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IDProjectCategoryView StatusDate SubmittedLast Update
0009740VTK(No Category)public2009-10-20 08:582016-08-12 09:55
Reporteredice 
Assigned ToKitware Robot 
PrioritynormalSeverityminorReproducibilityalways
StatusclosedResolutionmoved 
PlatformOSOS Version
Product Version 
Target VersionFixed in Version 
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Summary0009740: vtkInteractorStyleTerrain generates errors "Resetting view-up since view plane normal is parallel"
DescriptionWhen you look down the "north pole" with the Terrain interactor style, you get a lot of warning messages like so:

Warning: In /opt/vtk_5_4_2/VTK/Rendering/vtkRenderer.cxx, line 1051
vtkOpenGLRenderer (0x9dff598): Resetting view-up since view plane normal is parallel



In vtkRenderer.cxx, there is this test:
  vup = this->ActiveCamera->GetViewUp();
  if ( fabs(vtkMath::Dot(vup,vn)) > 0.999 )
    {
    vtkWarningMacro(<<"Resetting view-up since view plane normal is parallel");
    this->ActiveCamera->SetViewUp(-vup[2], vup[0], vup[1]);
    }

So, vtkRenderer.cxx starts to panic when the dot > 0.999, which I will show happens before the Terrain's limit of 179 degrees.





There is code in vtkInteractorStyleTerrain that, quote:

  // Move the camera.
  // Make sure that we don't hit the north pole singularity.

but, it does not do the job well enough.
This is the code that avoids the singularity:

  double angle = vtkMath::DegreesFromRadians( acos(vtkMath::Dot( dop, vup) ) );
  if ( ( angle + e ) > 179.0 ||
       ( angle + e ) < 1.0 )
    {
    e = 0.0;
    }

I added some printouts after this code:
    cout << "dot " << fabs(vtkMath::Dot( dop, vup)) << " angle+e = " << angle << " + " << e << " = " << angle+e << endl;

Note, the dot represents the past, angle+e represents the future.


I saw these messages as i rotated towards the north pole:

dot 0.997361 angle+e = 175.836 + 0.640569 = 176.477
dot 0.99811 angle+e = 176.477 + 0.640569 = 177.117
dot 0.998735 angle+e = 177.117 + 0.640569 = 177.758
Warning: In /opt/vtk_5_4_2/VTK/Rendering/vtkRenderer.cxx, line 1051
vtkOpenGLRenderer (0x9dff598): Resetting view-up since view plane normal is parallel
dot 0.999235 angle+e = 177.758 + 0.640569 = 178.399

So, dot=0.999234 after 0.640569 was added to 177.117 to get angle=178.399

We have not reached 179 degrees and we have surpassed dot=0.999234.



So the solution appears to be either change vtkRenderer.cxx's limit to 0.9999 or high (keep adding 9's), OR to change the Terrain's test to 2 and 178 degrees.

Steps To Reproduce
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Issue History
Date ModifiedUsernameFieldChange
2009-10-20 08:58ediceNew Issue
2009-10-20 09:11ediceNote Added: 0018123
2011-06-16 13:11Zack GalbreathCategory => (No Category)
2016-08-12 09:55Kitware RobotNote Added: 0037110
2016-08-12 09:55Kitware RobotStatusexpired => closed
2016-08-12 09:55Kitware RobotResolutionopen => moved
2016-08-12 09:55Kitware RobotAssigned To => Kitware Robot

Notes
(0018123)
edice   
2009-10-20 09:11   
If Terrain's test is changed, then 2 and 178 (as prev stated) isn't enough.

3 and 177 degrees appears to be enough. Someone with a calculator could probably work out the exact limits.
(0037110)
Kitware Robot   
2016-08-12 09:55   
Resolving issue as `moved`.

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