centering (justification/alignment) of vtkFollower text

[dmgroppe (David Groppe)]

Thanks very much, Alison! However, it appears that vtkBillboardTextActor3D has some issues with occlusion when using it with raycasting:

vtkBillboardTextActor3D text always renders behind raycast volume

Displaying labels correctly is extremely difficult. I’ve spent a lot of time experimenting with different options for markup display in 3D Slicer, but each option has different limitations. To tackle occlusion: To make sure the labels are not occluded, you can display 3D label actors on a separate layer or use 2D actors. However, then you need to manually hide the actors when the corresponding point of interest is occluded. In general, determining if a certain point is occluded is a very costly…

@lassoan, I like your suggestion of using vtkLabelPlacementMapper, but I can’t figure out how to control the size of the text or its alignment/justification.