[Paraview] Naming an existing data array.

[Andrew Maclean]

Burlen,
   Thankyou so much for your quick response. The script works fine. I am a
bit of a ParaView novice when it comes to scripting so thanks for the help!

This problem arose because I was looking at the VTK Parametric Functions
and wondering why they looked so terrible in ParaView and yet there were no
issues displaying them in VTK.
So I wrote an XML plugin and discovered that I couldn't access the scalars
or normals. In the case of normals, for non-orientable surfaces the normals
become really important and they are generated with the surface, so you
need access the data. Paraview can do this if it knows the name of the
dataset.

It turns out that when I wrote vtkParametricFunctionSource (way back in
2003 I think!) I never named the normal or scalar arrays. So I will fix
this, modernise the code and update the documentation in this coming week.

If you are interested, here is a first attempt at the xml plugin. With your
script we get some beautiful results in Paraview. Of course I need to add
in the parameters for all the other surfaces. I have only
done ParametricConicSpiral and ParametricMobius.

First: Use Manage Plugins to import the xml script.
Then:
1) Find ParametricSource in Sources and select a function e.g Mobius,
(Minimum V = -0.2, Maximum V = 0.2) specify a scalar mode and you will get
a very ordinary mobius strip.
2) Apply your script as a programmable filter and select the coloring to be
scalars and you get a beautifully shaded surface.
3) Then apply the Glyph filter using the Normals as vectors and you get a
nice display of the vectors on the surface. Use a scale of (-1,-1,-1) if
you want to invert the normals.

You get some beautiful images.

Regards
   Andrew



On Sun, Jun 1, 2014 at 3:03 AM, Burlen Loring <bloring at lbl.gov> wrote:

>  Hi Andrew,
>
> I see a couple of things in your script. First is normals and scalars are
> data set attributes. so you need to access them through one of those
> classes, ex vtkPointData.
>
> Correct me if I'm wrong but, although in VTK 6 you generally don't need to
> shallow copy the input to filters I think it's still probably a bad
> practice to modify the arrays in the input dataset.
>
> I think what you want to do is copy the geometric structure of the input
> and then make a deep copy of normals and scalars arrays, and rename the
> copys. Copy structure rather than shallow copy since with a shallow copy
> you'd still end up modifying the arrays in the input dataset.
>
> Finally scalars and normals may not be present. I know you'd probably
> handle that in your final script, ;-)
>
> given all that, here's what I came up with:
>
> def copyAndNameArray(da, name):
>   if da is not None:
>     outda = da.NewInstance()
>     outda.DeepCopy(da)
>     outda.SetName(name)
>     return outda
>   else:
>     return None
>
>
> pdi = self.GetPolyDataInput()
> pdo = self.GetPolyDataOutput()
> pdo.CopyStructure(pdi)
>
> pdo.GetPointData().SetNormals( \
>   copyAndNameArray(pdi.GetPointData().GetNormals(), 'Normals'))
>
> pdo.GetPointData().SetScalars( \
>   copyAndNameArray(pdi.GetPointData().GetScalars(), 'Scalars'))
>
> print 'Normals=%s'%(str(pdo.GetPointData().GetNormals()))
> print 'Scalars=%s'%(str(pdo.GetPointData().GetScalars()))
>
> Curious to hear from other developers as to if I'm on target about not
> modifying arrays in the input or if this is overkill given the new VTK 6
> pipeline.
>
> Burlen
>
>
> On 05/30/2014 07:29 PM, Andrew Maclean wrote:
>
> I have a source object that produces a polydata object. Unfortunately the
> normals and scalars are unnamed. How do I access these and name them in
> ParaView.
> I thought something like this may work in a Programmable Filter:
>
>
> pdi = self.GetPolyDataInput()
>
> pdo =  self.GetPolyDataOutput()
>
> pdi.GetNormals().SetName('Normals')
>
> pdi.GetScalars().SetName('Scalars')
>
> pdo = pdi
>
>
>  However, I can't see the array names.
>
>  This sort of thing works Ok in a Python Script:
>      # Name the arrays
>
> randomHillsSource.GetOutput().GetPointData().GetNormals().SetName('Normals')
>
> randomHillsSource.GetOutput().GetPointData().GetScalars().SetName('Scalars')
> #     pd = randomHillsSource.GetOutput().GetPointData()
> #     print pd
>
>  Is it possible to do this on ParaView?
>
>  Thanks in advance for any help.
>
>  Andrew
>
>  --
> ___________________________________________
> Andrew J. P. Maclean
>
> ___________________________________________
>
>
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-- 
___________________________________________
Andrew J. P. Maclean

___________________________________________
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