# Paraview vs OpenFOAM vtp slice plotting with matplotlib
**URL:** https://discourse.paraview.org/t/paraview-vs-openfoam-vtp-slice-plotting-with-matplotlib/10941
**Category:** ParaView Support
**Created:** [December 7, 2022, 7:32pm UTC](https://discourse.paraview.org/t/paraview-vs-openfoam-vtp-slice-plotting-with-matplotlib/10941 "2022-12-07T19:32:12Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@Gabriel\_Axtmann](https://discourse.paraview.org/u/Gabriel_Axtmann)
#### Post date: [December 7, 2022, 7:32pm UTC](https://discourse.paraview.org/t/paraview-vs-openfoam-vtp-slice-plotting-with-matplotlib/10941/1 "2022-12-07T19:32:12Z")
Hi
maybe you can help me out with a right comment or hint for my problem.
Pretty easy, I would like to plot a 2D slice vtp file (OpenFOAM) via matplotlib as tricontourf plot.
1.) Creating the vtp slice by Paraview and saving as vtp file works like a charme
2.) Using the runtime vtp file, created by cuttingPlane - libsampling OpenFOAM creates a weird triangle order.
In the attachement you can find an example, including the plotting python script and the data loader.
What am I missing?
Best,
```auto
def loadVTPFile(filename):
import vtk
from vtk.util.numpy_support import vtk_to_numpy
from vtk.util import numpy_support as npvtk
reader = vtk.vtkXMLPolyDataReader()
reader.SetFileName(filename)
reader.Update()
data = reader.GetOutput()
points = data.GetPoints()
npts = points.GetNumberOfPoints()
x = vtk_to_numpy(points.GetData())
triangles= vtk_to_numpy(data.GetPolys().GetData())
ntri = triangles.size // 4 # number of cells
tri = np.take(triangles,[n for n in range(triangles.size) if n%4 != 0]).reshape(ntri,3)
n_arrays = reader.GetNumberOfPointArrays()
for i in range(n_arrays):
print(reader.GetPointArrayName(i))
X = vtk_to_numpy(points.GetData())
x=X[:,0]
y=X[:,1]
z=X[:,2]
# Define the velocity components U=(u,v,w)
U = vtk_to_numpy(data.GetPointData().GetArray('UMean'))
u = U[:,0]
v = U[:,1]
w = U[:,2]
magU=np.sqrt(u **2+v** 2+w**2)
p = vtk_to_numpy(data.GetPointData().GetArray('pMean'))
Ma = vtk_to_numpy(data.GetPointData().GetArray('MaMean'))
rho = vtk_to_numpy(data.GetPointData().GetArray('rhoMean'))
return x,y,z,u,v,w,magU,p,Ma,rho,tri
```
7
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### Author:  [@Gabriel\_Axtmann](https://discourse.paraview.org/u/Gabriel_Axtmann)
#### Post date: [December 17, 2022, 11:34am UTC](https://discourse.paraview.org/t/paraview-vs-openfoam-vtp-slice-plotting-with-matplotlib/10941/2 "2022-12-17T11:34:39Z")
No one has an idea?
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### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [December 19, 2022, 9:33am UTC](https://discourse.paraview.org/t/paraview-vs-openfoam-vtp-slice-plotting-with-matplotlib/10941/3 "2022-12-19T09:33:06Z")
This looks like a matplotlib question, not a ParaView question.
---
### Author:  [@foreverunfree](https://discourse.paraview.org/u/foreverunfree)
#### Post date: [November 9, 2023, 6:45am UTC](https://discourse.paraview.org/t/paraview-vs-openfoam-vtp-slice-plotting-with-matplotlib/10941/4 "2023-11-09T06:45:30Z")
Hi,
Have you solved the problem? I also want to know how to do the correct triangulation.