# 4-Rail Modification

In this Grasshopper Lesson, I will show you some techniques which you can use to modify the rail curve. By modifying the rail curve you can also design new parametric models. First, you will learn how to model the surface and then we will convert the surface to a stadium.

36 Minutes

166 MB

### Free Weekly Scripts

• ##### Chris-Ryan

Hello,
I’m having a problem with the curve offset. The planes of the curves are wrong, so I use the planes of the frames. But even when I apply the planes to the “offset” module, one of the curves is offset against the others.

• ##### rezae

Hi Chris
The reason arise when we split our surface with planes… So basically periodic surfaces have different directions at the joint so i just simply shift the planes a bit to avoid this direction issue

• ##### Christine

Attachment  screenshot.png

Hello, just having a problem with one of the curves from the section, seems to have flipped?

• ##### rezae

Hi Christine,
Yes, you can use Flip Curve to solve this issue and if you send me your gh file I can tell you how to fix it.

• ##### rezae

I’ve highlighted new changes

• ##### felo68

Attachment  RAILMODY.zip

Hi Rezae,
Altough I am following the lesson step by step, I am encountering this problem over and over and I haven’t figured out why. Could you take a look, please, and let me know where I am making a mistake?

• ##### rezae

Hi felon,
The base Polygon had fillet radius which prevents the lunch box to create 2D truss because when we create fillet the section will be curve instead of polylines and Lunchbox works with polylines only.
Please let me know if you have any problem.
I’ve emailed the edited version.

• ##### parametric

To Solve the Problem simply right click on options input of loft and select loft options. then select align section and hit commit changes. you can also connect a “loft options” component and set “Adjust” to true.

• ##### ferg-mu

Hi
Thanks for another great tutorial.
I’m having a problem when I go to create the 2D truss system.
For some reason the offset lines are all linking with each other creating a pretty crazy web… see image attached.

Also I had a bit of trouble getting all the lines to offset in the same direction so I created a list to isolate the line that was incorrect to amend this.
Let me know what you think I should do
(btw i decided to create a model that is much larger in scale)