[Paraview] Fwd: Python Calculator: create a multi-component field

[Christophe Bourcier]

Thank you Berk for your answer.

You are right, make_vector is even mentioned in some parts of the Paraview
Guide that I have read. But my first need was to create a 9-component field
to be able to use the Tensor Glyph filter, so I still have to use numpy.

To reproduce the bug:
- create a source sphere
- create a filter Python Calculator with this formula:
numpy.column_stack((Normals[:,0], Normals[:,1], Normals[:,2])) and Apply.
- display the field result
- in the toolbar, click on Magnitude to see the components: X, Y, Z. It is
OK.
- edit the formula of the Python Calculator with a formula that changes the
number of components: numpy.column_stack((Normals[:,0], Normals[:,1],
Normals[:,2], Normals[:,0])) and Apply without changing the name of the
result field.
- in the toolbar, click on Magnitude to see the components: X, Y, Z. It is
not OK.
- in the panel Information, the field "result" has 4 components. It is OK.
- edit the name of the result field to call it result2 and Apply.
- display the field result2, and click on Magnitude to see the components:
0, 1, 2, 3. It is OK.

So it seems to be a bug in the drop down button to select the component
that is not updated when the formula changes the number of components on an
existing field.

Christophe

2015-04-02 17:01 GMT+02:00 Berk Geveci <berk.geveci at kitware.com>:

> Dear Christophe,
>
> It seems like the documentation got out of date. Thank you for reporting
> it. There is also a make_vector() function now. You can pass it 2 or 3
> components:
>
> def make_vector(arrayx, arrayy, arrayz=None):
>     """Given 2 or 3 scalar arrays, returns a vector array. If only
>     2 scalars are provided, the third component will be set to 0."""
>
>
> I defer to Utkarsh to explain how to contribute to the tex documentation.
> It is definitely very welcome.
>
> Finally, I am not sure that I understand the comment about the potential
> bug. Can you please give the steps to reproduce?
>
> Thanks,
> -berk
>
> On Thu, Apr 2, 2015 at 5:23 AM, Christophe Bourcier <
> christophe.bourcier.pv at gmail.com> wrote:
>
>> Dear Paraview folks,
>>
>> It seems there is a mistake in the Paraview User's Guide at the end of
>> the section Python Calculator.
>>
>> To create a multi-component field from multiple scalar fields, hstack
>> used to work before Paraview 4.2.0.
>>
>> But since Paraview 4.2.0, we must use numpy.column_stack. This change may
>> have been caused by the great work done in 4.2.0 to be able to use numpy
>> arrays as vtk arrays with automatic conversion from numpy to vtk and
>> inversely.
>>
>> Using hstack will create a dataset with many components (number of nodes
>> times the number of field in hstack).
>>
>> For instance, create a sphere source with default properties.
>>
>> In Paraview 4.1.0, use this formula to create the same field as Normals:
>> hstack((Normals[:,0], Normals[:,1], Normals[:,2]))
>>
>> In Paraview 4.2.0 and 4.3.1, if you use numpy.hstack((Normals[:,0],
>> Normals[:,1], Normals[:,2])), you will get a field with 150 components,
>> since the default sphere has 50 points. And it may lead to a memory
>> oversize for a source with thousands points.
>>
>> In Paraview 4.2.0 and 4.3.1, the following formula gives the wanted
>> result:
>> numpy.column_stack((Normals[:,0], Normals[:,1], Normals[:,2]))
>>
>> Note that you must change the name of the result, otherwise the number of
>> components is not updated between two different formulas. This might be a
>> bug.
>>
>> I have not found where the latex documentation is. Is it available
>> somewhere as a git repository? What is the policy on contributing to it?
>>
>> Christophe
>>
>>
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