# Changing the geometry of an actor made the picker worked incorrectly
**URL:** https://discourse.vtk.org/t/changing-the-geometry-of-an-actor-made-the-picker-worked-incorrectly/2030
**Category:** Support
**Created:** [November 3, 2019, 9:06am UTC](https://discourse.vtk.org/t/changing-the-geometry-of-an-actor-made-the-picker-worked-incorrectly/2030 "2019-11-03T09:06:04Z")
**Posts on this page:** 9
**Page:** 1
### Author:  [@tdchen](https://discourse.vtk.org/u/tdchen)
#### Post date: [November 3, 2019, 9:06am UTC](https://discourse.vtk.org/t/changing-the-geometry-of-an-actor-made-the-picker-worked-incorrectly/2030/1 "2019-11-03T09:06:04Z")
After an actor were created, its geometry were changed.
In fact I just changed its polydata by splitting 1 big triangle into 3.
But I found when I picked the actor, the big triangle seemed become 1 small triangle and the other 2 small ones can’t be hitted, they became hollow!!
But the actor was displayed correctly.
That made me puzzle and I need you help.
Thank you.
---
### Author:  [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [November 4, 2019, 1:52pm UTC](https://discourse.vtk.org/t/changing-the-geometry-of-an-actor-made-the-picker-worked-incorrectly/2030/2 "2019-11-04T13:52:15Z")
What VTK version are you using?
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### Author:  [@tdchen](https://discourse.vtk.org/u/tdchen)
#### Post date: [November 4, 2019, 2:15pm UTC](https://discourse.vtk.org/t/changing-the-geometry-of-an-actor-made-the-picker-worked-incorrectly/2030/3 "2019-11-04T14:15:47Z")
vtk7.1.1
Perhaps, I need to tell the render that I had changed one actor.
But I don’t know how to do it.
---
### Author:  [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [November 4, 2019, 4:05pm UTC](https://discourse.vtk.org/t/changing-the-geometry-of-an-actor-made-the-picker-worked-incorrectly/2030/4 "2019-11-04T16:05:58Z")
Perhaps you could try something like this:
```
unstructuredGrid->GetCellData()->Modified();
```
The method above supposedly notifies other algorithms of changes in geometry. That potentially includes the spatial index used by VTK to enable picking.
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### Author:  [@tdchen](https://discourse.vtk.org/u/tdchen)
#### Post date: [November 6, 2019, 2:39am UTC](https://discourse.vtk.org/t/changing-the-geometry-of-an-actor-made-the-picker-worked-incorrectly/2030/5 "2019-11-06T02:39:03Z")
I have done that, and the actor is displayed correctly.
The problem is only for the picker.
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### Author:  [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [December 17, 2019, 11:58pm UTC](https://discourse.vtk.org/t/changing-the-geometry-of-an-actor-made-the-picker-worked-incorrectly/2030/6 "2019-12-17T23:58:47Z")
Sorry for the late reply. Is it possible/viable to upgrade to latest version?
---
### Author:  [@tdchen](https://discourse.vtk.org/u/tdchen)
#### Post date: [December 18, 2019, 2:39am UTC](https://discourse.vtk.org/t/changing-the-geometry-of-an-actor-made-the-picker-worked-incorrectly/2030/7 "2019-12-18T02:39:10Z")
I have tried it in vtk8.2. It still doesn’t work.
In fact, someone have told me to call the vtkPolyData::BuildCells(), and it does works in a simple test program.
But in a more complicated program, it still failed.
That make me confused.
---
### Author:  [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [December 18, 2019, 11:17am UTC](https://discourse.vtk.org/t/changing-the-geometry-of-an-actor-made-the-picker-worked-incorrectly/2030/8 "2019-12-18T11:17:02Z")
Just checking: do you call that method on ALL instances? I mean, maybe you used some filter that spawned more `vtkPolyData`s that your code currently manages.
As you said the call works with simple examples, another approach is to tear down scene complexity until you obtain a working version of your code. That’s what I do when I face mysterious problems like that. I comment out most of the code and uncomment them bit-by-bit until I the issue kicks in.
---
### Author:  [@tdchen](https://discourse.vtk.org/u/tdchen)
#### Post date: [September 15, 2021, 11:07pm UTC](https://discourse.vtk.org/t/changing-the-geometry-of-an-actor-made-the-picker-worked-incorrectly/2030/9 "2021-09-15T23:07:43Z")
good idea. Carvalho. I’ll try.
sorry for my so late reply.