How to change the rotation center point for vtkTransform?

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1

For example, I have a cylinder, whose center point is (0, 10, 0). I want this cylinder can rotation 30 degree along x axis with (0, 10, 0) as the rotation center. My code is:

import vtkmodules.all as vtk

cylinder = vtk.vtkCylinderSource()
cylinder.SetCenter(0, 10, 0)
cylinder.SetRadius(5)
cylinder.SetHeight(10)
cylinder.SetResolution(100)
cylinder.Update()

cylinderMapper = vtk.vtkPolyDataMapper()
cylinderMapper.SetInputData(cylinder.GetOutput())
cylinderActor = vtk.vtkActor()
cylinderActor.SetMapper(cylinderMapper)
cylinderActor.GetProperty().SetOpacity(0.3)

########################################################
# rotation 
transform = vtk.vtkTransform()
transform.RotateX(30)
cylinderActor.SetUserTransform(transform)
########################################################


def Line(p0, p1, c):

    line = vtk.vtkLineSource()
    line.SetPoint1(p0[0], p0[1], p0[2])
    line.SetPoint2(p1[0], p1[1], p1[2])
    line.Update()

    mapper = vtk.vtkPolyDataMapper()
    mapper.SetInputData(line.GetOutput())
    actor = vtk.vtkActor()
    actor.SetMapper(mapper)
    actor.GetProperty().SetColor(c[0], c[1], c[2])
    return actor

x = Line(p0=[0, 0, 0], p1=[20, 0, 0], c=[1, 0, 0])
y = Line(p0=[0, 0, 0], p1=[0, 20, 0], c=[0, 1, 0])
z = Line(p0=[0, 0, 0], p1=[0, 0, 20], c=[0, 0, 1])

renderer = vtk.vtkRenderer()
renderer.AddActor(cylinderActor)
renderer.AddActor(x)
renderer.AddActor(y)
renderer.AddActor(z)

renWin = vtk.vtkRenderWindow()
renWin.AddRenderer(renderer)
iren = vtk.vtkRenderWindowInteractor()
iren.SetRenderWindow(renWin)
iren.SetInteractorStyle(vtk.vtkInteractorStyleTrackballCamera())
iren.Initialize()
iren.Start()

The final result is:

image

We can see that the rotation center point is (0, 0, 0). How can I set the rotation center point to (0, 10, 0). I hope I can ahieve the following picture:

image

The above figure is obtained using vtk3DProp::SetOrigin & vtk3DProp::RotateX. How can I achieve the same result using vtkTransform and SetUserTransform.

Ang suggestion is appreciated~~~

2

Hello,

A rotation is always with respect to (0,0,0). Hence, to effect a rotation centered at (0,10,0), you have to compose three transforms: 1) translate by (0,-10,0); 2) rotate; 3) translate by (0,10,0).

transform = vtk.vtkTransform()
transform.Translate(0,10,0)
transform.RotateX(30)
transform.Translate(0,-10,0)
cylinderActor.SetUserTransform(transform)

No, it’s not inverted. Remember the linear algebra: the first transform is the last in effect.

cheers,

Paulo

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