Hi Jacques,
currently i use tau2plt, then generate "EnsightGold" output and read
that in. Would be very nice if you can share your NetCDF-Reader for
paraview...
You working at ARA in Bedford? I was there last December for a
Solar-Training - there i had my first contact with paraview - it is a
really nice tool - thats why i am now working with it more and more
Best regards,
Stefan
Hi Stefan,
Are you using ParaView to load in Tau datasets ?
I have been using it, for that purpose, and have written a Tau data
loader for ParaView.
I find it very useful.
Regards,
Jacques
Aircraft Research Association
2009/1/8 Stefan Melber <[email protected]
<mailto:[email protected]>>
Hi Ken,
I took a look at this. To answer the first question, compute
derivatives and gradient (unstructured) are fairly similar.
The compute derivatives filter takes point scalars and
computes the gradient in the centroid of each cell (thus
producing cell data). This is a fairly straightforward
operation as the vtkCell classes can compute the gradient
anywhere in the cell from point data.
The gradient filter can take point data and find the data at
the points or take cell data and find (an estimate of) the
gradient at the cell centroids. The algorithm for finding the
cell-centered is similar to that in compute derivatives and
should take about the same amount of time. The algorithm for
finding point-centered data is to find the gradient at each
point of each cell and average the results at each point.
On your prompting, I can the gradient filter through a
performance monitor and realized that it was spending about
half its time checking for degenerate cells. I just checked
in a change that makes the check much faster. However,
because the gradient filter is doing more derivative
calculations, it will always be slower than compute derivatives.
So its possible to change the gradient-filter to get a speedup? -
nice. Please let me know when this change is checked in into the
cvs-version of paraview - i will check it here again.
The last statement i dont understand: using the "compute
derivatives" i get overall a tensor with 9 derivatives, using the
"gradient" filter i get only three. So in my case, because i need
the complete tensor (to compute the strain-rate of the flow) i
have to call three times the "gradient"-filter. So overall, in
both cases 9 derivatives are calculated - or am i wrong?
That said, I think it should be fairly easy to add a mode that
approximates point gradients by computing cell gradients using
the point data and then doint a point-to-cell conversion much
like you were doing. Would anyone want that?
I have done it by combining both steps in a custom filter ... so
thats enough for me. If other users need it - why not.
Yust a small remark regarding paraview overall: its really a nice
tool! I currently do much comparison work between paraview,
fieldview and ensight. We have all packages here at DLR (the
german aerospace center) and i want to find out if all features we
need from fv and ensight can be done although in pv ... it seems,
thats the case. And pv is much more flexible then the other
packages. Further on, the speed is critical, because we have huge
unstructured datasets (typical: > 20e6 points up to 50e6,
sometimes time dependend). So the complete parallel setup of pv
can be a great help here - with (serial) fv for example we run all
the time on the limits of our workstations (16 GB main memory, 4
cores) ...
Best regards,
Stefan
-Ken
On 1/7/09 2:44 AM, "Stefan Melber" <[email protected]> wrote:
Hi,
i have a question regarding the filters "Compute
Derivatives" and
"Gradient (Unstructured)". I have to calculate a equation on an
unstructured data set with some derivatives of the velocity.
Using the "Gradient (Unstructured)" it works, but it is
really slow.
Using the "Compute Derivatives" and the convert the result
back from
cell centers to points i can get nearly the same results -
but much
faster (the most time takes the conversion from cell center to
points!).
So i made a comparison of both results with an isosurface
of the
magnitude of the difference between both gradients an i can
only find
minor changes. So my question to the developers: Where is the
difference
between both filters? Why is the "Gradient (Unstructured)"
so much
slower?
Best regards and thank you in advance,
Stefan
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