A procedural tool used to generate road and bridge in Houdini based on any curve. If the vertex is higher than certain user-defined threshold, it will generate pillar under the bridge, forming a bridge. Users can adjust the width of the bridge. I think the most interesting and difficult part in this tool is to orient the lower part of the pillar. To solve that, what I basically do is using cross(cross(tangent, normal), up) then I get the direction I want.