how to control the orient of extrusion on a surface

I have a problem with controlling the extruding directions on a looped surface.....

Is it a problem with my base geometry..?
or there is a way to control the orientation of the extrusion...

the above surface is built by 2rail sweep..

I started by dividing the surfaces into 70x4 subsurfaces, I divides the edge of the subsurfaces and build vector from the points

but when i try to extrude a curve ..a rectangular .... some of the extrusion is out of my expectation...some of them are rotated...

it didnt help even i rebuilt the base surface

the tube roatated in differet direction , leaving a ugly gap

Attachments:

surface_problem.ghx, 595 KB

Replies to This Discussion

Permalink Reply by Jon Mirtschin on January 9, 2012 at 1:52am

Is there a rhino file to accompany your definition?

You could consider StructDrawRhino for orienting extrusions on a surface:

Permalink Reply by harmony on January 9, 2012 at 5:05am

thanks a lot~~~ sorry that i didnt upload the 3dm file as the file is too big..

later , i found out that although i gave vector showing the direction of extrusion..

(then by plane normal to get the plane..)
but i didnt define the xy axis of any of the plane
so planes rotate around the normal...

then i fix it by defining the x axis...
using 'surface cp' the 'vector 2pt' to get the axis..

so now..all the rods extrude along the base surface.....

i will upload the definition and rhino file later