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 <[email protected]
<mailto:[email protected]>> 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 <[email protected]
<mailto:[email protected]>> 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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