Vector data not identified as VECTORS

Description

I’m a bit of a VTK newbie, so I didn’t want to post this for sure as a bug. But there’s something strange going on with assigning point data. The pyvista sphere example provides a minimal working example of what happens, so no data is needed:

sphere = pv.Sphere(radius=3.14)
vectors = np.vstack(
    (
        np.sin(sphere.points[:, 0]),
        np.cos(sphere.points[:, 1]),
        np.cos(sphere.points[:, 2]),
    )
).T
sphere.vectors = vectors * 0.3
sphere.arrows.plot(scalars='GlyphScale')

All of this, of course, works fine. However, suppose you try to save this data in ascii format:

sphere.save('sphere.vtk', binary=False)

If you open the resulting file in a text editor and scroll down to the POINT_DATA field, you get something that to me was rather unexpected:

POINT_DATA 842
SCALARS _vectors float 3
LOOKUP_TABLE default

So, it’s recording the vector data as scalar data with the name “_vectors”, type float, and 3 components (I’m referencing the vtk.org guidance on file-formats). This to me is rather weird. I was expecting a VECTOR dataset attribute with some kind of default name (I’m not sure how one assigns a name to vector data in the pyvista API). Something like:

POINT_DATA 842
VECTORS vectors float

I’m decently sure this is a bug because causes problems down the line: if I try to open this vtk file in something like VisIt to do a vector glyph plot, it can’t find the vector data. But maybe there’s some other way you are supposed to accomplish assigning vector point data? I thought the sphere example was a great showcase of how this should be done, but then there’s this weird formatting issue. Any help/guidance would be greatly appreciated!

[mountaindust]

Info about a workaround I am currently using:

I can currently find no way to set VECTOR data in pyvista without resorting to the underlying VTK API. For the moment, here is what I am doing in order to get VECTOR data. This code follows the sphere example in the original post:

from vtk.util import numpy_support
vectors_vtk = numpy_support.numpy_to_vtk(vectors)
vectors_vtk.SetName('myvectors') # name for the dataset, to replace the default 'vectors'
sphere_pt_data = sphere.GetPointData()
sphere_pt_data.SetVectors(vectors_vtk)
sphere.save('sphere.vtk', binary=False)

[MatthewFlamm]

I transferred this to the main repo as I think it has moved out of a support question and into a discussion about how to go about adding this functionality into the codebase (or whether it should be).