python vtk rotate actor about line

Question

I am new to python and VTK so please have patience :)

On short, I have an actor and I would like to rotate it about a line I drew using vtkLineSource(). I chose my start and end points and I drew the line. Now what I thought is (please correct me if I am wrong) that I should make an axis on the line and then apply the vtkTransformWXYZ() to rotate about the axis. It does not work, it gives a weird rotation about the chosen point, but not the one I desire. I also tried defining the axis on the middle of the line I drew and apply the rotation on it, but when I try, it rotates about the global coordinates, and not the local. I also tried to give as input the point or the line, but again, the rotation is very weird.

Is there a way to define the line as an axis and rotate the actor about it? So far I tried like in the following examples: https://lorensen.github.io/VTKExamples/site/Python/PolyData/RotationAroundLine/ and https://lorensen.github.io/VTKExamples/site/Python/Rendering/Rotations/ but my actor always rotates in a weird way.

Could anyone help/point me in the right direction please?

Here is the part of my code where I am trying to rotate the actor…

###################### create line to rotate about and display it

    lineStart = [16.8879, -106.476, -782.449]       
    lineFinish = [-17.827, -92.2757, lineStart[2]]
    lineMiddle = [(lineStart[0]+lineFinish[0])/2, (lineStart[1]+lineFinish[1])/2, lineStart[2]]
    
    lineSource = vtk.vtkLineSource()
    lineSource.SetPoint1(lineStart)
    lineSource.SetPoint2(lineFinish)
    lineSource.Update()
    
    mapperLine = vtk.vtkPolyDataMapper()
    mapperLine.SetInputConnection(lineSource.GetOutputPort())
    
    actorLine = vtk.vtkActor()
    actorLine.SetMapper(mapperLine)
    actorLine.GetProperty().SetLineWidth(4)
    actorLine.GetProperty().SetColor(1,0,0)
    ren.AddActor(actorLine)

############# rotate about the line

    modelMapper = vtk.vtkPolyDataMapper()
    modelMapper.SetInputData(cleanFilter.GetOutput())

    modelActor = vtk.vtkActor()
    modelActor.SetMapper(modelMapper)
    
    modelAxesSource = vtk.vtkAxes()
    modelAxesSource.SetScaleFactor(100)
    modelAxesSource.SetOrigin(lineMiddle)

    
    modelAxesMapper = vtk.vtkPolyDataMapper()
    modelAxesMapper.SetInputConnection(modelAxesSource.GetOutputPort())

    modelAxes = vtk.vtkActor()
    modelAxes.SetMapper(modelAxesMapper)


    ren.AddActor(modelAxes)
    modelAxes.VisibilityOn()
    ##this did not work
    ##modelActor.SetOrientation(lineMiddle)
    ##modelActor.RotateZ(45)
    ##ren.AddActor(modelActor)

transform = vtk.vtkTransform()
    transform.RotateWXYZ(45, lineMiddle)
    transformFilter = vtk.vtkTransformPolyDataFilter()
    transformFilter.SetTransform(transform)
    transformFilter.SetInputConnection(cleanFilter.GetOutputPort())
    transformFilter.Update()
    
    NewMapper = vtk.vtkPolyDataMapper()
    NewMapper.SetInputConnection(transformFilter.GetOutputPort())
    
    actorRotated = vtk.vtkActor()
    actorRotated.SetMapper(NewMapper)

    
    ren.AddActor(actorRotated)

I have also tried the following:

    rotate = vtk.vtkRotationFilter()
    rotate.SetInputConnection(cleanFilter.GetOutputPort())
    rotate.SetAxisToY()
    rotate.SetCenter(lineMiddle)
    rotate.SetAngle(45)
    mapper = vtk.vtkDataSetMapper()
    mapper.SetInputConnection(rotate.GetOutputPort())
    actor = vtk.vtkActor()
    actor.SetMapper(mapper)
    ren.AddActor(actor)

but it does not display anything.

Any help is apreciated!

Thanks in advance, Diana

Answer 1

You may need to write some function like this:

    def rotate(obj, angle, axis=(1, 0, 0), axis_point=(0, 0, 0), rad=False):
        """Rotate around an arbitrary `axis` passing through `axis_point`."""
        if rad:
            anglerad = angle
        else:
            anglerad = np.deg2rad(angle)
        axis = utils.versor(axis)
        a = np.cos(anglerad / 2)
        b, c, d = -axis * np.sin(anglerad / 2)
        aa, bb, cc, dd = a * a, b * b, c * c, d * d
        bc, ad, ac, ab, bd, cd = b * c, a * d, a * c, a * b, b * d, c * d
        R = np.array(
            [
                [aa + bb - cc - dd, 2 * (bc + ad), 2 * (bd - ac)],
                [2 * (bc - ad), aa + cc - bb - dd, 2 * (cd + ab)],
                [2 * (bd + ac), 2 * (cd - ab), aa + dd - bb - cc],
            ]
        )
        rv = np.dot(R, obj.GetPosition() - np.array(axis_point)) + axis_point

        if rad:
            angle *= 180.0 / np.pi
        # this vtk method only rotates in the origin of the object:
        obj.RotateWXYZ(angle, axis[0], axis[1], axis[2])
        pbj.SetPosition(rv)

testing it using vedo:

from vedo import *

c1 = Cube() # vtkActor
c2 = c1.clone().c('violet').alpha(0.5) # make a clone copy

v = vector(0.2,1,0)
p = vector(1,0,0)
c2.rotate(90, axis=v, point=p)

l = Line(-v+p, v+p).lw(3).c('red') # vtkActor
show(c1, c2, l, axes=1)