Question

Is there a way that I can make VTK have the Y axis go down (when increasing values) rather than up?

I d like my VTK windows to match my non-VTK windows in displaying data, which all have the Y axis going down.

Answer 1

Depending on what exactly you re trying to do, you can get away with manipulating your camera.

Try something like this:

// To look "into" the X axis, with Y-axis pointing downwards
vtkCamera * cam = myRenderer->GetActiveCamera();

cam->SetPosition(1, 0, 0);
cam->SetFocalPoint(0, 0, 0);
cam->SetViewUp(0, -1, 0);

// To view the full bounds of your scene
myRenderer->ResetCamera();

Manipulating these ivars, you should be able to work things out quite easily. If you want to do something more complex, you can set a vtkTransform to the camera using camara->SetUserTransform() and manipulate the transform instead of trying to work out camera positions.

Note however, that VTK always assumes a right-handed coordinate system. In my above example looking into X and down on Y, the Z axis increases towards the left of the screen. This may cause some confusion if you re working with a left-handed system.

Answer 2

I m not familiar with VTK, but the function SetReverseYAxis() might be what you need.

Answer 3

You might consider the newer chart code in VTK, such as vtkChartXY. I added a test showing a simple line plot on a 3D scene, TestChartsOn3D.cxx, and the vtkAxis class is designed to allow you to set a minimum and maximum going in either direction. This would be entirely independent of the 3D scene, but you could do whatever you wanted there to make it match the 2D chart or not. You would need to use VTK 5.8.0 or later though.

Answer 4

In my situation, I am using QVtkWidget to display DICOM Axial volume with direrions [-1,-1, 1]. This is what works for me:

vtkSmartPointer<vtkImageViewer2> imageViewer= 
                            vtkSmartPointer<vtkImageViewer2>::New();
vtkCamera * cam = imageViewer->GetRenderer()->GetActiveCamera();
cam->SetFocalPoint (0, 0, 0);
cam->SetPosition   (0, 0, -1); // Camera in Z so it display XY planes. 
cam->SetViewUp     (-1, 0, 0); // Up direction is the X not the y.  
imageViewer->GetRenderer()->ResetCamera( );

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