# How to use VTK filters and writers in a catalyst python pipeline?

**URL:** https://discourse.paraview.org/t/how-to-use-vtk-filters-and-writers-in-a-catalyst-python-pipeline/4913
**Category:** In Situ Support
**Created:** [July 21, 2020, 5:58pm UTC](https://discourse.paraview.org/t/how-to-use-vtk-filters-and-writers-in-a-catalyst-python-pipeline/4913 "2020-07-21T17:58:44Z")
**Posts on this page:** 5
**Page:** 1

<div class="post-metadata">

### Author: ![Seshu](https://discourse.paraview.org/user_avatar/discourse.paraview.org/seshu/32/4385_2.png) [@Seshu](https://discourse.paraview.org/u/Seshu)
#### Post date: [July 21, 2020, 5:58pm UTC](https://discourse.paraview.org/t/how-to-use-vtk-filters-and-writers-in-a-catalyst-python-pipeline/4913/1 "2020-07-21T17:58:44Z")

</div>

Continuing the discussion from [Help! How create a "depth map" using ParaView (Is it possible)](https://discourse.paraview.org/t/help-how-create-a-depth-map-using-paraview-is-it-possible/738/2):

I am trying to use script provide in the link above in a catalyst pipeline. I tried a programmable filter in paraview, but that did not seem to work in catalyst. Instead I decided to just modify the script catalyst generates and put that code in it, but I am having trouble getting it to write any data.

My pipeline has this in it:

```
ss = vtk.vtkWindowToImageFilter() 
ss.SetInputBufferTypeToZBuffer()
ss.SetInput(renderView1.SMProxy.GetRenderWindow())
writer = XMLImageDataWriter(ss.GetOutputPort())
coprocessor.RegisterWriter(writer, "z_buffer_%t.vti", 1)

```

but i see this:

> ```
> Traceback (most recent call last):
> File "<string>", line 2, in <module>
> File "./volume2.py", line 218, in DoCoProcessing
> File "//lib/python3.8/site-packages/paraview/coprocessing.py", line 212, in UpdateProducers
> self.CreatePipeline(datadescription)
> File "./volume2.py", line 169, in CreatePipeline
> File "./volume2.py", line 34, in _CreatePipeline
> File "./volume2.py", line 162, in Pipeline
> File "//lib/python3.8/site-packages/paraview/simple.py", line 2243, in CreateObject
> raise RuntimeError ("Expecting a proxy as input.")
> RuntimeError: Expecting a proxy as input.
> 
> ```

In general what is the method for using arbitrary vtk filters and writers in a catalyst pipeline? I have looked at the Custom Python Script Pipeline section in the manual but it was not clear to me.

---

<div class="post-metadata">

### Author: ![Seshu](https://discourse.paraview.org/user_avatar/discourse.paraview.org/seshu/32/4385_2.png) [@Seshu](https://discourse.paraview.org/u/Seshu)
#### Post date: [July 21, 2020, 6:39pm UTC](https://discourse.paraview.org/t/how-to-use-vtk-filters-and-writers-in-a-catalyst-python-pipeline/4913/2 "2020-07-21T18:39:17Z")

</div>

Here is the error I was seeing when trying to use vtkXMLImageDataWriter

> Traceback (most recent call last):  
> File “”, line 2, in   
> File “./volume2.py”, line 219, in DoCoProcessing  
> File “//lib/python3.8/site-packages/paraview/coprocessing.py”, line 212, in UpdateProducers  
> self.CreatePipeline(datadescription)  
> File “./volume2.py”, line 170, in CreatePipeline  
> File “./volume2.py”, line 34, in \_CreatePipeline  
> File “./volume2.py”, line 164, in Pipeline  
> File “//lib/python3.8/site-packages/paraview/coprocessing.py”, line 489, in RegisterWriter  
> writer.add\_attribute(“parameters”, writerParametersProxy)  
> AttributeError: ‘vtkmodules.vtkIOXML.vtkXMLImageDataWriter’ object has no attribute ‘add\_attribute’

Corresponding code:

> ss = vtk.vtkWindowToImageFilter()  
> ss.SetInputBufferTypeToZBuffer()  
> ss.SetInput(renderView1.SMProxy.GetRenderWindow())  
> writer = vtk.vtkXMLImageDataWriter()  
> writer.SetInputConnection(ss.GetOutputPort())  
> coprocessor.RegisterWriter(writer, “z\_buffer\_%t.vti”, 1)

---

<div class="post-metadata">

### Author: ![Seshu](https://discourse.paraview.org/user_avatar/discourse.paraview.org/seshu/32/4385_2.png) [@Seshu](https://discourse.paraview.org/u/Seshu)
#### Post date: [July 22, 2020, 3:40am UTC](https://discourse.paraview.org/t/how-to-use-vtk-filters-and-writers-in-a-catalyst-python-pipeline/4913/3 "2020-07-22T03:40:04Z")

</div>

I tried a ProgrammableFilter again. Using this as the script:

```
      import vtk                                                                                                                                                                                                                           
      from paraview.simple import GetActiveView                                                                                                                                                                                            
      ss = vtk.vtkWindowToImageFilter()                                                                                                                                                                                                    
      ss.SetShouldRerender(True)                                                                                                                                                                                                           
      ss.SetInputBufferTypeToZBuffer()                                                                                                                                                                                                     
      ss.SetInput(GetActiveView().SMProxy.GetRenderWindow())                                                                                                                                                                               
      ss.Update()                                                                                                                                                                                                                          
      output = ss.GetOutput()

```

but it seems to seg fault due to the call to Update(), if I don’t call update the filter never seems to produce any output:

> Loguru caught a signal: SIGSEGV  
> Stack trace:  
> [truncated]  
> 123 0x7f3d9206aca2 vtkCompositeDataPipeline::ForwardUpstream(vtkInformation\*) + 386  
> 122 0x7f3d920b1411 vtkStreamingDemandDrivenPipeline::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 881  
> 121 0x7f3d92071bbf vtkDemandDrivenPipeline::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 1343  
> 120 0x7f3d9206be51 vtkCompositeDataPipeline::ExecuteData(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 129  
> 119 0x7f3d9206eee9 vtkDemandDrivenPipeline::ExecuteData(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 57  
> 118 0x7f3d92074bc0 vtkExecutive::CallAlgorithm(vtkInformation\*, int, vtkInformationVector\*\*, vtkInformationVector\*) + 80  
> 117 0x7f3d914b3470 vtkPythonProgrammableFilter::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 16  
> 116 0x7f3d8f42713d vtkProgrammableFilter::RequestData(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 61  
> 115 0x7f3d914b2de0 vtkPythonProgrammableFilter::Exec(char const\*, char const\*) + 5568  
> 114 0x7f3d9bab949f vtkPythonInterpreter::RunSimpleString(char const\*) + 335  
> 113 0x7f3d9b8f12fd PyRun\_SimpleStringFlags + 61  
> 112 0x7f3d9b8f13ad PyRun\_StringFlags + 125  
> 111 0x7f3d9b8f4483 /usr/lib/libpython3.8.so.1.0(+0x1d2483) [0x7f3d9b8f4483]  
> 110 0x7f3d9b8fa248 /usr/lib/libpython3.8.so.1.0(+0x1d8248) [0x7f3d9b8fa248]  
> 109 0x7f3d9b8eeb03 PyEval\_EvalCode + 35  
> 108 0x7f3d9b83e654 \_PyEval\_EvalCodeWithName + 772  
> 107 0x7f3d9b83fd08 \_PyEval\_EvalFrameDefault + 920  
> 106 0x7f3d9b85087d \_PyFunction\_Vectorcall + 413  
> 105 0x7f3d9b83e654 \_PyEval\_EvalCodeWithName + 772  
> 104 0x7f3d9b844a78 \_PyEval\_EvalFrameDefault + 20744  
> 103 0x7f3d9b84918c \_PyObject\_MakeTpCall + 1116  
> 102 0x7f3d9b8569ea PyCFunction\_Call + 410  
> 101 0x7f3cf29b4ab1 //lib/python3.8/site-packages/vtkmodules/vtkCommonExecutionModel.so(+0x2bab1) [0x7f3cf29b4ab1]  
> 100 0x7f3d920b27a7 vtkStreamingDemandDrivenPipeline::Update(int, vtkInformationVector\*) + 279  
> 99 0x7f3d920b1411 vtkStreamingDemandDrivenPipeline::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 881  
> 98 0x7f3d92071bbf vtkDemandDrivenPipeline::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 1343  
> 97 0x7f3d9206be51 vtkCompositeDataPipeline::ExecuteData(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 129  
> 96 0x7f3d9206eee9 vtkDemandDrivenPipeline::ExecuteData(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 57  
> 95 0x7f3d92074bc0 vtkExecutive::CallAlgorithm(vtkInformation\*, int, vtkInformationVector\*\*, vtkInformationVector\*) + 80  
> 94 0x7f3d8e045661 vtkWindowToImageFilter::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 161  
> 93 0x7f3d8e044e4b vtkWindowToImageFilter::RequestData(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 4123  
> 92 0x7f3d9b123372 /usr/lib/libvtkCommonCore-pv5.8.so.1(+0x4cc372) [0x7f3d9b123372]  
> 91 0x7f3d910c3a9f vtkSMViewProxy::StillRender() + 143  
> 90 0x7f3d910c307e vtkSMViewProxy::Update() + 334  
> 89 0x7f3d925f24e4 vtkPVSessionBase::ExecuteStream(unsigned int, vtkClientServerStream const&, bool) + 52  
> 88 0x7f3d925f44b2 vtkPVSessionCore::ExecuteStreamInternal(vtkClientServerStream const&, bool) + 242  
> 87 0x7f3d8a9caafd vtkClientServerInterpreter::ProcessStream(vtkClientServerStream const&) + 29  
> 86 0x7f3d8a9ca64e vtkClientServerInterpreter::ProcessOneMessage(vtkClientServerStream const&, int) + 190  
> 85 0x7f3d8a9ca535 vtkClientServerInterpreter::ProcessCommandInvoke(vtkClientServerStream const&, int) + 1173  
> 84 0x7f3d92b5514d vtkPVRenderViewCommand(vtkClientServerInterpreter\*, vtkObjectBase\*, char const\*, vtkClientServerStream const&, vtkClientServerStream&, void\*) + 23053  
> 83 0x7f3d91042ed5 vtkPVRenderView::Update() + 149  
> 82 0x7f3d9105671c vtkPVView::Update() + 268  
> 81 0x7f3d91054b8f vtkPVView::CallProcessViewRequest(vtkInformationRequestKey\*, vtkInformation\*, vtkInformationVector\*) + 159  
> 80 0x7f3d90fc5d76 vtkGeometryRepresentationWithFaces::ProcessViewRequest(vtkInformationRequestKey\*, vtkInformation\*, vtkInformation\*) + 22  
> 79 0x7f3d90fc3c09 vtkGeometryRepresentation::ProcessViewRequest(vtkInformationRequestKey\*, vtkInformation\*, vtkInformation\*) + 25  
> 78 0x7f3d910083af vtkPVDataRepresentation::ProcessViewRequest(vtkInformationRequestKey\*, vtkInformation\*, vtkInformation\*) + 239  
> 77 0x7f3d920b27a7 vtkStreamingDemandDrivenPipeline::Update(int, vtkInformationVector\*) + 279  
> 76 0x7f3d920b1411 vtkStreamingDemandDrivenPipeline::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 881  
> 75 0x7f3d920717aa vtkDemandDrivenPipeline::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 298  
> 74 0x7f3d9206aca2 vtkCompositeDataPipeline::ForwardUpstream(vtkInformation\*) + 386  
> 73 0x7f3d920b1411 vtkStreamingDemandDrivenPipeline::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 881  
> 72 0x7f3d920717aa vtkDemandDrivenPipeline::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 298  
> 71 0x7f3d9206aca2 vtkCompositeDataPipeline::ForwardUpstream(vtkInformation\*) + 386  
> 70 0x7f3d920b1411 vtkStreamingDemandDrivenPipeline::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 881  
> 69 0x7f3d92071bbf vtkDemandDrivenPipeline::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 1343  
> 68 0x7f3d9206be51 vtkCompositeDataPipeline::ExecuteData(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 129  
> 67 0x7f3d9206eee9 vtkDemandDrivenPipeline::ExecuteData(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 57  
> 66 0x7f3d92074bc0 vtkExecutive::CallAlgorithm(vtkInformation\*, int, vtkInformationVector\*\*, vtkInformationVector\*) + 80  
> 65 0x7f3d914b3470 vtkPythonProgrammableFilter::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 16  
> 64 0x7f3d8f42713d vtkProgrammableFilter::RequestData(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 61  
> 63 0x7f3d914b2de0 vtkPythonProgrammableFilter::Exec(char const\*, char const\*) + 5568  
> 62 0x7f3d9bab949f vtkPythonInterpreter::RunSimpleString(char const\*) + 335  
> 61 0x7f3d9b8f12fd PyRun\_SimpleStringFlags + 61  
> 60 0x7f3d9b8f13ad PyRun\_StringFlags + 125  
> 59 0x7f3d9b8f4483 /usr/lib/libpython3.8.so.1.0(+0x1d2483) [0x7f3d9b8f4483]  
> 58 0x7f3d9b8fa248 /usr/lib/libpython3.8.so.1.0(+0x1d8248) [0x7f3d9b8fa248]  
> 57 0x7f3d9b8eeb03 PyEval\_EvalCode + 35  
> 56 0x7f3d9b83e654 \_PyEval\_EvalCodeWithName + 772  
> 55 0x7f3d9b83fd08 \_PyEval\_EvalFrameDefault + 920  
> 54 0x7f3d9b85087d \_PyFunction\_Vectorcall + 413  
> 53 0x7f3d9b83e654 \_PyEval\_EvalCodeWithName + 772  
> 52 0x7f3d9b844a78 \_PyEval\_EvalFrameDefault + 20744  
> 51 0x7f3d9b84918c \_PyObject\_MakeTpCall + 1116  
> 50 0x7f3d9b8569ea PyCFunction\_Call + 410  
> 49 0x7f3cf29b4ab1 //lib/python3.8/site-packages/vtkmodules/vtkCommonExecutionModel.so(+0x2bab1) [0x7f3cf29b4ab1]  
> 48 0x7f3d920b27a7 vtkStreamingDemandDrivenPipeline::Update(int, vtkInformationVector\*) + 279  
> 47 0x7f3d920b1411 vtkStreamingDemandDrivenPipeline::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 881  
> 46 0x7f3d92071bbf vtkDemandDrivenPipeline::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 1343  
> 45 0x7f3d9206be51 vtkCompositeDataPipeline::ExecuteData(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 129  
> 44 0x7f3d9206eee9 vtkDemandDrivenPipeline::ExecuteData(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 57  
> 43 0x7f3d92074bc0 vtkExecutive::CallAlgorithm(vtkInformation\*, int, vtkInformationVector\*\*, vtkInformationVector\*) + 80  
> 42 0x7f3d8e045661 vtkWindowToImageFilter::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 161  
> 41 0x7f3d8e044e4b vtkWindowToImageFilter::RequestData(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 4123  
> 40 0x7f3d9b123372 /usr/lib/libvtkCommonCore-pv5.8.so.1(+0x4cc372) [0x7f3d9b123372]  
> 39 0x7f3d910c3a9f vtkSMViewProxy::StillRender() + 143  
> 38 0x7f3d910c307e vtkSMViewProxy::Update() + 334  
> 37 0x7f3d925f24e4 vtkPVSessionBase::ExecuteStream(unsigned int, vtkClientServerStream const&, bool) + 52  
> 36 0x7f3d925f44b2 vtkPVSessionCore::ExecuteStreamInternal(vtkClientServerStream const&, bool) + 242  
> 35 0x7f3d8a9caafd vtkClientServerInterpreter::ProcessStream(vtkClientServerStream const&) + 29  
> 34 0x7f3d8a9ca64e vtkClientServerInterpreter::ProcessOneMessage(vtkClientServerStream const&, int) + 190  
> 33 0x7f3d8a9ca535 vtkClientServerInterpreter::ProcessCommandInvoke(vtkClientServerStream const&, int) + 1173  
> 32 0x7f3d92b5514d vtkPVRenderViewCommand(vtkClientServerInterpreter\*, vtkObjectBase\*, char const\*, vtkClientServerStream const&, vtkClientServerStream&, void\*) + 23053  
> 31 0x7f3d91042ed5 vtkPVRenderView::Update() + 149  
> 30 0x7f3d9105671c vtkPVView::Update() + 268  
> 29 0x7f3d91054b8f vtkPVView::CallProcessViewRequest(vtkInformationRequestKey\*, vtkInformation\*, vtkInformationVector\*) + 159  
> 28 0x7f3d90fc5d76 vtkGeometryRepresentationWithFaces::ProcessViewRequest(vtkInformationRequestKey\*, vtkInformation\*, vtkInformation\*) + 22  
> 27 0x7f3d90fc3c09 vtkGeometryRepresentation::ProcessViewRequest(vtkInformationRequestKey\*, vtkInformation\*, vtkInformation\*) + 25  
> 26 0x7f3d910083af vtkPVDataRepresentation::ProcessViewRequest(vtkInformationRequestKey\*, vtkInformation\*, vtkInformation\*) + 239  
> 25 0x7f3d920b27a7 vtkStreamingDemandDrivenPipeline::Update(int, vtkInformationVector\*) + 279  
> 24 0x7f3d920b1411 vtkStreamingDemandDrivenPipeline::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 881  
> 23 0x7f3d920717aa vtkDemandDrivenPipeline::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 298  
> 22 0x7f3d9206aca2 vtkCompositeDataPipeline::ForwardUpstream(vtkInformation\*) + 386  
> 21 0x7f3d920b1411 vtkStreamingDemandDrivenPipeline::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 881  
> 20 0x7f3d920717aa vtkDemandDrivenPipeline::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 298  
> 19 0x7f3d9206aca2 vtkCompositeDataPipeline::ForwardUpstream(vtkInformation\*) + 386  
> 18 0x7f3d920b1411 vtkStreamingDemandDrivenPipeline::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 881  
> 17 0x7f3d92071bbf vtkDemandDrivenPipeline::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 1343  
> 16 0x7f3d9206be51 vtkCompositeDataPipeline::ExecuteData(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 129  
> 15 0x7f3d9206eee9 vtkDemandDrivenPipeline::ExecuteData(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 57  
> 14 0x7f3d92074bc0 vtkExecutive::CallAlgorithm(vtkInformation\*, int, vtkInformationVector\*\*, vtkInformationVector\*) + 80  
> 13 0x7f3d914b3470 vtkPythonProgrammableFilter::ProcessRequest(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 16  
> 12 0x7f3d8f42713d vtkProgrammableFilter::RequestData(vtkInformation\*, vtkInformationVector\*\*, vtkInformationVector\*) + 61  
> 11 0x7f3d914b2de0 vtkPythonProgrammableFilter::Exec(char const\*, char const\*) + 5568  
> 10 0x7f3d9bab949f vtkPythonInterpreter::RunSimpleString(char const\*) + 335  
> 9 0x7f3d9b8f12fd PyRun\_SimpleStringFlags + 61  
> 8 0x7f3d9b8f138c PyRun\_StringFlags + 92  
> 7 0x7f3d9b8f16e4 PyParser\_ASTFromStringObject + 164  
> 6 0x7f3d9b86d8e4 PyAST\_FromNodeObject + 308  
> 5 0x7f3d9b86e2b0 /usr/lib/libpython3.8.so.1.0(+0x14c2b0) [0x7f3d9b86e2b0]  
> 4 0x7f3d9b870f78 /usr/lib/libpython3.8.so.1.0(+0x14ef78) [0x7f3d9b870f78]  
> 3 0x7f3d9b86fab7 /usr/lib/libpython3.8.so.1.0(+0x14dab7) [0x7f3d9b86fab7]  
> 2 0x7f3d9b784e5d /usr/lib/libpython3.8.so.1.0(+0x62e5d) [0x7f3d9b784e5d]  
> 1 0x7f3d9b9498cd \_PyUnicode\_Ready + 29  
> 0 0x7f3d9a86d960 /usr/lib/libpthread.so.0(+0x14960) [0x7f3d9a86d960]  
> ( 3.269s) [7C462E80] :0 FATL| Signal: SIGSEGV

---

<div class="post-metadata">

### Author: ![Dave\_DeMarle](https://discourse.paraview.org/user_avatar/discourse.paraview.org/dave_demarle/32/27_2.png) [@Dave\_DeMarle](https://discourse.paraview.org/u/Dave_DeMarle)
#### Post date: [July 22, 2020, 10:00pm UTC](https://discourse.paraview.org/t/how-to-use-vtk-filters-and-writers-in-a-catalyst-python-pipeline/4913/4 "2020-07-22T22:00:42Z")

</div>

I don’t advise using the vtk level directly inside a catalyst Python script because it can be tricky to get things to work correctly within the MPI parallel context. It can be done but there can be problems.

In this case I believe the best way to get a depth map is instead to get the active view and then call CaptureDepthBuffer() on it.

---

<div class="post-metadata">

### Author: ![Seshu](https://discourse.paraview.org/user_avatar/discourse.paraview.org/seshu/32/4385_2.png) [@Seshu](https://discourse.paraview.org/u/Seshu)
#### Post date: [July 23, 2020, 6:07am UTC](https://discourse.paraview.org/t/how-to-use-vtk-filters-and-writers-in-a-catalyst-python-pipeline/4913/5 "2020-07-23T06:07:52Z")

</div>

I’m not using MPI and do not plan to (I specifically built paraview without MPI).

I was actually able to get this to work:

> ```
> view = GetActiveView()
> ss = vtk.vtkWindowToImageFilter()
> ss.SetInputBufferTypeToZBuffer()
> ss.SetInput(view.SMProxy.GetRenderWindow())
> ss.Update()
> writer = vtk.vtkXMLImageDataWriter()
> writer.SetInputConnection(ss.GetOutputPort())
> writer.SetFileName("z_buffer_%02d.vti" % view.ViewTime)
> writer.Write()
> 
> ```

by putting the above code in DoCoProcessing. If I wanted to use CaptureDepthBuffer() where would it go?

I tried putting something like that (CaptureDepthBuffer) in the Pipeline class itself and using ImageDataUniformGrid but I couldn’t figure out how to write it to a file. I was still getting expecting a proxy as input error when I passed the ImageDataUniformGrid to XMLImageDataWriter.

I’d really like to understand what the process is for writing a custom pipeline in python, but I don’t understand how the API works.