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

Tim Gallagher tim.gallagher at gatech.edu
Wed Feb 16 14:41:20 EST 2011 

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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>>
>> Visit other Kitware open-source projects at
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>> Please keep messages on-topic and check the ParaView Wiki at:
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