# A question about vtkStructuredGrid
**URL:** https://discourse.vtk.org/t/a-question-about-vtkstructuredgrid/7318
**Category:** Support
**Tags:** jobs
**Created:** [December 3, 2021, 3:57am UTC](https://discourse.vtk.org/t/a-question-about-vtkstructuredgrid/7318 "2021-12-03T03:57:32Z")
**Posts on this page:** 12
**Page:** 1
### Author:  [@KeyboardMan](https://discourse.vtk.org/u/KeyboardMan)
#### Post date: [December 3, 2021, 3:57am UTC](https://discourse.vtk.org/t/a-question-about-vtkstructuredgrid/7318/1 "2021-12-03T03:57:33Z")
I try to use vtkStructuredGrid to draw the grid in the polar coordinate system。But the hexahedral cell in vtkCellType is not fan-shaped。
I found this when I was looking for information（like c）, but it didn’t explain how to achieve it, so I want to ask.
I want to achieve this effect [https://kitware.github.io/vtk-examples/site/Cxx/VisualizationAlgorithms/LOxGrid/](https://kitware.github.io/vtk-examples/site/Cxx/VisualizationAlgorithms/LOxGrid/)
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### Author:  [@mwestphal](https://discourse.vtk.org/u/mwestphal)
#### Post date: [December 3, 2021, 1:11pm UTC](https://discourse.vtk.org/t/a-question-about-vtkstructuredgrid/7318/2 "2021-12-03T13:11:32Z")
> [@KeyboardMan](#):
>
> But the hexahedral cell in vtkCellType is not fan-shaped。
What do you mean fan-shaped ? The cell will juste be linking the point you positioned yourself.
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### Author:  [@Yohann\_Bearzi](https://discourse.vtk.org/u/Yohann_Bearzi)
#### Post date: [December 3, 2021, 1:20pm UTC](https://discourse.vtk.org/t/a-question-about-vtkstructuredgrid/7318/3 "2021-12-03T13:20:08Z")
I think that what @KeyboardMan would like to achieve would be to have curved hexahedra in his polar grid so that the grid is angularly smooth. Unfortunately, as of today, cells inside a `vtkStructuredGrid` are linear.
EDIT: The illustration for `vtkStructuredGrid` is kind of deceptive… Sorry it lead to a confusion.
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### Author:  [@Yohann\_Bearzi](https://discourse.vtk.org/u/Yohann_Bearzi)
#### Post date: [December 3, 2021, 1:26pm UTC](https://discourse.vtk.org/t/a-question-about-vtkstructuredgrid/7318/4 "2021-12-03T13:26:54Z")
You could get this kind of smooth result if you used non linear cells in a `vtkUnstructuredGrid`. You might have to create a custom class so you can automatize indexing (your class could inherit from `vtkUnstructuredGrid` and add relevant methods). Look at `vtkHigherOrderHexahedron` and related cells. There are a handful to choose from.
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### Author:  [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [December 3, 2021, 8:46pm UTC](https://discourse.vtk.org/t/a-question-about-vtkstructuredgrid/7318/5 "2021-12-03T20:46:37Z")
Like @Yohann_Bearzi, I’d also go for `vtkUnstructuredGrid`. That’s the class I use to model grids with cells of arbitrary shapes like those we need for geology applications:
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### Author:  [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [December 3, 2021, 9:00pm UTC](https://discourse.vtk.org/t/a-question-about-vtkstructuredgrid/7318/6 "2021-12-03T21:00:23Z")
If you want an specific “fan shaped” grid, you might be interested in looking at this example: [https://kitware.github.io/vtk-examples/site/Cxx/StructuredGrid/SGrid/](https://kitware.github.io/vtk-examples/site/Cxx/StructuredGrid/SGrid/)
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### Author:  [@KeyboardMan](https://discourse.vtk.org/u/KeyboardMan)
#### Post date: [December 4, 2021, 1:57am UTC](https://discourse.vtk.org/t/a-question-about-vtkstructuredgrid/7318/7 "2021-12-04T01:57:59Z")
I think this is not what I need, what I need is grid drawing in polar coordinate system
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### Author:  [@KeyboardMan](https://discourse.vtk.org/u/KeyboardMan)
#### Post date: [December 4, 2021, 2:05am UTC](https://discourse.vtk.org/t/a-question-about-vtkstructuredgrid/7318/8 "2021-12-04T02:05:57Z")
Processing: Screenshot\_2021-12-04-10-04-04-779\_com.miui.notes.jpg…
like this
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### Author:  [@KeyboardMan](https://discourse.vtk.org/u/KeyboardMan)
#### Post date: [December 4, 2021, 2:17am UTC](https://discourse.vtk.org/t/a-question-about-vtkstructuredgrid/7318/9 "2021-12-04T02:17:50Z")
That’s the case, so I can only make as many grids as possible in the theta direction to get an approximate effect?
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### Author:  [@KeyboardMan](https://discourse.vtk.org/u/KeyboardMan)
#### Post date: [December 4, 2021, 2:29am UTC](https://discourse.vtk.org/t/a-question-about-vtkstructuredgrid/7318/10 "2021-12-04T02:29:04Z")
You can really try this, and try again on weekdays. thank you very much
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### Author:  [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [December 4, 2021, 2:33pm UTC](https://discourse.vtk.org/t/a-question-about-vtkstructuredgrid/7318/11 "2021-12-04T14:33:16Z")
My point is that you need to express each cell geometry explicitly with `vtkUnstructuredGrid`. VTK doesn’t have a “`vtkPolarGrid`”. Either this or elaborate over the example I posted further above that uses `vtkStructuredGrid`.
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### Author:  [@lassoan](https://discourse.vtk.org/u/lassoan)
#### Post date: [December 6, 2021, 6:00pm UTC](https://discourse.vtk.org/t/a-question-about-vtkstructuredgrid/7318/12 "2021-12-06T18:00:18Z")
We use a grid transform and a transform filter to warp VTK objects stored in polar coordinates to Cartesian coordinate system. It works on polydata, unstructured grid, etc. directly. For images, we use the same transform with a vtkImageResample filter.