[vtk-developers] Bug in vtkCamera::Elevation

[Xabi Riobe]

I pushed a fix : https://gitlab.kitware.com/vtk/vtk/merge_requests/1194

2016-02-05 13:59 GMT+01:00 Xabi Riobe <xabivtk at gmail.com>:

> 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
>> 28 Corporate Drive
>> Clifton Park, NY 12065
>> will.schroeder at kitware.com
>> http://www.kitware.com
>> (518) 881-4902
>>
>
>
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