# \[HELP\] Python Plugin: How do I use vtkContourFilter / vtkGenericContourFilter?
**URL:** https://discourse.paraview.org/t/help-python-plugin-how-do-i-use-vtkcontourfilter-vtkgenericcontourfilter/2438
**Category:** Development
**Tags:** python, vtk
**Created:** [August 15, 2019, 11:56am UTC](https://discourse.paraview.org/t/help-python-plugin-how-do-i-use-vtkcontourfilter-vtkgenericcontourfilter/2438 "2019-08-15T11:56:07Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@mhinderh](https://discourse.paraview.org/u/mhinderh)
#### Post date: [August 15, 2019, 11:56am UTC](https://discourse.paraview.org/t/help-python-plugin-how-do-i-use-vtkcontourfilter-vtkgenericcontourfilter/2438/1 "2019-08-15T11:56:07Z")
Hey,
I’m relatively new to Paraview, vtk and plugin development. I’ve been looking up and down the documentation but I don’t seem to get things to work.
I need to write a plugin that has vtkImageData as input, alters the values, applies contours and then gives the contours as output. Altering the values worked and I managed to output it as vtkImageData again. However contouring doesn’t seem to work. I’ve got it to run without any compile errors but it also does nothing. The contour filter array is empty and packing it into vtkPolyData as output didn’t seem to work either.
I really hope someone here can help me or point me in the right direction because I don’t know what else to try.
Working randomization:
```python
__all__ = ['prtlRnd']
from pyprtl.util.vtkAlgorithm import *
import pyprtl.util.arrays as util
from vtkmodules.vtkCommonDataModel import vtkImageData
import numpy as np
from vtk.vtkCommonCore import vtkDoubleArray
import vtk
from short_inputarray import * # allows to write @smproperty_inputarray
import random
@smproxy.filter(label='Rnd')
@smhint_menu('prtl')
@smproperty.input(name='Input', port_index=0)
@smdomain.datatype(dataTypes=['vtkImageData'])
class prtlRnd(VTKPythonAlgorithmBase):
def __init__ (self):
#self.A = 0
self._array_field = 0
self._array_name = None
VTKPythonAlgorithmBase. __init__ (self,
nInputPorts=1, nOutputPorts=1,
inputType='vtkImageData', outputType='vtkImageData')
@smproperty_inputarray('Scalars')
def SetInputArrayToProcess(self, idx, port, connection, field, name):
self._array_field = field
self._array_name = name
self.Modified()
return 1
def RequestData(self, request, inInfo, outInfo):
# get the first input
input0 = vtkImageData.GetData(inInfo[0])
# get the output
output = vtkImageData.GetData(outInfo)
# Create an instance of vtkImageData
myVtkImageData = vtk.vtkImageData()
# Copy Structure from input:
myVtkImageData.CopyStructure(input0)
dimensions = myVtkImageData.GetDimensions()
inputArray = input0.GetPointData().GetArray(self._array_name)
#print("inputArray")
#print(type(inputArray))
# Create a data array to hold the sorted input
myVtkDataArray = vtk.vtkDoubleArray()
myVtkDataArray.SetNumberOfComponents(inputArray.GetNumberOfComponents()) # Do this before SetNumberOfTuples to request enough memory
myVtkDataArray.SetNumberOfTuples(np.prod(dimensions))
myVtkDataArray.SetName("myData")
perturbedInput = [inputArray.GetTuple(i) for i in range(inputArray.GetNumberOfTuples())]
# load list of seeds
f = open("/media/mario/Volume/Google Drive/Dropbox/Studium/Bachelorarbeit/Paraview/seeds.txt", "r")
seeds = list()
for line in f:
seeds.append(line)
if not seeds:
print("seeds is empty!")
# add random values and add to the list
# this is done ~1000 times and added to pOutList (list of list results)
pOutList = list()
while seeds:
tmp = list()
random.seed(seeds.pop())
for k in range(len(perturbedInput)):
x = perturbedInput[k][0] + random.uniform(-0.1,0.1)
tmp.append((x,))
pOutList.append(tmp)
# Fill our data array
for z in range(dimensions[2]):
for y in range(dimensions[1]):
for x in range(dimensions[0]):
index = x + y * dimensions[0] + z * dimensions[0] * dimensions[1]
myVtkDataArray.SetTuple(index, pOutList[5][index]) #isolines
# Add the array to the image data
myVtkImageData.GetPointData().AddArray(myVtkDataArray)
# copy input to output
output.ShallowCopy(myVtkImageData)
return 1
```
---
### Author:  [@ben.boeckel](https://discourse.paraview.org/u/ben.boeckel)
#### Post date: [August 15, 2019, 1:58pm UTC](https://discourse.paraview.org/t/help-python-plugin-how-do-i-use-vtkcontourfilter-vtkgenericcontourfilter/2438/2 "2019-08-15T13:58:31Z")
@mwestphal @utkarsh.ayachit
---
### Author:  [@utkarsh.ayachit](https://discourse.paraview.org/u/utkarsh.ayachit)
#### Post date: [August 17, 2019, 12:07pm UTC](https://discourse.paraview.org/t/help-python-plugin-how-do-i-use-vtkcontourfilter-vtkgenericcontourfilter/2438/3 "2019-08-17T12:07:47Z")
I am not sure what example we are looking at. I don’t see anything about contouring or `packing it into vtkPolyData`. Can you please post/comment the code appropriately. thanks.
---
### Author:  [@mhinderh](https://discourse.paraview.org/u/mhinderh)
#### Post date: [August 20, 2019, 8:43am UTC](https://discourse.paraview.org/t/help-python-plugin-how-do-i-use-vtkcontourfilter-vtkgenericcontourfilter/2438/4 "2019-08-20T08:43:49Z")
Sorry, my bad.
```
__all__ = ['prtlRnd']
from pyprtl.util.vtkAlgorithm import *
import pyprtl.util.arrays as util
from vtkmodules.vtkCommonDataModel import vtkImageData, vtkPolyData
import numpy as np
from vtk.vtkCommonCore import vtkDoubleArray
import vtk
from pyprtl.short_inputarray import * # allows to write @smproperty_inputarray
import random
@smproxy.filter(label='Rnd')
@smhint_menu('prtl')
@smproperty.input(name='Input', port_index=0)
@smdomain.datatype(dataTypes=['vtkImageData'])
class prtlRnd(VTKPythonAlgorithmBase):
def __init__ (self):
#self.A = 0
self._array_field = 0
self._array_name = None
VTKPythonAlgorithmBase. __init__ (self,
nInputPorts=1, nOutputPorts=1,
inputType='vtkImageData', outputType='vtkPolyData')
@smproperty_inputarray('Scalars')
def SetInputArrayToProcess(self, idx, port, connection, field, name):
self._array_field = field
self._array_name = name
self.Modified()
return 1
def RequestData(self, request, inInfo, outInfo):
# get the first input
input0 = vtkImageData.GetData(inInfo[0])
# get the output
#output = vtkImageData.GetData(outInfo)
output = vtkPolyData.GetData(outInfo)
# Create an instance of vtkImageData
myVtkImageData = vtk.vtkImageData()
# Copy Structure from input:
myVtkImageData.CopyStructure(input0)
dimensions = myVtkImageData.GetDimensions()
inputArray = input0.GetPointData().GetArray(self._array_name)
#print("inputArray")
#print(type(inputArray))
# Create a data array to hold the sorted input
myVtkDataArray = vtk.vtkDoubleArray()
myVtkDataArray.SetNumberOfComponents(inputArray.GetNumberOfComponents()) # Do this before SetNumberOfTuples to request enough memory
myVtkDataArray.SetNumberOfTuples(np.prod(dimensions))
myVtkDataArray.SetName("myData")
perturbedInput = [inputArray.GetTuple(i) for i in range(inputArray.GetNumberOfTuples())]
# load list of seeds
f = open("C:/Users/MarioLaptop/Google Drive/Dropbox/Studium/Bachelorarbeit/Paraview/seeds.txt", "r")
#f = open("/media/mario/Volume/Google Drive/Dropbox/Studium/Bachelorarbeit/Paraview/seeds.txt", "r")
seeds = list()
for line in f:
seeds.append(line)
if not seeds:
print("seeds is empty!")
# add random values and add to the list
# this is done ~1000 times and added to pOutList (list of list results)
pOutList = list()
while seeds:
tmp = list()
random.seed(seeds.pop())
for k in range(len(perturbedInput)):
x = perturbedInput[k][0] + random.uniform(-0.1,0.1)
tmp.append((x,))
pOutList.append(tmp)
# Fill our data array
for z in range(dimensions[2]):
for y in range(dimensions[1]):
for x in range(dimensions[0]):
index = x + y * dimensions[0] + z * dimensions[0] * dimensions[1]
myVtkDataArray.SetTuple(index, pOutList[5][index]) #isolines
# Add the array to the image data
myVtkImageData.GetPointData().AddArray(myVtkDataArray)
contour = vtk.vtkContourFilter()
contour.SetInputDataObject(0,myVtkImageData)
contour.SetInputArrayToProcess(0,0,0,0,myVtkImageData.GetPointData().GetArray(self._array_name))
contour.GenerateValues(10, 0, 2)
contour.Update()
#output.CopyStructure(contour.GetOutputDataObject(0))
output.DeepCopy(contour.GetOutputDataObject(0))
# copy input to output
#output.ShallowCopy(myVtkImageData)
return 1
```
I don’t know whether the countouring works, I get no errors, however contouring is empty. Maybe that’s how filter functions work but I also don’t get anything displayed. Are there any errors or did I just forget something?
My thought was that the access of the array of myVtkImageData is wrong:
> ```
> contour.SetInputArrayToProcess(0,0,0,0,myVtkImageData.GetPointData().GetArray(self-_array_name))
>
> ```
When printing out myVtkImageData, it says that the array is called “myData”, however if I try to use that name it say that array doesn’t exist.
---
### Author:  [@utkarsh.ayachit](https://discourse.paraview.org/u/utkarsh.ayachit)
#### Post date: [August 22, 2019, 11:45am UTC](https://discourse.paraview.org/t/help-python-plugin-how-do-i-use-vtkcontourfilter-vtkgenericcontourfilter/2438/5 "2019-08-22T11:45:02Z")
> [@mhinderh](#):
>
> contour.SetInputArrayToProcess(0, 0, 0, 0, myVtkImageData.GetPointData().GetArray(self.\_array\_name))
This is incorrect. [SetInputArrayToProcess](https://vtk.org/doc/nightly/html/classvtkAlgorithm.html#a42a55ca2c277aecc909ad592d12978aa) does not take the array as the argument, but it’s name. Your intention, I suspect, would be `contour.SetInputArrayToProcess(0, 0, 0, self. _array_field, self._array_name)` but that too may not work in your case. You’re creating a `myVtkImageData` with only 1 array named `myData`. Note you’re using ` myVtkImageData.CopyStructure(input0)` which does not copy any array from the input. If your intent was to pass input arrays, you should call `ShallowCopy` instead. Also `output.DeepCopy(contour.GetOutputDataObject(0))` is an overkill. `output.ShallowCopy(contour.GetOutputDataObject(0))` is adequate.
In other words, there are many issues with this code. I’d recommend simply using `vtkpython` (or `pvpython`) to build your pipeline using VTK python API and once you’re confirmed that works, continue to package it in a filter.