[Paraview] *****SPAM***** *****SPAM***** Re: Questions regarding: volume calculation, xyplot along a curve and tensor calculation

[Zhanping Liu]

I will check it.

Thanks.

-Zhanping

On Sat, Apr 11, 2009 at 12:15 AM, Takuya OSHIMA
<oshima at eng.niigata-u.ac.jp>wrote:

> Hi Jie, Renato,
>
> There had been a bug until ParaView 3.4 that led the volume of a wedge
> to have been miscalculated as a negated volume of a tetrahedron.
> http://www.paraview.org/pipermail/paraview/2008-August/009246.html
> http://paraview.org/Bug/view.php?id=7588
>
> The bug has been fixed with the recent CVS versions.
>
> I can confirm that the bug also affects volume calculations of clipped
> hexahedral meshes as well by Jie's test.vtk. If I try the .vtk with a
> CVS version and follow Jie's procedure I get a volume of 4.95177e-13
> which is closer to the analytic value of 5.23599e-13. However if I
> revert the bugfix (revert vtkWedge.cxx from the current revision 1.7
> to ParaView 3.4's 1.5) I get the identical value with what Jie got,
> 3.32862e-13.
>
> Takuya OSHIMA, Ph.D.
> Faculty of Engineering, Niigata University
> 8050 Ikarashi-Ninocho, Nishi-ku, Niigata, 950-2181, JAPAN
>
>
> From: Renato Elias <rnelias at gmail.com>
> Subject: Re: [Paraview] Questions regarding: volume calculation, xyplot
> along a curve and tensor calculation
> Date: Fri, 10 Apr 2009 22:39:36 -0300
>
> > It seems rounding errors... try to scale your model at least 100x to see
> > what happens...
> >
> > Just to reforce Jie Xu's problem. It's not the first time the Integrate
> > Variable presents issues in volume calculations. Take a look:
> >
> http://markmail.org/message/67dkxpypfodylfnr#query:volume%20integration%20paraview%20renato+page:1+mid:67dkxpypfodylfnr+state:results
> >
> > In my case, I don't remember if the problem was solved....
> >
> > I tried to find my dataset to test it again but I haven't found (yet)....
> > :-(
> >
> > Renato.
> >
> >
> >
> > On Fri, Apr 10, 2009 at 4:30 PM, Jie Xu <victoryxj at gmail.com> wrote:
> >
> >> Hi Berk,
> >>
> >> Thanks for looking at my questions.
> >>
> >> 1) I attached a sample data set: test.vtk, and the screenshot of my
> >> paraview window, from which you can see that the clip is created at
> >> (0,0,0) with radius of 50e-6, and the calculated volume is
> >> 3.32862e-13, which is much less than what it should be.
> >> (Interestingly, in this specific case, the calculated volume is about
> >> 2/pi times the real volume.)
> >>
> >> 2) Thanks for letting me know.
> >>
> >> 3) Unfortunately, I have no experience with Python. Now I am trying to
> >> see if I can use matlab to do the tensor calculates and modify the vtk
> >> file readable by paraview.
> >>
> >> Regards,
> >> Jie
> >>
> >> On Thu, Apr 9, 2009 at 1:51 PM, Berk Geveci <berk.geveci at kitware.com>
> >> wrote:
> >> > Hi Jie,
> >> >
> >> >> 1) Volume calculation:
> >> >> I found that the "integrate variables" over a sphere clip never gives
> >> >> the correct volume. For example, I tried to use a very simple
> geometry
> >> >> and a very fine mesh (a 200x200x200 micron cube with 2 micron cube
> >> >> elements), and use paraview to generate a sphere clip that has radius
> >> >> of 50 micron in the center of that cube, then I apply the "integrate
> >> >> variables" filter to the clip and show the "Cell Data", it gives a
> >> >> volume of 4.78818e-13 instead of 5.236e-13, which is 4/3*pi*r^3. The
> >> >> discrepancy is so large that it just cannot be due to the coarseness
> >> >> of the mesh. Different mesh and different size of clips gives
> >> >> different discrepancies, and I cannot find any obvious relationship
> >> >> between the paraview-calculated volume and the real volume.
> >> >
> >> > When I create a 100^3 wavelet and clip it with a sphere of radius 20,
> >> > I am getting a volume of 33447.5 which is pretty close to the analytic
> >> > value of 33510.3. Can you send me a dataset that demonstrates this
> >> > problem?
> >> >
> >> >> 2) X-Y plot: how can I do a xyplot of a scalar along a curved line?
> >> >> For example, if I have the pressure field data from a
> >> >> flow-around-a-cylinder case, I want to plot the pressure along the
> >> >> surface of the cylinder as a function of angle or arc length.
> >> >
> >> > You can't, yet. I am working on that feature for the next release.
> >> >
> >> >> 3) tensor calculation: I have the pressure field and velocity field
> >> >> calculated from a CFD tool (Transat in my case), how do I calculate
> >> >> stress tensors at each point from P V field in paraview?
> >> >
> >> > Let me ask a question back : do you have any Python knowledge? We are
> >> > working on making this really simple but currently the array
> >> > calculator is too limited and cannot produce tensors. However, this is
> >> > doable using the programmable filter.
> >> >
> >> > -berk
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-- 
Zhanping Liu, PhD
Kitware, Inc.
28 Corporate Drive
Clifton Park, NY 12065-8662
Phone: 518-371-3971 x 138
http://www.zhanpingliu.org
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