[vtkusers] Actors in front of camera clipped despite ResetCameraClippingRange()
Elvis Stansvik
elvis.stansvik at orexplore.com
Tue Jun 21 12:27:22 EDT 2016
2016-06-21 18:25 GMT+02:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
> 2016-06-21 17:44 GMT+02:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
>
>> Den 21 juni 2016 4:45 em skrev "Ken Martin" <ken.martin at kitware.com>:
>> >
>> > That image doesn't match what I think you are saying, so maybe you can
>> help me understand. You mention the camera is positioned on a cylinder of
>> radius 3.0 and from your code it looks like the focal point is not changing.
>> >
>> > If that is true then at some point some of the cones will be behind
>> your camera. For example if your focal point was (0,0,0) and your camera
>> was at (3,10,0) then you would be looking mostly down the y axis and from
>> your code you have a cone positioned at (0,20,0) which would be behind you.
>> >
>> > Having said all that your image looks funny anyhow. With a parallel
>> projection all the cones should look the exact same aside from clipping but
>> the first cone really looks off from the rest and the others are all
>> identical so something is off.
>> >
>> > I did look through that code and it looks reasonable to me (the patch
>> referenced is not correct BTW, parallel projection still requires proper z
>> buffer scaling and clipping) If you could provide a few more images from
>> different viewpoints, ideally with the resulting camera
>> >
>> > clipping range
>> > parallel scale
>> > position
>> > focal point
>> >
>> > for those images that would help me see what is going on.
>>
>> Thanks a lot for taking the time Ken. You're right of course about cones
>> being behind me. I think what I meant was I'm never inside a cone.
>>
>> I'll try to make a minimal test case when I get home, as I'm on the bus
>> and only have my phone right now.
>>
> Here's a minimal test case where the camera is positioned to look "down"
> on the stack of cones, the stack is cut off due to clipping (see attached
> .png):
>
> from vtk import vtkRenderer, vtkRenderWindow, vtkRenderWindowInteractor
> from vtk import vtkConeSource, vtkActor, vtkPolyDataMapper
>
> renderer = vtkRenderer()
> renderWindow = vtkRenderWindow()
> renderWindow.SetSize(500, 1000)
> renderWindow.AddRenderer(renderer)
>
> interactor = vtkRenderWindowInteractor()
> interactor.SetRenderWindow(renderWindow)
>
> # Create a stack of 40 cones along the Y axis
> for i in range(-20, 20):
> coneSource = vtkConeSource()
> coneSource.SetDirection(0, 1, 0)
> coneSource.SetResolution(8)
> coneSource.SetCenter(0, i, 0)
>
> coneMapper = vtkPolyDataMapper()
> coneMapper.SetInputConnection(coneSource.GetOutputPort())
>
> coneActor = vtkActor()
> coneActor.SetMapper(coneMapper)
>
> renderer.AddActor(coneActor)
>
> # Position camera at (3.0, 10.0, 0), looking "down" along the stack
> camera = renderer.GetActiveCamera()
> camera.SetParallelProjection(True)
> camera.SetPosition(3.0, 10.0, 0.0)
> camera.SetFocalPoint(0.0, 0.0, 0.0)
> camera.SetParallelScale(5.0)
>
> # Reset camera clipping range
> renderer.ResetCameraClippingRange()
>
> # Print some camera info
> print(camera)
>
> interactor.Start()
>
Forgot to include the output from the test (the printing of the camera):
vtkOpenGLCamera (0x2130810)
Debug: Off
Modified Time: 17946
Reference Count: 2
Registered Events: (none)
ClippingRange: (0.0531862, 53.1862)
DirectionOfProjection: (-0.287348, -0.957826, 0)
Distance: 10.4403
EyeAngle: 2
FocalDisk: 1
FocalPoint: (0, 0, 0)
ViewShear: (0, 0, 1)
ParallelProjection: On
ParallelScale: 5
Position: (3, 10, 0)
Stereo: Off
Left Eye: 1
Thickness: 53.133
ViewAngle: 30
UseHorizontalViewAngle: 0
UserTransform: (none)
(none)
FreezeFocalPoint: (none)
ViewPlaneNormal: (0.287348, 0.957826, -0)
ViewUp: (0, 1, 0)
WindowCenter: (0, 0)
UseOffAxisProjection: (0)
ScreenBottomLeft: (-0.5, -0.5, -0.5)
ScreenBottomRight: (0.5, -0.5, -0.5)
ScreenTopRight: (0.5, 0.5, -0.5)
EyeSeparation: (0.06)
WorldToScreenMatrix: (0x2130a50
Debug: Off
Modified Time: 12739
Reference Count: 1
Registered Events: (none)
Elements:
1 0 0 0
0 1 0 0
0 0 1 0
0 0 0 1
)
EyeTransformMatrix: (0x2130b40
Debug: Off
Modified Time: 12741
Reference Count: 1
Registered Events: (none)
Elements:
1 0 0 0
0 1 0 0
0 0 1 0
0 0 0 1
)
ModelTransformMatrix: (0x2130c30
Debug: Off
Modified Time: 12743
Reference Count: 1
Registered Events: (none)
Elements:
1 0 0 0
0 1 0 0
0 0 1 0
0 0 0 1
)
ProjectionTransform: (0x2131170
Debug: Off
Modified Time: 12748
Reference Count: 1
Registered Events: (none)
Inverse: (0)
Matrix: (0x21312a0)
Debug: Off
Modified Time: 17947
Reference Count: 1
Registered Events: (none)
Elements:
1 0 0 0
0 1 0 0
0 0 1 0
0 0 0 1
Input: (0)
InverseFlag: 0
NumberOfConcatenatedTransforms: 0
)
Elvis
>
> But I'm beginning to think this is maybe just a misunderstanding on my
> part. Perhaps this clipping is inevitable and expected when using parallel
> projection?
>
> Thanks in advance,
> Elvis
>
> Elvis
>>
>> >
>> > Thanks
>> > Ken
>> >
>> >
>> >
>> >
>> >
>> > On Tue, Jun 21, 2016 at 7:06 AM, Elvis Stansvik <
>> elvis.stansvik at orexplore.com> wrote:
>> >>
>> >> Hi all,
>> >>
>> >> I have a setup where the camera always moves on a cylinder of radius
>> 3.0 around my subject (just testing with a stack of cones at the moment).
>> The focal point is always positioned along the Y axis, and the camera may
>> be moved up and down independent of the focus point, but the camera is
>> always at a distance of 3 from the Y axis.
>> >>
>> >> As soon as the user moves the camera, I reset the camera clipping
>> range with ResetCameraClippingRange(). Despite this, when the camera and
>> the focal point are far away from eachother, the actors (my stack of cones)
>> get clipped by the near plane for some reason.
>> >>
>> >> See the attached screenshot which shows the clipping.
>> >>
>> >> What I'm doing to my camera (in response to Shift+mouse drag in my
>> custom interactor) to end up in this situation is just:
>> >>
>> >> camera = renderer.GetActiveCamera()
>> >> (x, y, z) = camera.GetPosition()
>> >> camera.SetPosition(x, y - self.PanningFactor * dy, z)
>> >> renderer.ResetCameraClippingRange()
>> >>
>> >> and I've verified that the camera is always at a distance of 3.0 from
>> the Y axis.
>> >>
>> >> The cones I'm using in this test were created with:
>> >>
>> >> for i in range(-10, 20):
>> >> coneSource = vtkConeSource()
>> >> coneSource.SetDirection(0, 1, 0)
>> >> coneSource.SetResolution(8)
>> >> coneSource.SetCenter(0, i, 0)
>> >>
>> >> coneMapper = vtkPolyDataMapper()
>> >> coneMapper.SetInputConnection(coneSource.GetOutputPort())
>> >>
>> >> coneActor = vtkActor()
>> >> coneActor.SetMapper(coneMapper)
>> >>
>> >> widget.renderer.AddActor(coneActor)
>> >>
>> >> I don't understand why I see clipping occur here, since I'm using
>> ResetCameraClippingRange, and nothing is behind the camera. The radius of
>> these cones is the default (0.5).
>> >>
>> >> It's probably something stupid, but any advice is much appreciated.
>> >>
>> >> Elvis
>> >>
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>> >
>> >
>> >
>> > --
>> > Ken Martin PhD
>> > Chairman & CFO
>> > Kitware Inc.
>> > 28 Corporate Drive
>> > Clifton Park NY 12065
>> > 518 371 3971
>> >
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