[Paraview] Is the VIEW-UP vector updated automatically?

[Utkarsh Ayachit]

The meaning of azimuth, elevation etc. is indeed same with VTK and
ParaVIew. ParaView uses the same code for Camera as in VTK, so there's
no different there. Here's some explanation on the inner workings of
the camera:

+ The camera->ViewUp is used by vtkCamera as a "hint" for the up
direction. Thus, it is need not always be orthogonal to the view
direction (defined by camera position and camera focal point). Unless
the ViewUp is parallel to the view -direction, the vtkCamera will
automatically compute the true "viewup" internally using
vtkCamera::ViewUp as a hint.
+ You can use cam.OrthogonalizeViewUp() to force the vtkCamera to
update the VIewUp based on the internally used ViewUp.

e.g.

>>> cam = GetActiveCamera()
>>> cam.SetPosition(0, 3, 3)
>>> Render()
>>> cam.GetViewUp()
(0.0, 1.0, 0.0)
>>> cam.OrthogonalizeViewUp()
>>> cam.GetViewUp()
(0.0, 0.7071067811865476, -0.7071067811865476)

I am not sure I observe the same problem as you mention with Azimuth/Roll.

Utkarsh

On Mon, Oct 6, 2014 at 8:25 PM, Kazuyoshi Furutaka
<furutaka.kazuyoshi at jaea.go.jp> wrote:
> Could someone tell me whether the meanings of the azimuth and
> the elevation in ParaView the same as those in VTK (or "The
> Visualization Toolkit" book, 4th ed.) or not?
>
> In the book it reads:
> "Changing the \textit{azimuth} of a camera rotates its position
> around its view up vector, centered at the focal point.  Think
> of this as moving the cmaera to the left or right while always
> keeping the distance to the focal point constant.  Changing a
> camera's \textit{elevation} rotates its position around the cross
> product of its direction of projection and view up centered at the
> focal point.  This corresponds to moving the camera up and down.
> To \textit{roll} the camera, we rotate the view up vector about
> the view plane normal.  Roll is sometimes called twist."
>
> I sometimes observe that (in the Multi Slice view,) Azimuth()
> "rolls" instead of moving the camera left/right.
>
> That's why I want to understand the geometry of view-up, direction
> of projection, and so on...
>
> Kazuyoshi
>
>
> From: Kazuyoshi Furutaka <furutaka.kazuyoshi at jaea.go.jp>
> Subject: Re: [Paraview] Is the VIEW-UP vector updated automatically?
> Date: Tue, 07 Oct 2014 08:57:30 +0900 (JST)
>
>> I just want to write a Python macro to change/rotate the camera
>> position using Azimuth() and Elevation().
>>
>> In addition to the following:
>>
>>> I'm observing a curious behavior of paraview.simple.Azimuth();
>>> camera is NOT moving left/right.
>>
>> I sometimes get the following message
>>
>>  Warning: In /home/furutaka/work/ParaView/ParaView.git/VTK/Rendering/Core/vtkRenderer.cxx, line 1030
>> vtkOpenGLRenderer (0xa702510): Resetting view-up since view plane normal is parallel
>>
>> and am wondering how can the view-up be parallel to the view-plane
>> normal...
>>
>> My understanding is that the view-up is (always) perpendicular to
>> the direction of projection (pointing upward of the computer display)
>> and therefore parallel to the view-plane, so the view-up should always
>> be normal to view-plane normal.
>> Isn't the view-plane normal parallel to the direction of projection?
>> Isn't the view-plane parallel to the front/back clipping planes?
> --
> Kazuyoshi Furutaka
> furutaka _dot_ kazuyoshi _at_ jaea _dot_ go _dot_ jp
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