failed to read vtk data

[zhang-qiang-github]

Describe the bug
I want to convert a vtkPolyData into su2 file. So, firstly, I write this vtkPolyData into vtk file. Then, I want to use meshio.read to read this file and write into su2 file. However, meshiio.read failed.

To Reproduce

import vtkmodules.all as vtk

cone = vtk.vtkConeSource()
cone.Update()

writer = vtk.vtkPolyDataWriter()
writer.SetInputData(cone.GetOutput())
writer.SetFileName('test.vtk')
writer.Update()
writer.Write()

import meshio
mesh = meshio.read('test.vtk')
mesh.write('test.su2')

It report bug: Error: Couldn't read file test.vtk as vtk.

Then, I look into the code, and I find that:
Only VTK 'UNSTRUCTURED_GRID, STRUCTURED_POINTS, STRUCTURED_GRID' supported (not polydata)

So, I convert my vtkpolydata into unstructed_grid by:

data = vtk.vtkUnstructuredGrid()
data.ShallowCopy(cone.GetOutput())

The final code is:

import vtkmodules.all as vtk
cone = vtk.vtkConeSource()
cone.Update()
data = vtk.vtkUnstructuredGrid()
data.ShallowCopy(cone.GetOutput())

writer = vtk.vtkUnstructuredGridWriter()
writer.SetInputData(data)
writer.SetFileName('test.vtk')
writer.Update()
writer.Write()

import meshio
mesh = meshio.read('test.vtk')
mesh.write('test.su2')

But it still reports Couldn't read file test.vtk as vtk.
When I look into meshio code, it report required section CELLS not found.

Diagnose
The package version is:

win10 
python 3.7
vtk 9.1.0
meshio 5.3.4

Any suggestion is appreciated~~~

[nschloe]

Do you really have mesh without cells?

[nschloe]

This should be fixed in the next release.