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IDProjectCategoryView StatusDate SubmittedLast Update
0001432VTK(No Category)public2004-12-15 11:222016-08-12 09:54
ReporterKatharina.Quintus 
Assigned ToKitware Robot 
PrioritylowSeverityminorReproducibilityalways
StatusclosedResolutionmoved 
PlatformOSOS Version
Product Version 
Target VersionFixed in Version 
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Summary0001432: documentation of method SetParallelScale of vtkCamera not correct?
DescriptionThe documentation of the method SetParallelScale/ GetParallelScale in vtkCamera tells "Set/Get the scaling used for a parallel projection, i.e. the height of the viewport in world-coordinate distances."
I tried several times and I think it should say "... the half of the height of the viewport."
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Issue History
Date ModifiedUsernameFieldChange
2008-11-30 09:20Mathieu MalaterreAssigned ToMathieu Malaterre => François Bertel
2008-11-30 20:17François BertelAssigned ToFrançois Bertel =>
2009-07-14 04:25Paul MelisNote Added: 0016856
2010-07-27 15:56jjinnsoftNote Added: 0021501
2011-06-16 13:11Zack GalbreathCategory => (No Category)
2016-08-12 09:54Kitware RobotNote Added: 0036758
2016-08-12 09:54Kitware RobotStatusexpired => closed
2016-08-12 09:54Kitware RobotResolutionopen => moved
2016-08-12 09:54Kitware RobotAssigned To => Kitware Robot

Notes
(0016856)
Paul Melis   
2009-07-14 04:25   
I ran into this as well. The relevant code in vtkCamera::ComputePerspectiveTransform is

  if (this->ParallelProjection)
    {
    // set up a rectangular parallelipiped

    double width = this->ParallelScale*aspect;
    double height = this->ParallelScale;

    double xmin = (this->WindowCenter[0]-1.0)*width;
    double xmax = (this->WindowCenter[0]+1.0)*width;
    double ymin = (this->WindowCenter[1]-1.0)*height;
    double ymax = (this->WindowCenter[1]+1.0)*height;

    this->PerspectiveTransform->Ortho(xmin,xmax,ymin,ymax,
                                      this->ClippingRange[0],
                                      this->ClippingRange[1]);

Note that this leads to an orthographic view with height
  
  ymax - ymin
  = (WC[1]+1)*PS - (WC[1]-1)*PS
  = PS*WC[1] + PS - PS*WC[1] + PS
  = 2 * ParallelScale

So even though the parallel scale value is indeed taken as viewport height the computed orthographic projection results in a view twice as high.
(0021501)
jjinnsoft   
2010-07-27 15:56   
I also ran into this. I'm trying to capture 2D images with a specific dots per inch (the 3D model is in real-world millimeters). It seemed like my calculations to pass into this parameter were wrong by a factor of 2 and this explains why.
(0036758)
Kitware Robot   
2016-08-12 09:54   
Resolving issue as `moved`.

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