# Thread: How to change poliline to get the parabolic shape

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## How to change poliline to get the parabolic shape

I have a lot of polylines that need to be converted to the vertical parabolic shape of line sag
and then I want to create a pipe with a small diameter tube along.
How can I use lisp to select those lines so it will perform the above 2 requests?
I have attached the reference file below

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## Re: How to change poliline to get the parabolic shape

The mathematical term for that curve is called a catenary curve. If all you want is 2D lines, then you can use the attached lisp. But if you want actual 3D cables, then you will need a much more robust solution. I recommend AUD from Spatial Business Systems.

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## Re: How to change poliline to get the parabolic shape

In roadway design vertical parabolic curves for elevations are the standard used in Civil 3D to create profile sections.
You should be able to use that for the profile sections with straight segments in the plan views.
One of the 3 types of curves described in Civil 3D help: https://help.autodesk.com/view/CIV3D...5-D18C60F9ECCB

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## Re: How to change poliline to get the parabolic shape

How I can use this lisp? What input "Tension in the cable & cable weight per unit length"
I only want to change to a catenary curve.

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Originally Posted by Tom Beauford
In roadway design vertical parabolic curves for elevations are the standard used in Civil 3D to create profile sections.
You should be able to use that for the profile sections with straight segments in the plan views.
One of the 3 types of curves described in Civil 3D help:
How to I change multiple line, I don't want create profiles sections because I have a lot of polyline.

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## Re: How to change poliline to get the parabolic shape

Originally Posted by dien2708736511
How I can use this lisp? What input "Tension in the cable & cable weight per unit length"
I only want to change to a catenary curve.
You can get cable tensions and weight off the internet. Tension can be 100-500 lbs/sq ft for a transmission line. Weight for 1000MCM is 1.063 lbs per ft. If you don't care about accuracy, then just input any number and see if it looks good. When you figure it out for one, then you can use that same number for the other curves. Note that it doesn't change existing polylines. It creates new ones.