I would like to visualise a VTK data file (OpenFOAM output) using python. The plot I would like to make is a 1-d line plot of a quantity between two endpoints. To do so, the unstructured data should be interpolated on the points which lie between the two endpoints.

I've used the package Mayavi to visualise the VTK data. At the mayavi webpage there is a description of probing a single value from a scalarfield. This function does not work on a VTK file.

Also I've found a delaunay3d method (mlab.pipeline.delaunay3d) at the mayavi webpage. I did not get this one to work either.

Could anyone advise me how to interpolate my data?

Eventually, I found the answer to my own question. Just in case anyone visits this topic ans has the same problems, I will post my solution. I've used the vtkProbeFilter to interpolate my VTK-data. After the interpolation I've transformed the VTK-line to a numpy array for plotting convenience.

#!/usr/bin/env python
import numpy as np
from vtk.util import numpy_support as VN
from matplotlib import pyplot as plt
import vtkdef readVTK(filename):#read the vtk file with an unstructured gridreader = vtk.vtkUnstructuredGridReader()reader.SetFileName(filename)reader.ReadAllVectorsOn()reader.ReadAllScalarsOn()reader.Update()return readerdef createLine(p1,p2,numPoints):# Create the line along which you want to sampleline = vtk.vtkLineSource()line.SetResolution(numPoints)line.SetPoint1(p1)line.SetPoint2(p2)line.Update()return linedef probeOverLine(line,reader):#Interpolate the data from the VTK-file on the created line.data = reader.GetOutput()# vtkProbeFilter, the probe line is the input, and the underlying dataset is the source.probe = vtk.vtkProbeFilter()probe.SetInputConnection(line.GetOutputPort())probe.SetSource(data)probe.Update()#get the data from the VTK-object (probe) to an numpy arrayq=VN.vtk_to_numpy(probe.GetOutput().GetPointData().GetArray('U'))numPoints = probe.GetOutput().GetNumberOfPoints() # get the number of points on the line#intialise the points on the line    x = np.zeros(numPoints)y = np.zeros(numPoints)z = np.zeros(numPoints)points = np.zeros((numPoints , 3))#get the coordinates of the points on the linefor i in range(numPoints):x[i],y[i],z[i] = probe.GetOutput().GetPoint(i)points[i,0]=x[i]points[i,1]=y[i]points[i,2]=z[i]return points,qdef setZeroToNaN(array):# In case zero-values in the data, these are set to NaN.array[array==0]=np.nanreturn array#Define the filename of VTK file
filename='a-VTK-file.vtk'#Set the points between which the line is constructed.
p1=[0.0,-0.1,0.0]
p2=[0.0,-0.1,1.0]#Define the numer of interpolation points
numPoints=100reader = readVTK(filename) # read the VTKfile
line=createLine(p1,p2,numPoints) # Create the line
points,U =  probeOverLine(line,reader) # interpolate the data over the lineU = setZeroToNaN(U) # Set the zero's to NaN's
plt.plot(points[:,2],U[:,0]) #plot the data
plt.show()