::New();
renderer1->SetLayer(1);
renderWindow->SetNumberOfLayers(2);
renderWindow->AddRenderer(renderer1);
```
the picker does not pick the rendered pixel position anymore.
To demonstrate the problem I made a simple demo [PickPosition.cxx](https://github.com/mat127/vtk-pick-position/blob/master/PickPosition.cxx). There are several spheres in the scene. Left mouse click invokes the `vtkWorldPointPicker` to get the position of pixel under the mouse cursor. Then a cross mark is placed at the picked position to visually verify it.
When lines 114-118 are commented out and there is just single renderer the picking works as expected - when mouse clicked over any sphere the cross mark is placed correctly at the sphere surface. But in case the second renderer is added (lines 114-118 are uncommented) picking always fails.
Am I using the picker correctly? Is it a bug?
Originally I used the `vtkPropPicker`, that uses the `vtkWorldPointPicker` internally to return the `PickPosition()`. I have found that the `vtkPropPicker` works fine even for more layered renderers in the 8.1.x versions but is not working for layered renderers in 8.2.0. Strange thing is that `vtkWorldPointPicker` does not work for layered renderers even in 8.1.x nor in 8.2.0.
To test the `vtkPropPicker` one can switch the the `style` type on the line 126.
Can someone help me please? How can I pick pixel position for multi layered renderers in the 8.2.0? Ideas, hints, explanations, … whatever.
Petr
---
### Author:  [@mat127](https://discourse.vtk.org/u/mat127)
#### Post date: [January 7, 2020, 3:12pm UTC](https://discourse.vtk.org/t/vtkworldpointpicker-seems-not-working-for-multi-layer-rendering/2322/2 "2020-01-07T15:12:44Z")
Let me share what I have found so far:
The cause of the problem is the fact that in case that 2 layered `vtkRenderer`s are used the call:
```
double z = renderer->GetZ(x,y);
```
returns always 1 regardless there is any prop at the given position in the Z-buffer or not (1 means there is no prop). Seems to me as a bug, or not?
`vtkWorldPointPicker::Pick(x,y,z,renderer)` uses this call in the implementation. `vtkPropPicker::Pick(x,y,z,renderer)` then uses the mentioned `vtkWorldPointPicker::Pick` internally so both pickers fail.
---
### Author:  [@mat127](https://discourse.vtk.org/u/mat127)
#### Post date: [January 8, 2020, 8:30am UTC](https://discourse.vtk.org/t/vtkworldpointpicker-seems-not-working-for-multi-layer-rendering/2322/3 "2020-01-08T08:30:06Z")
For those interested in a workaround:
Use directly the `vtkRenderer::PickProp()` and then extract the Z display coordinate by the `vtkRenderer::GetZ()`
```
if(renderer->PickProp(clickPos[0], clickPos[1]) == nullptr)
return nullptr;
double display[3];
display[0] = clickPos[0];
display[1] = clickPos[1];
display[2] = renderer->GetPickedZ();
```
Finally convert the display coordinates to world:
```
renderer->SetDisplayPoint (display);
renderer->DisplayToWorld ();
double * world = renderer->GetWorldPoint ();
double * picked = new double[3];
for (int i=0; i < 3; i++) {
picked[i] = world[i] / world[3];
}
```
But note that this works only with the current vtk master branch. To make it work with the 8.2.0 release one has to apply the [!6009](https://gitlab.kitware.com/vtk/vtk/merge_requests/6009) merge request. For complete working solution see the updated [PickPosition.cxx](https://github.com/mat127/vtk-pick-position/blob/3a90698ebcc340e84ab20f2522852a856aba61e9/PickPosition.cxx).
---
### Author:  [@mat127](https://discourse.vtk.org/u/mat127)
#### Post date: [January 8, 2020, 8:36am UTC](https://discourse.vtk.org/t/vtkworldpointpicker-seems-not-working-for-multi-layer-rendering/2322/4 "2020-01-08T08:36:53Z")
Please note that the source code line numbers mentioned in the initial post are valid just in [this version of the PickPosition.cxx](https://github.com/mat127/vtk-pick-position/blob/2714e8384e3214357a69f6b34b83d999685a2fd5/PickPosition.cxx)
---
### Author:  [@reload0236](https://discourse.vtk.org/u/reload0236)
#### Post date: [January 19, 2024, 2:27pm UTC](https://discourse.vtk.org/t/vtkworldpointpicker-seems-not-working-for-multi-layer-rendering/2322/5 "2024-01-19T14:27:49Z")
See here:
[vtkPropPicker in VTK 9.1 is now returning wrong world coordinates. - Development - VTK](https://discourse.vtk.org/t/vtkproppicker-in-vtk-9-1-is-now-returning-wrong-world-coordinates/8061/40)