# vtkAppendPolyData ?
**URL:** https://discourse.paraview.org/t/vtkappendpolydata/3766
**Category:** ParaView Support
**Created:** [March 6, 2020, 5:44pm UTC](https://discourse.paraview.org/t/vtkappendpolydata/3766 "2020-03-06T17:44:07Z")
**Posts on this page:** 9
**Page:** 1
### Author:  [@gujax](https://discourse.paraview.org/u/gujax)
#### Post date: [March 6, 2020, 5:44pm UTC](https://discourse.paraview.org/t/vtkappendpolydata/3766/1 "2020-03-06T17:44:07Z")
Hi
I am absolutely new to Paraview and only using its Qt-viewer. The solids are being generated by another application (GEANT4).
So I generated one cone and another hollow cone surrounding the first cone. When I form a union I should see a merged single cone.
However, when I try to open that wrl file, I get the following error.
The error is:
`vtkCompositeDataPipeline (0x61652d0): Input port 0 of algorithm vtkAppendPolyData(0x5064a70) has 0 connections but is not optional.`
I have no idea what to do. I Googled for solutions and looks like there are ways to figure this out using C++ scripts. But is there a way to resolve this on the Paraview viewer that I am using?
Another fact: when I do make a truncated cone, where it is truncated at the apex, then everything works. So looks like union at the apex is failing for whatever reasons.
Any help here is appreciated
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### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [March 9, 2020, 3:39am UTC](https://discourse.paraview.org/t/vtkappendpolydata/3766/2 "2020-03-09T03:39:31Z")
So the .wrl file is generated by GEANT4?
Can you share it here ?
Do you have other .wrl file that works ?
Here is one that do if that’s helps you.[bot2.wrl](https://discourse.paraview.org/uploads/short-url/r61e2KPgBMhHpqFFPSIYGFmGeO7.wrl) (50.7 KB)
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### Author:  [@gujax](https://discourse.paraview.org/u/gujax)
#### Post date: [March 9, 2020, 12:50pm UTC](https://discourse.paraview.org/t/vtkappendpolydata/3766/3 "2020-03-09T12:50:33Z")
Hello Mathieu
Here is a file that works:
[g4\_lens\_using\_pairofsolids\_to\_boolean.wrl](https://discourse.paraview.org/uploads/short-url/slopEjpEg6W109uKXQPqM6YF25V.wrl) (65.7 KB)
For example, part of this is a lens made using 2 pairs of hollow cones. Although the title says ‘boolean’, no booleans were created in this example purposely.
But I can create boolean of two solids pair wise it works and is similar to this solid i.e., boolean(solidA+solidB =E) and boolean(solidC+solidD=F) shows visually as G=[E;F] i.e., two separate booleans side-by-side.
Here is a file that does NOT work:
[g4\_unionofbooleans.wrl](https://discourse.paraview.org/uploads/short-url/6i8yfMN3F7dE9xPxLHdiUcnyFAa.wrl) (129 Bytes)
And this solid is like previous but is made using two pairs (A+B and C+D) to generate two booleans (A+B=E and C+D=F) and then union of these two booleans(E+F=G) to create a final boolean lens (G) very similar to the previous.
However, this one shows the error I mentioned and I do not see it on the Paraview veiwer.
Thanks for your help.
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### Author:  [@gujax](https://discourse.paraview.org/u/gujax)
#### Post date: [March 9, 2020, 12:56pm UTC](https://discourse.paraview.org/t/vtkappendpolydata/3766/4 "2020-03-09T12:56:05Z")
Hello Mathieu
Can you also explain what is bot2.wrl supposed to be and how it can help me?
Thank you
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### Author:  [@gujax](https://discourse.paraview.org/u/gujax)
#### Post date: [March 9, 2020, 8:23pm UTC](https://discourse.paraview.org/t/vtkappendpolydata/3766/5 "2020-03-09T20:23:41Z")
Hi Matheu
Yes I am able to visualize bot2.wrl but not sure what does that imply?
Thanks
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### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [March 10, 2020, 4:42am UTC](https://discourse.paraview.org/t/vtkappendpolydata/3766/6 "2020-03-10T04:42:17Z")
Just an example for a working file.
your non-working file is almost empty and does not contain a geometry :
```
#VRML V2.0 utf8
# Generated by VRML 2.0 driver of GEANT4
#---------- CAMERA
Viewpoint {
position 0 0 3936.73
}
#End of file.
```
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### Author:  [@gujax](https://discourse.paraview.org/u/gujax)
#### Post date: [March 10, 2020, 12:21pm UTC](https://discourse.paraview.org/t/vtkappendpolydata/3766/7 "2020-03-10T12:21:40Z")
Yes correct! Whenever I try to create solids which are boolean of two boolean solids I get nothing - an empty file.
No idea why? I will explore to see if its a problem with GAMOS or GEANT which generates the solid.
Thanks
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### Author:  [@gujax](https://discourse.paraview.org/u/gujax)
#### Post date: [March 10, 2020, 12:22pm UTC](https://discourse.paraview.org/t/vtkappendpolydata/3766/8 "2020-03-10T12:22:48Z")
BTW, in Paraview UI, is there a way to generate union of two solids. I could create two merged solids but I am not able to create an intersection solid or from them.
Thanks
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### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [March 11, 2020, 2:52am UTC](https://discourse.paraview.org/t/vtkappendpolydata/3766/9 "2020-03-11T02:52:37Z")
> [@gujax](#):
>
> No idea why?
A bug/missing feature in GEANT most likely.
> BTW, in Paraview UI, is there a way to generate union of two solids. I could create two merged solids but I am not able to create an intersection solid or from them.
There is a filter in VTK called vtkBooleanOperationPolyDataFilter, but it is not exposed in ParaView. You could write a simple XML plugin to expose it.