How to merge vtk files?

Support
1

Dear all,

I have two vtk files obtained after the simulation that needs to be merged for visualization.

I saw a post related to this where vtkAppendPolyData() function is used. I tried in this way, but gave me an error.

import vtk
from vtk import vtkAppendPolyData, vtkPolyDataReader, vtkPolyDataWriter

a = vtkAppendPolyData()
a.AddInput('file1.vtk')
a.AddInput('file2.vtk')

AttributeError: ‘vtkmodules.vtkFiltersCore.vtkAppendPolyData’ object has no attribute 'AddInput’

What attributes do I need to give so as to merge the vtk files?

Regards,

Sunag R A.

2

Please see https://kitware.github.io/vtk-examples/site/Cxx/Filtering/CombinePolyData/ for an example of how to do this.

3

Dear Cory,

Thank you very much for the info.

I managed to merged the vtk files. But I am unable to visualize the output vtk file although it contains all the data.

The code structure goes like this.

import vtk

from vtk import vtkAppendPolyData, vtkPolyDataReader, vtkPolyDataWriter, vtkPolyData, vtkUnstructuredGridReader

reader = vtkUnstructuredGridReader()#vtkPolyDataReader()
append = vtkAppendPolyData()

filenames = ['file1.vtk', 'file2.vtk']
for file in filenames:
    reader.SetFileName(file)
    reader.Update()
    polydata = vtkPolyData()
    polydata.ShallowCopy(reader.GetOutput())
    append.AddInputData(polydata)

append.Update()    

writer = vtkPolyDataWriter()
writer.SetFileName('output.vtk')
writer.SetInputData(append.GetOutput())
writer.Write()

I am unable to visualize the “output.vtk” file. I think below might be the possible issue?

  1. The output.vtk created has a version of 5.1 while the file1 and file2 has a version of 2.0.
  2. The file1 and file2 vtk has a name as “DATASET UNSTRUCTURED_GRID” while output.vtk has a name of “DATASET POLYDATA” in its file.

If so, how to make it work?

File1 vtk:

# vtk DataFile Version 2.0
simulation
ASCII
DATASET UNSTRUCTURED_GRID
POINTS 283933 float

output vtk

# vtk DataFile Version 5.1
vtk output
ASCII
DATASET POLYDATA
POINTS 284154 float

For reference, I have attached the link to File1 and File2 vtk files.

file1 and file2

4

Replace vtkAppendPolyData with vtkAppendFilter. vtkAppendPolyData works only with vtkPolyData inputs, but you have vtkUnstructuredGrid datasets. Hence you need to use the more general vtkAppendFilter.

1 Like
5

Dear Cory,

Thanks for the reply. I changed vtkAppendPolyData with vtkAppendFilter. But I am still unable to see visualization even after saving with Unstructured Grid. Below is the latest code changes.

from vtk import vtkAppendFilter, vtkUnstructuredGridWriter, vtkPolyData, vtkUnstructuredGridReader

reader = vtkUnstructuredGridReader()
append = vtkAppendFilter()

filenames = ['file1.vtk', 'file2.vtk']
for file in filenames:
    reader.SetFileName(file)
    reader.Update()
    polydata = vtkPolyData()
    polydata.ShallowCopy(reader.GetOutput())
    append.AddInputData(polydata)

append.Update()    

writer = vtkUnstructuredGridWriter()
#writer = vtkPolyDataWriter()
writer.SetFileName('output.vtk')
writer.SetInputData(append.GetOutput())
writer.Write()

Regards,
Sunag R A.

6

Also discussed in this cross post

1 Like
7

Could you clarify what you mean and what you are expecting? Do you expect to be able to see a visualization after calling writer.Write()? If so, you current code will not create a visualization.

Or are you trying to view output.vtk in another program, and the output is empty?

8

I was trying to view the output.vtk in paraview. The output was not empty, but visually it was not rendering. There was a data loading problem. As suggested by Nicolas, I changed the data loading code and now its rendering well. Below are the changes.

- polydata = vtkPolyData()
- polydata.ShallowCopy(reader.GetOutput())
+ unstructured = vtkUnstructuredGrid()
+ unstructured.ShallowCopy(reader.GetOutput())

Regards,
Sunag R A.