file format. There's some
>>>             documentation in the following link. It's slightly dated
>>>             but should get you started.
>>>             http://www.vtk.org/Wiki/images/7/78/VTK-Quadrature-Point-Design-Doc.pdf
>>>             The ctest,
>>>             VTK/Filters/General/Testing/Cxx/TestQuadraturePoints.cxx, could
>>>             be used as an example.
>>>
>>>
>>>             On 11/27/2013 02:32 PM, Marios Mavros wrote:
>>>>             Hi
>>>>
>>>>             I have wrote a simple program in Fortran that transform
>>>>             the output of a finite element software in vtk Legacy
>>>>             Format. I don't know how to handle the Gauss points
>>>>             values. For example in my case my cells have 4 Gauss
>>>>             points and I have 4 values (for example strain in
>>>>             x-direction) for each cell. How I have to write the vtk
>>>>             file taking into account that each cell has many Gauss
>>>>             points?
>>>>
>>>>             Thank you
>>>>
>>>>             Marios
>>>>
>>>>
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>>>
>>>
>>
>>
>
>

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