# Get single contour from vtkPolyData

**URL:** https://discourse.vtk.org/t/get-single-contour-from-vtkpolydata/10536
**Category:** Support
**Created:** [January 25, 2023, 1:43pm UTC](https://discourse.vtk.org/t/get-single-contour-from-vtkpolydata/10536 "2023-01-25T13:43:32Z")
**Posts on this page:** 1
**Showing post:** 4

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### Author: ![SebastianWilke](https://discourse.vtk.org/user_avatar/discourse.vtk.org/sebastianwilke/32/6441_2.png) [@SebastianWilke](https://discourse.vtk.org/u/SebastianWilke)
#### Post date: [February 1, 2023, 1:03am UTC](https://discourse.vtk.org/t/get-single-contour-from-vtkpolydata/10536/4 "2023-02-01T01:03:16Z")

</div>

Thank you for your ongoing help! I understood and followed your suggestion.

I subclassed `vtkCallbackCommand`. Inside its overridden `Execute()`-function I got this far:

```auto
void HPvtkRenderCallback::Execute(
    vtkObject* caller, unsigned long eventId, void* callData
)
{
	std::cout << "Render callback" << std::endl;
	std::cout << "Event: " << vtkCommand::GetStringFromEventId(eventId) << '\n';
	auto* renderer = static_cast<vtkRenderer*>(caller);
	double d1 = renderer->GetClippingRangeExpansion();
	double d2 = renderer->GetClippingRangeExpansionMinValue();
	double d3 = renderer->GetClippingRangeExpansionMaxValue();
	vtkActorCollection* propCollection = renderer->GetActors();
	propCollection->InitTraversal();
	for (vtkIdType i = 0; i < propCollection->GetNumberOfItems(); ++i)
	{
		vtkActor* actor = propCollection->GetNextActor();
	}
}

```

The calIback generally works. However, now I’m having problems getting the correct actor.  
With this actor, I planned on:

1. getting the actors mapper
2. getting both mappers clipping planes (front and back as you said)
3. calling `vtkPlane::Push(double distance)` with either `d1`, `d2` or `d3` (not figured out yet)

I am using VTK-9.0, so [`SetObjectName()/GetObjectName()`](https://discourse.vtk.org/t/naming-vtkactors/9958/3) is not an option.

How do I distinguish the correct actor from others?

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_[View the full topic](https://discourse.vtk.org/t/get-single-contour-from-vtkpolydata/10536)._