[vtk-developers] Bug in vtkCamera::Elevation

[Xabi Riobe]

Ok now it looks clear to me, thanks for the explanation Will.

So i'll just fix the 90° issue.


2016-02-05 12:54 GMT+01:00 Will Schroeder <will.schroeder at kitware.com>:

> This is a known problem since 1993 when VTK was first written. It is
> presumed to be an application-level issue. That is, if you are flying over
> terrain, you do not want to be messing with the view up, otherwise the
> elevation, pitch, etc. lose their meaning.
>
> As evidence of this check out
> VTK/Interaction/Style/vtkInteractionStyleTerrain which has explicit
> commentary about dealing with the north pole singularity. Then look at
> vtkInteractorStyleTrackballCamera, vtkInteractorStyleJoystickCamera, etc.
> They all have explicit calls to camera->OrthogonalizeViewUp() which is
> added to address the view up singularity.
>
> Best,
> W
>
> On Thu, Feb 4, 2016 at 8:54 AM, Xabi Riobe <xabivtk at gmail.com> wrote:
>
>> Hi,
>>
>> There is an issue in vtkCamera::Elevation if the angle is 90.
>>
>> It is 100% reproductible with VS2013 if compiled in 64bits, otherwise the
>> rounding epsilon makes it work by chance.
>>
>> I'm willing to fix it in GitLab but first i would like your opinion about
>> the best way to do it.
>>
>> with a simple example of a plane in a renderer, and a call to
>> renderer->GetActiveCamera()->Elevation(90)
>>
>> What happens in the call stack of vtkCamera::Elevation :
>>    vtkCamera::SetPosition()
>>    vtkCamera::ComputeViewTransform
>>    vtkPerspectiveTransform::SetupCamera
>>
>>    vtkMath::Cross(viewUp,viewPlaneNormal,viewSideways);
>>
>> where viewUp and viewPlaneNormal are both (0,1,0)  so viewSideways is
>> (0,0,0) leading to bad camera parameters.
>> Here comes the VS13+64bits configuration case, when with others,
>> viewSideways is luckily different than 0
>>
>> What do you think of applying the rotation to the viewUp vector in
>> vtkCamera::Elevation before the call to SetPosition?
>> Should we put a warning in vtkPerspectiveTransform::SetupCamera
>> when vtkMath::Normalize returns 0?
>>
>>
>>
>>
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>
>
> --
> William J. Schroeder, PhD
> Kitware, Inc. - Building the World's Technical Computing Software
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