[Paraview-developers] Filter with multiple time-aware outputs

[Ellon Paiva]

     Utkarsh,

On 05/27/2016 02:42 PM, Utkarsh Ayachit wrote:
>> Is it possible to trigger a file reader from a filter input? If it's
>> possible I think I can achieve this using two filters in sequence in the
>> pipeline: the first dump data on files, and the second would read the data
>> from the disk when it receives a new data on its input port. This way the
>> second filter would know already the number of time steps in its
>> RequestInformation() to configure the output ports before reading the files.
> I am not sure I follow, but what I followed doesn't seem like it would
> work. The second filter still only receive new data on its input in
> RequestData() so not sure how it will already know the timesteps.

Well, if I know the path to the files I'm writing in the first filter 
(for example: /tmp/myfiles_1.vtk, /tmp/myfiles_2.vtk, etc) I could just 
check how many of these files exist in the disk, and this number would 
be the number of time steps. The value of the timesteps is just the 
index of the file (1, 2, etc).

> Do you want to try explaining what are you trying to do succinctly,
> maybe someone can suggest an alternative approach.

OK, let me explain. I'm using a library that performs ICP 
(libpointmatcher) on point clouds. The library itself is very modular on 
it's components (data filters, error minimizers, matchers, outlier 
rejectors, etc), it's structured in a pipeline fashion, like in 
ParaView. It has already an option to inspect the ICP process by dumping 
the point clouds (i.e. the reference cloud and the one being matched) 
and the point associations between these clouds in .vtk files (three 
files for every iteration of the ICP loop). These files can be loaded on 
ParaView through a standard reader and it's possible to inspect the ICP 
process through animation.

What I want to implement is a way to reconfigure the parameters of the 
libpointmatcher's ICP pipeline through ParaView, in a way that if a 
parameter is changed in any libpointmatcher module in paraview (through 
filter properties), one can just press "Apply" to trigger the ICP run 
and the result would be exhibited in ParaView. I believe this would 
improve the workflow of configuring ICP solutions using this library.

The data filters classes are already wrapped, and I want to wrap the 
"ICP core". As an iteractive process, it has a loop, and currently I 
don't know how to implement loops in paraview's pipeline (I know there's 
something to do with a vtkExecutive) and also the pipeline would be 
somehow complex for the user to build. So I decided to create a single 
filter that wraps all the loop part of the ICP pipeline.

But then you told me I cannot configure dynamically the number of 
outputs of a filter from inside it's RequestData(), and I don't know how 
many iteractions of ICP I'll need before converging (if converging). One 
information I have is the maximum number of iteractions I may have, but 
the algorithm may finish before it.

I'm attaching a image of the pipeline I was implementing here. This may 
help you to understand.

Sorry for the long email.

Regards,

Ellon

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