### Author:  [@yen](https://discourse.vtk.org/u/yen)
#### Post date: [June 15, 2023, 6:39am UTC](https://discourse.vtk.org/t/how-can-i-combine-a-series-of-polydata-to-a-3d-object-in-c/11726/1 "2023-06-15T06:39:32Z")
Hello, I am a newcomer to VTK recently. Now I have a task to finish. I need to construct a 3D object from a several sections of an object. To be more specifically, I need to first construct a section from multiple points and then stack all scetions into a 3D object.
Here is my current thought and code. I combine points in a single section and store them in vtkpolyData. Later I want to stack all vtkpolyData and then show them in the vtk renderer windows.
dsg\_ch0 is the section variable, whose structure is vector\, Distance contains x, y, z coordination.
Does anyone know how to solve this problem properly? Thank you
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### Author:  [@sankhesh](https://discourse.vtk.org/u/sankhesh)
#### Post date: [June 15, 2023, 2:10pm UTC](https://discourse.vtk.org/t/how-can-i-combine-a-series-of-polydata-to-a-3d-object-in-c/11726/2 "2023-06-15T14:10:08Z")
If you need the ability to access properties, pick each individual polydata, you can use the `vtkCompositeDataSet` / `vtkPartitionedDataSetCollection` API for managing the whole model.
If you would simply like to combine them into a single vtkPolyData object, use `vtkAppendPolyData`.
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### Author:  [@yen](https://discourse.vtk.org/u/yen)
#### Post date: [June 16, 2023, 12:09am UTC](https://discourse.vtk.org/t/how-can-i-combine-a-series-of-polydata-to-a-3d-object-in-c/11726/3 "2023-06-16T00:09:56Z")
Thank you sir! I actually tried vtkAppendPolyData before. However, it seemed to not work with vtkNew.
Here is my code using vtkAppendPolyData:
And here is the result I got:
I am quite confused what happended. If I use vtkNew to replace all the pointer, it still not work.
When I did not use vtkAppendPolyData, it will work well to show me the polynomial line. Do you know what’s going on?
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### Author:  [@amaclean](https://discourse.vtk.org/u/amaclean)
#### Post date: [June 16, 2023, 4:19am UTC](https://discourse.vtk.org/t/how-can-i-combine-a-series-of-polydata-to-a-3d-object-in-c/11726/4 "2023-06-16T04:19:25Z")
I think it is your use of **Get** here: `appendFilter->AddInputData(polyData.Get());` , `polyData.Get())` is returning a raw pointer to the contained object. In this case it goes out of scope after the for loop exits, hence no PolyData.
Don’t use **Get** and see what happens. Also look at [CombinePolyData](https://examples.vtk.org/site/Cxx/Filtering/CombinePolyData/).
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### Author:  [@yen](https://discourse.vtk.org/u/yen)
#### Post date: [June 16, 2023, 6:11am UTC](https://discourse.vtk.org/t/how-can-i-combine-a-series-of-polydata-to-a-3d-object-in-c/11726/5 "2023-06-16T06:11:42Z")
I change to this, but it still not work.
But since you mentioned raw pointer. I come out that I first store all polydata I get in my own class. And then I use appendpolydata to store the polydata I store in the class.
BTW, I want to ask does this issue relative to the difference between vtkNew and vtkSmartPointer?
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### Author:  [@sankhesh](https://discourse.vtk.org/u/sankhesh)
#### Post date: [June 16, 2023, 2:16pm UTC](https://discourse.vtk.org/t/how-can-i-combine-a-series-of-polydata-to-a-3d-object-in-c/11726/6 "2023-06-16T14:16:27Z")
@yen I think the issue is that your polydata doesn’t have any cells. You are using `InsertCellPoint` without calling `InsertNextCell`. You need both of those calls for adding a valid cell to the lines cellarray.
Something like:
```cpp
lines->InsertNextCell(dsb_cho[i].size());
for(...)
{
points->InsertNextPoint(...)
lines->InsertCellPoint(j)
}
```
---
### Author:  [@yen](https://discourse.vtk.org/u/yen)
#### Post date: [June 16, 2023, 11:59pm UTC](https://discourse.vtk.org/t/how-can-i-combine-a-series-of-polydata-to-a-3d-object-in-c/11726/8 "2023-06-16T23:59:44Z")
Thank you very much, I indeed miss InsertNextCell. Thank you very much, now I can continue my work!