# How to add a reference line in visualization?

**URL:** https://discourse.paraview.org/t/how-to-add-a-reference-line-in-visualization/10781
**Category:** ParaView Support
**Tags:** python, vtk
**Created:** [November 17, 2022, 6:53am UTC](https://discourse.paraview.org/t/how-to-add-a-reference-line-in-visualization/10781 "2022-11-17T06:53:47Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![axelwang](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/a/6a8cbe/32.png) [@axelwang](https://discourse.paraview.org/u/axelwang)
#### Post date: [November 17, 2022, 6:53am UTC](https://discourse.paraview.org/t/how-to-add-a-reference-line-in-visualization/10781/1 "2022-11-17T06:53:47Z")

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Hey,  
I want to simply add a reference line in my model like the following (where the line is hand-drawn):

 ![Screen Shot 2022-11-16 at 22.42.38](https://discourse.paraview.org/uploads/default/original/2X/6/6588e7d9fc04a5215aab33336a8c721fe06a46f6.png)

I have x, y, z coordinates of the line, and from what I can find about `pyvtk` it seems `pyvtk.RectilinearGrid` is a good choise, so I have the following python code:

```auto
vtk_file = destDir + "example.vtk"
exampleCurve = pyvtk.RectilinearGrid(x,y,z)
vtk = pyvtk.VtkData(exampleCurve,"")
vtk.tofile(vtk_file,'binary')

```

When I open the vtk file produced in paraview, the following is what I get.

 ![Screen Shot 2022-11-16 at 22.50.39](https://discourse.paraview.org/uploads/default/original/2X/3/3073d3363020a37db078e68c26af76b08d5fbabf.png)

It seems I can only view this as an outline, and if I click any other forms of representation, ParaView immediately crashes.

Please note that I simply wanted to plot a structure, so `pyvtk.VtkData(exampleCurve,"")` does not provide any field data on to the curve.

I have two questions now.

- What is the best way to plot a reference line/curve or any structure without field data in paraview?

- What is a good reference to learn more about pyvtk. I didn’t find any good resourced or even documentation online.

---

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### Author: ![cory.quammen](https://discourse.paraview.org/user_avatar/discourse.paraview.org/cory.quammen/32/11193_2.png) [@cory.quammen](https://discourse.paraview.org/u/cory.quammen)
#### Post date: [November 17, 2022, 11:20am UTC](https://discourse.paraview.org/t/how-to-add-a-reference-line-in-visualization/10781/2 "2022-11-17T11:20:37Z")

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> [@axelwang](#):
>
> What is the best way to plot a reference line/curve or any structure without field data in paraview?

RectilinearGrid is a good choice _if_ you have a grid of points. You have a curve, so a better choice would be a PolyData object with either a series of line segment cells or a polyline.

> [@axelwang](#):
>
> What is a good reference to learn more about pyvtk. I didn’t find any good resourced or even documentation online.

PyVTK is a separate [project](https://github.com/pearu/pyvtk) from ParaView. It looks like it hasn’t been maintained in 5 years, so I’m not sure where you could seek support.

[PyVista](https://docs.pyvista.org/) on the other hand, is under active development and has a large community. I recommend using that instead of PyVTK.

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<div class="post-metadata">

### Author: ![axelwang](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/a/6a8cbe/32.png) [@axelwang](https://discourse.paraview.org/u/axelwang)
#### Post date: [November 18, 2022, 4:12am UTC](https://discourse.paraview.org/t/how-to-add-a-reference-line-in-visualization/10781/3 "2022-11-18T04:12:49Z")

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Thank you so much @cory.quammen ! PyVista works very well!