Fwd: apply filter multiple times

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---------- Forwarded message ---------
De: Paulo Carvalho <[email protected]>
Date: dom, 7 de jul de 2019 =C3=A0s 10:06
Subject: Re: [vtkusers] apply filter multiple times
To: Martin Genet <[email protected]>


Hi, Martin!

       If I understood right, you want to create a
vtkUnstructuredGridAlgorithm specialization so you can plug it in to a VTK
pipeline.  That would be "easy" if it were in C++, but it seems you want to
do it in pure Python.  Thus, your problem is two-fold:

   1) You need to learn know how to extend C++ classes in Python and make
your Python class usable in a C++ framework:
https://stackoverflow.com/questions/2200912/inheritance-in-python-c-extensi=
on
.

   2) You need to implement a custom sub-class of
vtkUnstructuredGridAlgorithm in Python to be able to plug it in to some VTK
pipeline.

     I've never tried it myself, but be ready for some real headaches as I
recall the pain that was to write CORBA wrappers for Java-C++
interoperabilty.

     I think you'd be better off if you write your custom
vtkUnstructuredGridAlgorithm subclass in C++ and use it in Python like
other VTK classes.  Overriding vtkUnstructuredGridAlgorithm alone will be
enough trouble.

all the best,

Paulo

Em s=C3=A1b, 6 de jul de 2019 =C3=A0s 17:31, Martin Genet <
[email protected]> escreveu:

> Dear all:
>
> I am having some issue setting up a rather complex pipeline involving,
> but not exclusively, vtk objects and filters. I think basically the
> issue boils down to this: I create an unstructured grid with some vector
> field, warp it, modify the vector field (outside vtk), warp it again,
> etc. Pretty basic, right? Of course I do not want to reallocate an
> unstructured grid for the warped mesh each time I run the warp filter,
> but rather modify the one that is allocated the first time I run the
> warp filter. Makes sense? I have done this many times, for pipelines
> that only involve vtk stuff. However, I am not sure how to do this for
> pipelines involving non-vtk operations. Attached is a minimal example: I
> create a sphere, warp it along the normals, scale the normals, warp it
> again using the already existing warp filter (here the scaling is not
> taken into account for some reason), and warp it using a new warp filter
> (here it is, but I guess it creates a new object instead of modifying
> the existing one, right?). This seem like a trivial issue, but I cannot
> seem to figure it out. Can someone help me? Thank you so much.
>
> Martin
> _______________________________________________
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<div dir=3D"ltr"><br><br><div class=3D"gmail_quote"><div dir=3D"ltr" class=
=3D"gmail_attr">---------- Forwarded message ---------<br>De: <b class=3D"g=
mail_sendername" dir=3D"auto">Paulo Carvalho</b> <span dir=3D"auto">&lt;<a =
href=3D"mailto:[email protected]">[email protected]</=
a>&gt;</span><br>Date: dom, 7 de jul de 2019 =C3=A0s 10:06<br>Subject: Re: =
[vtkusers] apply filter multiple times<br>To: Martin Genet &lt;<a href=3D"m=
ailto:[email protected]">[email protected]</a>&gt=
;<br></div><br><br><div dir=3D"ltr"><div dir=3D"ltr"><div dir=3D"ltr"><div>=
<div>Hi, Martin!<br><br></div>=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 If I und=
erstood right, you want to create a vtkUnstructuredGridAlgorithm specializa=
tion so you can plug it in to a VTK pipeline.=C2=A0 That would be &quot;eas=
y&quot; if it were in C++, but it seems you want to do it in pure Python.=
=C2=A0 Thus, your problem is two-fold:<br><br></div>=C2=A0=C2=A0 1) You nee=
d to learn know how to extend C++ classes in Python and make your Python cl=
ass usable in a C++ framework: <a href=3D"https://stackoverflow.com/questio=
ns/2200912/inheritance-in-python-c-extension" target=3D"_blank">https://sta=
ckoverflow.com/questions/2200912/inheritance-in-python-c-extension</a>.<br>=
<br></div><div>=C2=A0=C2=A0 2) You need to implement a custom sub-class of =
vtkUnstructuredGridAlgorithm in Python to be able to plug it in to some VTK=
 pipeline.<br><br></div><div>=C2=A0=C2=A0=C2=A0=C2=A0 I&#39;ve never tried =
it myself, but be ready for some real headaches as I recall the pain that w=
as to write CORBA wrappers for Java-C++ interoperabilty.<br><br></div><div>=
=C2=A0=C2=A0=C2=A0=C2=A0 I think you&#39;d be better off if you write your =
custom vtkUnstructuredGridAlgorithm subclass in C++ and use it in Python li=
ke other VTK classes.=C2=A0 Overriding vtkUnstructuredGridAlgorithm alone w=
ill be enough trouble.<br><br></div><div>all the best,<br><br></div><div>Pa=
ulo<br></div></div></div><br><div class=3D"gmail_quote"><div dir=3D"ltr" cl=
ass=3D"gmail_attr">Em s=C3=A1b, 6 de jul de 2019 =C3=A0s 17:31, Martin Gene=
t &lt;<a href=3D"mailto:[email protected]" target=3D"_blank">m=
[email protected]</a>&gt; escreveu:<br></div><blockquote class=
=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rg=
b(204,204,204);padding-left:1ex">Dear all:<br>
<br>
I am having some issue setting up a rather complex pipeline involving, <br>
but not exclusively, vtk objects and filters. I think basically the <br>
issue boils down to this: I create an unstructured grid with some vector <b=
r>
field, warp it, modify the vector field (outside vtk), warp it again, <br>
etc. Pretty basic, right? Of course I do not want to reallocate an <br>
unstructured grid for the warped mesh each time I run the warp filter, <br>
but rather modify the one that is allocated the first time I run the <br>
warp filter. Makes sense? I have done this many times, for pipelines <br>
that only involve vtk stuff. However, I am not sure how to do this for <br>
pipelines involving non-vtk operations. Attached is a minimal example: I <b=
r>
create a sphere, warp it along the normals, scale the normals, warp it <br>
again using the already existing warp filter (here the scaling is not <br>
taken into account for some reason), and warp it using a new warp filter <b=
r>
(here it is, but I guess it creates a new object instead of modifying <br>
the existing one, right?). This seem like a trivial issue, but I cannot <br=
>
seem to figure it out. Can someone help me? Thank you so much.<br>
<br>
Martin<br>
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</blockquote></div>
</div></div>

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