Constructing a tunnel crossection from conditional points


Just started evaluating using grasshopper for infrastructure modelling in our department.

Is there a way to construct points dependent on each other? For example: Point A (0,0,0) and Point B = (+2,0,0) so if Point A changes, point B follows along but at a 2 m offset.

I basically just want the X coordinate from the point output as an input for another point.

What I’m trying to do is create a cross-section of a tunnel. Surfaces will be constructed between the different points and swept along a centerline.

Another problem I have is that I can’t seem to create a half-ellipse. There’s only an ellipse parameter tool and I cant figure out how to cut that in half (its for the roof part). Probalby need to use the nurbs curve tool but a half-ellipse would be much easier.

Sorry for the horrible drawing. Just quickly sketched my thought process. You dont have to pay too much attention to it.


Perhaps look here

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Thanks, that was fast!

I’ll look into that concerning the roof part.

I did just after I posted this realize that you could deconstruct a point and pull values from that.

You can Move (copy) points instead of constructing new ones, so when the reference point is moved all the others that depend on it will also move.

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This is a great tip, thank you!