Setting the Orientation of a Spined Surface

When using the Spined Surface command, you can control the way the boundary curve moves along the spine. To do this, a local reference system is attributed to the spine. The local system is initially calculated at the first endpoint of the spine curve and then moved along it. The way the local system is moved along the spine curve depends on the option selected in the Orientation drop-down list (under More Options).

Let us see what happens in the model of the following illustration (to try it, load file "spsrf_orientation.e3"), where the blue curve is the spine, the red curve is the boundary and the green curve is the drive.

Automatic	The X direction of the local system is determined as follows: If the spine is a plane curve or curve chain, the X direction is the normal to the plane in which the spine lies If the spine is 3D, the X direction of the local system is calculated in such a way that the plane perpendicular to the plane tangent to the spine and through X follows a straight path
Defined with curves	The X direction of the local system is calculated by joining points on the spine to the corresponding points on a selected curve or curve chain (which may also be the same as the drive). Select the curve (you can change the selected curve by right-clicking on 1st Drive in the selection list and selecting Reset in the context menu).
Intrinsic system	The reference system is the one defined by the spine curve.