Texts and 3D linestyles on lines protrude perpendicular to the line. This setting controls the direction in which they protrude in order to maximize readability.
Name
Description
vertical
With that setting you get more sense of the orientation of the line in space. The lines stay fixed in space also when the observer camera moves or rotates.
perpendicularToCamera
This maximises the size in which a text or line style can appear (it minimizes paralax shrinking), but it can look wobbly, especially when the observer camera moves or rotates. The camera that is used is decided by CameraForAutomaticOrientation.