# How to pick a point closest from the mouse cursor?
**URL:** https://discourse.vtk.org/t/how-to-pick-a-point-closest-from-the-mouse-cursor/4318
**Category:** Support
**Created:** [September 29, 2020, 2:59am UTC](https://discourse.vtk.org/t/how-to-pick-a-point-closest-from-the-mouse-cursor/4318 "2020-09-29T02:59:26Z")
**Posts on this page:** 11
**Page:** 1
### Author:  [@Kim\_William](https://discourse.vtk.org/u/Kim_William)
#### Post date: [September 29, 2020, 2:59am UTC](https://discourse.vtk.org/t/how-to-pick-a-point-closest-from-the-mouse-cursor/4318/1 "2020-09-29T02:59:26Z")
Hi all.
I have a question about pick a point.
I have a commercial program that provides a function what if the mouse cursor moving, the closest point is selected.
It is useful when I zoom in the point cloud data and check the coordinate.
I made a sample program that checking the coordinate along with the mouse cursor.
I referred to the below link.
[https://lorensen.github.io/VTKExamples/site/Cxx/Interaction/PointPicker/](https://lorensen.github.io/VTKExamples/site/Cxx/Interaction/PointPicker/)
I only can get the point’s coordinate when the cursor is above the point.
Does the VTK library provide the selecting the closest point from the mouse cursor?
I need your advise.
Thank you 🙂
---
### Author:  [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [September 29, 2020, 5:13pm UTC](https://discourse.vtk.org/t/how-to-pick-a-point-closest-from-the-mouse-cursor/4318/2 "2020-09-29T17:13:55Z")
Hi, Kim,
I suggest you to take a look at [https://vtk.org/doc/nightly/html/classvtkPointLocator.html](https://vtk.org/doc/nightly/html/classvtkPointLocator.html) and [https://vtk.org/doc/nightly/html/classvtkCellLocator.html](https://vtk.org/doc/nightly/html/classvtkCellLocator.html) . Both have methods called `FindClosestPoint*()` and `FindClosestCell*()`. One should suit you.
regards,
Paulo
---
### Author:  [@Kim\_William](https://discourse.vtk.org/u/Kim_William)
#### Post date: [October 5, 2020, 12:36am UTC](https://discourse.vtk.org/t/how-to-pick-a-point-closest-from-the-mouse-cursor/4318/3 "2020-10-05T00:36:30Z")
Hi, Paulo.
Thank you for your help.
But I have an additional question…
Do I need a preparation step to use the vtkPointLocator?
I have written the code that picking a point from the GetEventPosition() function on OnMouseMove() event.
I referred to the following examples:
[https://lorensen.github.io/VTKExamples/site/Cxx/Interaction/Picking/](https://lorensen.github.io/VTKExamples/site/Cxx/Interaction/Picking/)
[https://lorensen.github.io/VTKExamples/site/Cxx/Interaction/PointPicker/](https://lorensen.github.io/VTKExamples/site/Cxx/Interaction/PointPicker/)
I added the vtkPointLocator and call the FindClosestPoint() function, but it always returns -1.
I referred to the following examples:
[https://lorensen.github.io/VTKExamples/site/Cxx/PolyData/PointLocator/](https://lorensen.github.io/VTKExamples/site/Cxx/PolyData/PointLocator/)
[https://lorensen.github.io/VTKExamples/site/Cxx/PolyData/PointLocatorVisualization/](https://lorensen.github.io/VTKExamples/site/Cxx/PolyData/PointLocatorVisualization/)
Could you please advise for me?
Thank you.
Best regards,
William Kim
---
### Author:  [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [October 8, 2020, 6:12pm UTC](https://discourse.vtk.org/t/how-to-pick-a-point-closest-from-the-mouse-cursor/4318/4 "2020-10-08T18:12:49Z")
Hello, can you post the part of your code involved in point search?
regards,
Paulo
---
### Author:  [@Kim\_William](https://discourse.vtk.org/u/Kim_William)
#### Post date: [October 12, 2020, 12:09am UTC](https://discourse.vtk.org/t/how-to-pick-a-point-closest-from-the-mouse-cursor/4318/5 "2020-10-12T00:09:39Z")
Hi Paulo.
I have modified my code and it doesn’t return -1 but it doesn’t work well.
I attached the code part of the mouse event, if you can review my code I can send you my full code.
```
virtual void OnMouseMove() override
{
if (m_bEnablePicking == true)
{
int* pos = this->GetInteractor()->GetEventPosition();
vtkNew picker;
picker->Pick(pos[0], pos[1], 0, this->GetDefaultRenderer());
double* worldPosition = picker->GetPickPosition();
int id = locator_point->FindClosestPoint(pos[0], pos[1], pos[2]);
double* position = polydata->GetPoint(id);
}
vtkInteractorStyleTrackballCamera::OnMouseMove();
}
vtkSmartPointer locator_point;
```
Thank you.
Best regards,
William Kim
---
### Author:  [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [October 12, 2020, 2:29pm UTC](https://discourse.vtk.org/t/how-to-pick-a-point-closest-from-the-mouse-cursor/4318/6 "2020-10-12T14:29:09Z")
Hello, Kim,
Try changing your pick handling code to something like this (notice the `vtkPointPicker` in place of `vtkPropPicker`):
```cpp
// Get pick position in 2D screen coordinates.
int* clickPos = this->GetInteractor()->GetEventPosition();
// Get the point of a 3D object under the 2D screen coordinates (ray casting).
vtkSmartPointer pointPicker = vtkSmartPointer::New();
pointPicker->Pick(clickPos[0], clickPos[1], 0, this->GetDefaultRenderer());
//if a point was picked...
if( pointPicker->GetPointId() != -1 ) {
// ...get the picked location in world coordinates.
double* pos = picker->GetPickPosition();
// Get the picked vertex.
int id = locator_point->FindClosestPoint(pos[0], pos[1], pos[2]);
double* position = polydata->GetPoint(id);
(...)
} else {
std::cout << "Pick failed." << std::endl;
}
```
I hope this helps,
Paulo
---
### Author:  [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [October 12, 2020, 2:35pm UTC](https://discourse.vtk.org/t/how-to-pick-a-point-closest-from-the-mouse-cursor/4318/7 "2020-10-12T14:35:02Z")
Taking a second look, I think you can stick with the `vtkPropPicker`. So, can you paste the part of the code where you instantiate and configure `locator_point`?
---
### Author:  [@Kim\_William](https://discourse.vtk.org/u/Kim_William)
#### Post date: [October 13, 2020, 12:00am UTC](https://discourse.vtk.org/t/how-to-pick-a-point-closest-from-the-mouse-cursor/4318/8 "2020-10-13T00:00:14Z")
Hi Paulo.
I attached my code as below:
```
vtkNew m_vtkPCDPoints;
vtkNew m_vtkPolydata;
vtkNew colors;
//...
m_vtkPolydata->SetPoints(m_vtkPCDPoints);
m_vtkPolydata->GetPointData()->SetScalars(colors);
m_vtkPointLocator->SetDataSet(m_vtkPolydata);
//...
```
Thank you.
---
### Author:  [@Kim\_William](https://discourse.vtk.org/u/Kim_William)
#### Post date: [October 13, 2020, 12:10am UTC](https://discourse.vtk.org/t/how-to-pick-a-point-closest-from-the-mouse-cursor/4318/9 "2020-10-13T00:10:18Z")
Hi Paulo.
oh… The vtkPointPicker works better than vtkPropPicker.
I think it is fine. Thank you.
May I ask you to review my code that written above comment?
---
### Author:  [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [October 13, 2020, 1:17pm UTC](https://discourse.vtk.org/t/how-to-pick-a-point-closest-from-the-mouse-cursor/4318/10 "2020-10-13T13:17:22Z")
Hi, Kim,
Do `polydata` and `m_vtkPolydata` in your examples point to the same object? If not, you can’t use point IDs of one object to fetch points of another data set. The IDs are like indexes in a container.
all the best,
Paulo
---
### Author:  [@Kim\_William](https://discourse.vtk.org/u/Kim_William)
#### Post date: [October 14, 2020, 5:15am UTC](https://discourse.vtk.org/t/how-to-pick-a-point-closest-from-the-mouse-cursor/4318/11 "2020-10-14T05:15:25Z")
Hi Paulo.
Thank you for your kindly help.
I solved my issue by your advise.
Thank you 🙂
Best regards,
William Kim