vtkCellPicker unexpected work

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I am using vtkCellPicker in my project, and I find it unexpected work.

The code to reproduce my problem is:

import vtk

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(10)

pointPolyData = vtk.vtkPolyData()
pointPolyData.SetPoints(vtk.vtkPoints())
pointPolyData.SetVerts(vtk.vtkCellArray())
pointPolyData.GetPoints().InsertNextPoint(0, 0, 0)
pointPolyData.GetVerts().InsertNextCell(1)
pointPolyData.GetVerts().InsertCellPoint(0)
pointMapper = vtk.vtkPolyDataMapper()
pointMapper.SetInputData(pointPolyData)
pointActor = vtk.vtkActor()
pointActor.SetMapper(pointMapper)
pointActor.GetProperty().SetColor(255, 255, 0)
pointActor.GetProperty().SetPointSize(10)
pointActor.GetProperty().SetRepresentationToPoints()
pointActor.GetProperty().RenderPointsAsSpheresOn()

renderer = vtk.vtkRenderer()
renderer.AddActor(lineActor)  ########################### order
renderer.AddActor(pointActor) ##########################
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.SetTolerance(0.05)
    picker.Pick(pos[0], pos[1], 0, renderer)
    actor = picker.GetProp3D()
    if actor == lineActor:
        print('line')
    elif actor == pointActor:
        print('point')
    else:
        print('none')

renderWindowInteractor = vtk.vtkRenderWindowInteractor()
renderWindowInteractor.AddObserver("MouseMoveEvent", mousemove)

style = vtk.vtkInteractorStyleImage()
renderWindowInteractor.SetInteractorStyle(style)
renderWindowInteractor.SetRenderWindow(renderWindow)
renderWindowInteractor.Initialize()
renderWindowInteractor.Start()

Please have a look for the following figure:

image

In the above figure, I can pick the point in the white arrow. However, I can only pick line for the blue arrow, but I expect the blue arrow can pick the point.

I find it may be caused by the order to add point and line. If I change the order to:

renderer.AddActor(pointActor)
renderer.AddActor(lineActor)

It can pick point and 'line` as what I expect.

However, in my thought, the order to add point/line should have no effect for my situation. Because, the position of blue arrow is more close to the point than the line.

Then, I have a look into c++ code. After debug, I find vtkCellPicker actually picked both point and line, and add it to Prop3Ds (vtkPicker.cxx line 689).
Then, in the GetViewProp, it return this->Path->GetFirstNode()->GetViewProp(), it only return the first node rather than to calculate the distance between picked prop and pick position.

How can I do to pick the point at the position of blue arrow?

Any suggestion is appreciated~~~