This iExpression changes the meaning of the x, y, and z value of the property such that you can easily animate it along a cylinder surface. Technically speaking the iExpression turns your coordinate system into a cylindrical coordinate system. Simply speaking, you can animate the property via keyframes as usual, but the values have a new meaning: Applied to the position of a layer, the x and y position now do not move the layer left/right and up/down anymore; instead they move the layer along the surface of the cylinder. The radius of the cylinder is given in the z component. In order to orient the layers correctly on the cylinder surface, apply the "Look At Line 3D" iExpression to their orientation and choose as first point of the line the center of the sphere and as second point an arbitrary point exactly above or below it (e.g. the center with a value of 100 added to its y value). If you want to move or rotate the cylinder, its best to set the center to (0,0,0), then create a new NULL object, make it 3D and parent the layers on the cylinder surface to this NULL. During the parenting keep the alt or option key pressed. Then the position of the NULL becomes the center of the cylinder and you can move or rotate it using the transform controls of the NULL.
is the center of the cylinder along whose surface the property is moved.
Scale Radius (%)
allows to scale the circle around which the cylinder wraps. If the x and y values are not identical you obtain squeezed circles i.e. ellipses.