Text orientation in space or towards observer
With Billboarding = TRUE, text objects are always facing the observer. With Billboarding = FALSE, text objects retain their orientation relative to other objects.
Often, text objects in 3D are used to label certain places in a graphic (note that objects can contain a title, so text objects are usually only necessary for additional descriptions). In this case, it is desirable that they always face the observer to be readable and not rotate along with the rest of the scene. This is the default behavior. To get text objects that are actually part of the scene in the sense that rotating the scene also rotates the texts, set Billboarding = FALSE.
In the following image, the prime numbers use Billboarding = TRUE, while other numbers do not:
plot(plot::Text3d(expr2text(i), [3*i, 0, 0], TextOrientation = [1, 0, 0, 0, 1, 0], Billboarding = isprime(i)) $ i = 1..15, TextFont = , Scaling = Constrained, Axes = None)
Note that text objects with Billboarding = TRUE ignore TextOrientation.