TYPE: SOP
TITLE: Rails SOP

The Rails operation generates surfaces by stretching cross-sections between two 
rails.  The first input is the cross-section which will be replicated, 
and is typically placed in the XY plane. The second input are the rails along
which the cross-section is replicated.

Parameters:

    X-Section Groups - Subset of cross section geometry to use.
    Rail Groups      - Subset of rails geometry to use.
    Cycle Type       - How the cross-section should be applied to the rails.
    Sweep Along Pairs of Rails - Sweeps along rail 1 & 2, 3 & 4, 5 & 6 etc. 
                                 instead of 1 & 2, 2 & 3, 3 & 4 etc.
    Sweep Along First and Last Rail - Sweeps along the first and last rail.
    Stretch to Rails - Stretches cross-section geometry to rails geometry.
    Use Vertex       - Specifies two cross section vertices to be      
                       placed on rail1 and rail2 respectively.        
    Connection Vertices  - The vertices used by Use Vertex.   /vertex1 /vertex2
    Scale                - Scales the cross section in x & y.          /scale
    Roll                 - Rolls the cross section in z.               /roll
    Fix Flipping         - Tries to correct flipped normals.
    Use Direction        - Uses specified direction vector.
    Direction            - Direction to point cross sections.  /dirx /diry /dirz
    Create Output Groups - Places created rails in a new primitive group.
    Group Name           - Name of group to create.

See also: Sweep, Skin
