A "spine" is a curve that represents a series of invisible planes, with each plane being perpendicular to the spine curve. (If the spine is a straight line, then all the planes are parallel to each other. If the spine is a circle, then all the planes are radial. When the spine is a freeform curve, then the planes are not parallel and they follow the shape of the curve.)I also want to know that how changing the spine element effects the sweep.