# vtkCellPicker can not pick vtk.vtkActor
**URL:** https://discourse.vtk.org/t/vtkcellpicker-can-not-pick-vtk-vtkactor/7114
**Category:** Support
**Created:** [November 9, 2021, 6:00am UTC](https://discourse.vtk.org/t/vtkcellpicker-can-not-pick-vtk-vtkactor/7114 "2021-11-09T06:00:51Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@zhang-qiang-github](https://discourse.vtk.org/u/zhang-qiang-github)
#### Post date: [November 9, 2021, 6:00am UTC](https://discourse.vtk.org/t/vtkcellpicker-can-not-pick-vtk-vtkactor/7114/1 "2021-11-09T06:00:51Z")
There is `vtk.vtkImageActor` and `vtk.vtkActor` in the `vtkRenderer`. I want to pick the actor in the mouse move event with `vtkCellPicker`. I can pick `vtkImageActor`, but it is failed to pick `vtkActor`. The completed code is:
```auto
import vtk
from vtk.util.numpy_support import vtk_to_numpy, numpy_to_vtk
import numpy as np
def numpyToVTK(data):
if len(data.shape) == 2:
data = data[:, :, np.newaxis]
flat_data_array = data.transpose(2,1,0).flatten()
vtk_data = numpy_to_vtk(num_array=flat_data_array, deep=True, array_type=vtk.VTK_FLOAT)
shape = data.shape
img = vtk.vtkImageData()
img.GetPointData().SetScalars(vtk_data)
img.SetDimensions(shape[0], shape[1], shape[2])
return img
img = np.zeros(shape=[512, 512])
img[0:256, 0:256] = 0
img[0:256, 256:] = 64
img[256:, 0:256] = 128
img[256:, 256:] = 255
img = numpyToVTK(img)
imgActor = vtk.vtkImageActor()
imgActor.SetInputData(img)
lineSource = vtk.vtkLineSource()
lineSource.SetPoint1(0, 0, 0)
lineSource.SetPoint2(512, 512, 0)
lineSource.Update()
lineMapper = vtk.vtkPolyDataMapper()
lineMapper.SetInputData(lineSource.GetOutput())
lineActor = vtk.vtkActor()
lineActor.SetMapper(lineMapper)
lineActor.GetProperty().SetColor(255, 0, 0)
lineActor.GetProperty().SetLineWidth(5)
# lineActor.GetProperty().EdgeVisibilityOn() ############################ it make difference
renderer = vtk.vtkRenderer()
renderer.AddActor(imgActor)
renderer.AddActor(lineActor)
renderer.SetBackground(0.4, 0.5, 0.6)
renderWindow = vtk.vtkRenderWindow()
renderWindow.AddRenderer(renderer)
renderWindow.Render()
def mousemove(iren, even):
pos = iren.GetEventPosition()
picker = vtk.vtkCellPicker()
picker.Pick(pos[0], pos[1], 0, renderer)
actor = picker.GetProp3D()
# print(pos)
if isinstance(actor, vtk.vtkImageActor):
print('Picture actor')
elif isinstance(actor, vtk.vtkActor):
print("line actor")
else:
print('none actor')
renderWindowInteractor = vtk.vtkRenderWindowInteractor()
renderWindowInteractor.AddObserver("MouseMoveEvent", mousemove)
style = vtk.vtkInteractorStyleImage()
renderWindowInteractor.SetInteractorStyle(style)
renderWindowInteractor.SetRenderWindow(renderWindow)
renderWindowInteractor.Initialize()
renderWindowInteractor.Start()
```
In thte `mousemove` function, I print the picked actor. But it only print `Picture actor`. Is there anything wrong with `vtkCellPicker`?
```auto
def mousemove(iren, even):
pos = iren.GetEventPosition()
picker = vtk.vtkCellPicker()
picker.Pick(pos[0], pos[1], 0, renderer)
actor = picker.GetProp3D()
# print(pos)
if isinstance(actor, vtk.vtkImageActor):
print('Picture actor')
elif isinstance(actor, vtk.vtkActor):
print("line actor")
else:
print('none actor')
```
---
### Author:  [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [November 10, 2021, 11:46am UTC](https://discourse.vtk.org/t/vtkcellpicker-can-not-pick-vtk-vtkactor/7114/2 "2021-11-10T11:46:58Z")
Hello, Zhang,
I guess you need a `vtkPropPicker` instead: [https://vtk.org/doc/nightly/html/classvtkPropPicker.html](https://vtk.org/doc/nightly/html/classvtkPropPicker.html).
regards,
Paulo
---
### Author:  [@zhang-qiang-github](https://discourse.vtk.org/u/zhang-qiang-github)
#### Post date: [November 10, 2021, 12:58pm UTC](https://discourse.vtk.org/t/vtkcellpicker-can-not-pick-vtk-vtkactor/7114/3 "2021-11-10T12:58:13Z")
@Paulo_Carvalho , Thank you very much for the suggestion, and `vtkPropPicker` works.
But, why `vtkCellPicker.GetProp3D` do not return the correct result? If `vtkCellPicker.GetProp3D` do not return the picked prop, what is the output of `vtkCellPicker.GetProp3D`?
---
### Author:  [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [November 10, 2021, 1:35pm UTC](https://discourse.vtk.org/t/vtkcellpicker-can-not-pick-vtk-vtkactor/7114/4 "2021-11-10T13:35:35Z")
From here: [VTK: vtkCellPicker Class Reference](https://vtk.org/doc/nightly/html/classvtkCellPicker.html#a0e8450adaa27fb1c597f6a28779a4bfc)
> If it is On, then the clipping planes become pickable objects, even though they are usually invisible. This means that if the pick ray intersects a clipping plane before it hits anything else, the pick will stop at that clipping plane. The [GetProp3D()](https://vtk.org/doc/nightly/html/classvtkAbstractPropPicker.html#a0ef70cafcefff099052ea0591ce6514d) and [GetMapper()](https://vtk.org/doc/nightly/html/classvtkPicker.html#a7071c55031aa74e4ec9ae2f4f1c1fca6) methods **will return the Prop3D and Mapper that the clipping plane belongs to**. The [GetClippingPlaneId()](https://vtk.org/doc/nightly/html/classvtkCellPicker.html#a4edfefba91bdd9925177dc37f528f2ff) method will return the index of the clipping plane so that you can retrieve it from the mapper, or -1 if no clipping plane was picked.
(emphasis added)
This implies that no actor will be returned if there are no clipping planes.
---
### Author:  [@zhang-qiang-github](https://discourse.vtk.org/u/zhang-qiang-github)
#### Post date: [November 12, 2021, 1:52pm UTC](https://discourse.vtk.org/t/vtkcellpicker-can-not-pick-vtk-vtkactor/7114/5 "2021-11-12T13:52:06Z")
In my understanding, it means:
```auto
if PickClippingPlanes = True
if there are clipping planes
the pick ray will stop at the clipping plane (belong to a prop) , and vtkCellPicker would return this prop
if there is no clipping planes
the pick ray will stop at a prop, and vtkCellPicker would return this prop
if PickClippingPlanes = False
the pick ray will stop at a prop, and vtkCellPicker would return this prop
```
In the source code of `vtkCellPicker` (Line 287~310):
```auto
double tMin = VTK_DOUBLE_MAX;
double t1 = 0.0;
double t2 = 1.0;
// Clip the ray with the mapper's ClippingPlanes and adjust t1, t2.
// This limits the pick search to the inside of the clipped region.
int clippingPlaneId = -1;
if (m &&
!this->ClipLineWithPlanes(m, this->Transform->GetMatrix(), p1, p2, t1, t2, clippingPlaneId))
{
return VTK_DOUBLE_MAX;
}
// Initialize the pick position to the frontmost clipping plane
if (this->PickClippingPlanes && clippingPlaneId >= 0)
{
tMin = t1;
}
// HyperTreeGrid
else if ((htgMapper = vtkAbstractHyperTreeGridMapper::SafeDownCast(m)))
{
tMin = this->IntersectHyperTreeGridWithLine(p1, p2, t1, t2, htgMapper);
}
...
```
**Code 1**. The following code only calculate the position of ClippingPlanes.
```auto
if (m &&
!this->ClipLineWithPlanes(m, this->Transform->GetMatrix(), p1, p2, t1, t2, clippingPlaneId))
{
return VTK_DOUBLE_MAX;
}
```
**Code 2**. The following code only initialize the pick position.
```auto
// Initialize the pick position to the frontmost clipping plane
if (this->PickClippingPlanes && clippingPlaneId >= 0)
{
tMin = t1;
}
```
If there is no clipping planes, `this->ClipLineWithPlanes` would return 1, then `Code 2` is executed.
In `Code 2`:
```auto
if this->PickClippingPlanes = False, the code would be continue executed.
if this->PickClippingPlanes = True, only tMin is updated and the code would be continue executed.
```
Thus, I think that no clipping plane may not result in the wrong result of `vtkCellPicker`. Is that correct?
Moreover, if I want to use `vtkCellPicker` to pick correct actor (because I want to use the `SetTolerance` method), how should I modify my code? I use `PickClippingPlanesOff` or `PickClippingPlanesOn` in my code, but it don’t make any change:
```auto
def mousemove(iren, even):
pos = iren.GetEventPosition()
picker = vtk.vtkCellPicker()
picker.PickClippingPlanesOff() ################################### change
picker.Pick(pos[0], pos[1], 0, renderer)
actor = picker.GetProp3D()
# print(pos)
if isinstance(actor, vtk.vtkImageActor):
print('Picture actor')
elif isinstance(actor, vtk.vtkActor):
print("line actor")
else:
print('none actor')
```
Any suggestion is appreciated~~~
---
### Author:  [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [November 12, 2021, 2:36pm UTC](https://discourse.vtk.org/t/vtkcellpicker-can-not-pick-vtk-vtkactor/7114/6 "2021-11-12T14:36:36Z")
Hello,
I think your question has already been answered. Please, mark the answer as solution so others can benefit from it. If you have further questions, please, start new ones.
thanks,
Paulo
---
### Author:  [@zhang-qiang-github](https://discourse.vtk.org/u/zhang-qiang-github)
#### Post date: [November 12, 2021, 3:19pm UTC](https://discourse.vtk.org/t/vtkcellpicker-can-not-pick-vtk-vtkactor/7114/7 "2021-11-12T15:19:34Z")
Actually, my question is “vtkCellPicker can not pick vtk.vtkActor”. Even `vtkPropPicker` solve my problem, I still feel confuzed why vtkCellPicker can not correctly pick vtk.vtkActor.