[Paraview-developers] Is it possible to implement a POD filter in paraview using python?

Fri Apr 24 08:19:27 EDT 2015

Hi, Andy Bauer

Thanks for your reply. I just read the blogs and it seems it is possible to use “Programmable Filter” to access data of different timesteps by writing a “RequestUpdateExtentScript” like this:

#----------------------------------------------

RUEScript = '''

info0 = inInfo[0].GetInformationObject(0) # Ask for the next timestep.

info0.Set(vtk.vtkStreamingDemandDrivenPipeline.UPDATE_TIME_STEP(),

{})

info1 = inInfo[1].GetInformationObject(0) # Ask for the next timestep.

info1.Set(vtk.vtkStreamingDemandDrivenPipeline.UPDATE_TIME_STEP(),

{})

return 1

'''

pf.RequestUpdateExtentScript = RUEScript.format(t1,t2) 

#----------------------------------------------

However, I get this error msg on my workstation:

NameError: global name 'inInfo' is not defined

I am using paraview 4.3.1, and the workstation is running on Ubuntu 12.04. I tested the code above in paraview 4.3.1 on windows 8.1 and it still does not works.

And I checked the parameters of “RequestUpdateExtentScript” by:

#----------------------------------------------

print dir()

print locals()

#----------------------------------------------

The result shows that there is no inInfo, but there are “request”, “inputs”, “output”, just like The “Script” of “Programmable filter”. Then I realize that this “Programmable filter” is a proxy to the VTK’s “Programmable filter”. And I cannot access the InformationObject behind the proxy. But I do not know much about the python interface of Proxies.

Now my question is: how can I access vtk Objects directly? Should I use vtk instead of paraview to accomplish my goal?

Di Cheng

From: Andy Bauer [mailto:andy.bauer at kitware.com] 
Sent: Thursday, April 23, 2015 9:26 PM
To: Di Cheng
Cc: paraview-developers at paraview.org
Subject: Re: [Paraview-developers] Is it possible to implement a POD filter in paraview using python?

The best way would be to implement this in C++ but it's also doable in Python. 

If you want to do it in Python I'd suggest reading through Berk Geveci's blog posts on Python and VTK (http://www.kitware.com/blog/home/user/53). The one most relevant is probably http://www.kitware.com/blog/home/post/783 but the others give good background. 

Regards,

Andy

On Thu, Apr 23, 2015 at 3:55 AM, Di Cheng <chengdi at imech.ac.cn <mailto:chengdi at imech.ac.cn> > wrote:

Hi, everyone.

I am interested in using proper orthogonal decomposition to analyze unsteady flow field data obtained from CFD in paraview. I tried to implement it using python. But I am not sure if there is a better way to implement the POD algorithm described in chapter 3.2 of <http://web.mit.edu/kwillcox/Public/Web/BTTanMS.pdf> http://web.mit.edu/kwillcox/Public/Web/BTTanMS.pdf 

The algorithm can be summarized as: 
0. get timestepvalues of interest as t_i, i=1..N 
1. load field P of two timesteps such as as P_i=P(t_i),P_j=P(t_j) 
2. calculate the correlation R_ij = inner_product(P_i,P_j)/N, the definition of inner product could be integration of P_i*P_j over the volume. 
3. get the eigen values lambda_i and corresponding right egien vector eV_ii of matrix {R_ij} 
4. construct the i-th POD basis psi_i = sum(dot(eV_ij,P_j),j=1..N), usually, only the first m bases are used. 
5. reconstruct Pr_m field using first m POD bases: 
Pr_m = sum(lambda_i * psi_i, i = 1.. m)

6.output the lambda_i, psi_i and Pr_m

The algorithm is simple but the problem is to avoid loading the very large 3D dataset of all timesteps into memory. I tried to use “c1.UpdatePipeline(t_1); c2.UpdatePipeline(t_2);”  to load two timesteps at one time to avoid this problem. I do not know if this method works.

Then I tried to implement the following algorithm using python. A pipeline is used to calculate the inner product via Programmable Filter and Integrate Variables. And I can get the correlation matrix and eigen values and eigen vectors. 

The final step is the most difficult part in python. I do not know how to implement it in python. I did not implement it yet. I do not want to use Fetch method to collect all data to the master node. But the functionality of python shell seems limited and accessing the cells’ structure is difficult. I want to know how TemporalAverge filter works but I cannot identify where it is in the source code. (I am not familiar with software development using C++).

So, could anyone help me to finish it or tell me it is not possible?

Thanks

p.s. I just posted a Request a New Feature in http://paraview.uservoice.com/forums/11350-general/suggestions/7671768-proper-orthogonal-decomposition-analysis-filter

Di CHENG (Ph.D. candidate)

Supersonic Combustion Group

State Key Laboratory of High Temperature Gas Dynamics

Institute of Mechanics, Chinese Academy of Sciences
ADDRESS: No.15 Beisihuanxi Road, Beijing (100190)
P. R. China
E-mail:  <mailto:chengdi at imech.ac.cn> chengdi at imech.ac.cn

Phone:  <tel:%2B86-10-82544053> +86-10-82544053

Fax:  <tel:%2B86-10-82544034> +86-10-82544034

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