[Paraview] unstructured grid, programmable filters: extract, process array data

Wed Feb 16 14:56:30 EST 2011

From:
http://paraview.org/Wiki/ParaView/Users_Guide/Python_Programmable_Filter#Mixing_VTK_and_NumPy_APIs

The secret to conversion is in paraview.vtk.dataset_adapter.

David E DeMarle
Kitware, Inc.
R&D Engineer
28 Corporate Drive
Clifton Park, NY 12065-8662
Phone: 518-371-3971 x109

On Wed, Feb 16, 2011 at 2:41 PM, Tim Gallagher <tim.gallagher at gatech.edu> wrote:
> To access the components of the vector, you have to first pass it through a regular Calculator filter where the result is just the component you want. So you would need to go through two regular Calculator filters, one to extract each component.
>
> As for accessing more functions, I guess you're out of luck on that (for now). Back to the programmable filter I suppose.
>
> There is a function, I can't remember the name, to convert a vtkDataArray into a numpy array -- that's what you will want to use inside your prog. filter. You can then do any python thing on it and then convert it back into a data array. I can't remember the name of it though, perhaps somebody else can help you there if you can't find it online.
>
> Tim
>
> ----- Original Message -----
> From: "Nico Schlömer" <nico.schloemer at gmail.com>
> To: "Andy Bauer" <andy.bauer at kitware.com>
> Cc: gtg085x at mail.gatech.edu, "tim gallagher" <tim.gallagher at gatech.edu>, paraview at paraview.org
> Sent: Wednesday, February 16, 2011 12:49:28 PM
> Subject: Re: [Paraview] unstructured grid, programmable filters: extract, process array data
>
>> the math.atan2 function (it's not listed in the web page of python
>> calculator functions)
>
> So the Python Calculator only allows for the functions listed on the
> webpage? That'd be quite limiting, really.
>
> The expression
>
>   dot( psi_, psi_ )
>
> works, for example (and 'dot' is listed, too).
> Well well. What would be needed then is access to the individual
> components of each of the 2-component vectors in psi_, as well as
> access to a wider range of Python functions.
>
> --Nico
>
>
>
>
> On Wed, Feb 16, 2011 at 5:39 PM, Andy Bauer <andy.bauer at kitware.com> wrote:
>> Hmm, I tried extracting out the components using the Calculator filter and
>> then using the PythonCalculator filter to do that math.atan2 function.
>> Underneath the covers I believe there is a conversion from a vtkDataArray to
>> a numpy array and then back again.  I don't think this is getting done for
>> the math.atan2 function (it's not listed in the web page of python
>> calculator functions) so you may be stuck here unless someone else has an
>> idea.
>>
>> Andy
>>
>> On Wed, Feb 16, 2011 at 10:25 AM, Nico Schlömer <nico.schloemer at gmail.com>
>> wrote:
>>>
>>> That sounds *exactly* like what I need. Great!
>>> I'm having problems selecting the data sets though: Where
>>> "atan(psi__Y/psi__X)" works with the calculator filter, "math.atan2(
>>> psi__Y, psi__X)" fails in the PythonCalculator with
>>>
>>> ============== *snip* ==============
>>> Traceback (most recent call last):
>>>  File "<string>", line 19, in <module>
>>>  File "<string>", line 27, in RequestData
>>> NameError: name 'psi__Y' is not defined
>>> ============== *snap* ==============
>>>
>>> I looked at http://www.paraview.org/Wiki/Python_Calculator but
>>> couldn't figure out what's wrong.
>>>
>>> --Nico
>>>
>>>
>>>
>>> On Wed, Feb 16, 2011 at 2:43 PM, Tim Gallagher <tim.gallagher at gatech.edu>
>>> wrote:
>>> > You can use the Python Calculator, which will let you use any valid
>>> > Python expression -- such as math.atan2().
>>> >
>>> > Tim
>>> >
>>> > ----- Original Message -----
>>> > From: "Nico Schlömer" <nico.schloemer at gmail.com>
>>> > To: "Andy Bauer" <andy.bauer at kitware.com>
>>> > Cc: paraview at paraview.org
>>> > Sent: Wednesday, February 16, 2011 8:29:02 AM
>>> > Subject: Re: [Paraview] unstructured grid, programmable filters:
>>> > extract, process array data
>>> >
>>> > Almost there!
>>> >
>>> >> atan(coordsX/coordsY)
>>> >
>>> > If instead of coordsX I use psi__{X,Y}, things work. However, I need
>>> > something slightly different than atan: I'd like to get the complex
>>> > argument of a complex number X+iY (i.e., the angle with the positive
>>> > real axis). It's quite ~similar~ to what atan does, see for example
>>> > <http://gcc.gnu.org/onlinedocs/gcc-4.0.4/gfortran/ATAN2.html>. In
>>> > Python, the function is called math.atan2() as well.
>>> > ParaView's  calculator filter does however not support atan2(), and
>>> > that was my original motivation to look at programmable filters
>>> > actually. Well, it'd be much nicer if the same thing could be done
>>> > with the calculator of course!
>>> > Workarounds?
>>> >
>>> > --Nico
>>> >
>>> >
>>> >
>>> >
>>> >
>>> > On Tue, Feb 15, 2011 at 6:56 PM, Andy Bauer <andy.bauer at kitware.com>
>>> > wrote:
>>> >> This sounds like a job for the calculator filter.
>>> >> "coordsX^2+coordsY^2" for
>>> >> your first example (or "psi__X^2+psi__Y^2" for the psi variables) and
>>> >> "atan(coordsX/coordsY)" for the second example.
>>> >>
>>> >> It can operate on point or cell data (set in the Attribute Model
>>> >> drop-down
>>> >> menu), replace invalid numbers with a specified value, and you can name
>>> >> the
>>> >> resulting array as well.
>>> >>
>>> >> Andy
>>> >>
>>> >> 2011/2/15 Nico Schlömer <nico.schloemer at gmail.com>
>>> >>>
>>> >>> Hi all,
>>> >>>
>>> >>> I've been looking at
>>> >>> <http://www.paraview.org/Wiki/Python_Programmable_Filter> to create a
>>> >>> programmable filter, but I'm a bit lost as to whether or not I need
>>> >>> GetPolyData, CopyAttributes,...
>>> >>>
>>> >>> Essentially, I have an unstructured grid in an ExodusII file (like the
>>> >>> attached file actually) with point data "psi" in it that has two
>>> >>> components (X,Y). I can plot psi:X, psi:Y, and psi:magnitude alright
>>> >>> with the default GUI options, but what I would really like to have
>>> >>> plotted is X^2+Y^2 (no sqrt()) and something along the lines of
>>> >>> arctan(Y/X).
>>> >>>
>>> >>> Is there simple code somewhere some that takes array data off of an
>>> >>> unstructured grid, does something with it and returns the extra array
>>> >>> from the filter?
>>> >>>
>>> >>> Cheers,
>>> >>> Nico
>>> >>>
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>>> >>
>>> >>
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>>> _______________________________________________
>>> Powered by www.kitware.com
>>>
>>> Visit other Kitware open-source projects at
>>> http://www.kitware.com/opensource/opensource.html
>>>
>>> Please keep messages on-topic and check the ParaView Wiki at:
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>>
>>
> _______________________________________________
> Powered by www.kitware.com
>
> Visit other Kitware open-source projects at http://www.kitware.com/opensource/opensource.html
>
> Please keep messages on-topic and check the ParaView Wiki at: http://paraview.org/Wiki/ParaView
>
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