VTK rotation operation Using Python

Question

I would like to ask a question on VTK operations. I have one VTK file and I want to get many images, each taken from a different angle to create a movie of that image.

I have created the following codes (see below). The problem is that although different coordinates will rotate the image to the angles that I want, the zooming is a bit off. So images on some angles appear to be "zoomed in", but other images with different angles appear to be "zoomed out".

I am not sure how should I set all the images to have the same "zooming" scale. Help will be much appreciated. Thank you.

def rotateSave(data, coordinates, filename):

    ### Set up things

    ren = vtk.vtkRenderer()
    renWin = vtk.vtkRenderWindow()
    renWin.AddRenderer(ren)
    iren = vtk.vtkRenderWindowInteractor()
    iren.SetRenderWindow(renWin)
    mapper = vtk.vtkPolyDataMapper()
    mapper.SetInputData(data)
    actor = vtk.vtkActor()
    actor.SetMapper(mapper)

    ### Translate and Rotate

    center_x, center_y, center_z = actor.GetCenter()
    ren.AddActor(actor)
    w = vtk.vtkTransform()
    w.Translate(-center_x, -center_y, -center_z)
    w.RotateX(coordinates[0])
    w.RotateZ(coordinates[2])
    actor.SetUserTransform(w)

    ### Save

    renWin.Render()
    w2if = vtk.vtkWindowToImageFilter()
    w2if.SetInput(renWin)
    w2if.Update()
    writer = vtk.vtkPNGWriter()
    writer.SetFileName(filename.png)
    writer.SetInputData(w2if.GetOutput())
    writer.Write()

    return

Answer 1

In order to set all the images to have the same "zooming" scale, you could reset the camera in the renderer, something like this:

(...)
### Save
ren.ResetCamera()
renWin.Render()
w2if = vtk.vtkWindowToImageFilter()
(...)

Or if you want you can always change the zooming factor:

ren.GetActiveCamera().Zoom(1.2) #increase zoom
ren.GetActiveCamera().Zoom(0.8) #decrease zoom

Please check the vtkCamera ( https://www.vtk.org/doc/nightly/html/classvtkCamera.html ) class, it has some examples.