# Polyline Joined with Control Point Curve Breaks Calculation of Rail

**URL:** <https://discourse.mcneel.com/t/polyline-joined-with-control-point-curve-breaks-calculation-of-rail/218326>\
**Category:** Grasshopper\
**Tags:** curve, fillet, rhino7, polylines, join-curves\
**Created:** [April 23, 2026, 5:04pm UTC](https://discourse.mcneel.com/t/polyline-joined-with-control-point-curve-breaks-calculation-of-rail/218326 "2026-04-23T17:04:28Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![AA99](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/aa99/32/734371_2.png) [@AA99](https://discourse.mcneel.com/u/AA99)\
**Post date:** [April 23, 2026, 5:04pm UTC](https://discourse.mcneel.com/t/polyline-joined-with-control-point-curve-breaks-calculation-of-rail/218326/1 "2026-04-23T17:04:28Z")

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Hi everyone,

I’m trying to create an input for a polyline, and for now it’s working well. The fillets are generatin

[Track-Polylines\_1.5.gh](https://discourse.mcneel.com/uploads/short-url/GH8TsQhff95evPyicxg5q2Ljfz.gh) (40.5 KB)

g correctly, and I can place the rack along them.

The issue starts when I try to join a wiggly curve with the polyline. At that point, the fillets stop calculating properly, and the spacing of the elements (rack/bays) becomes inconsistent. Also, the connection between the polyline and the newly joined curve loses the fillet at that transition.

Does anyone know how I can fix this or approach it differently? I’d really appreciate the help.

(((I am not trying to add fillets to the control point curve but i want to join them together where only it is applied to the hard rigid polylines)))

 ![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/e/d/6/ed6badf946e2bd42ce982c19cc0cc35226f96fb9.png)

 ![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/f/d/8/fd81e454e6e1c3516e80540d02f0e35a54a4fde2.png)

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**Author:** ![leopoldomonzani](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/leopoldomonzani/32/637191_2.png) [@leopoldomonzani](https://discourse.mcneel.com/u/leopoldomonzani)\
**Post date:** [April 23, 2026, 6:10pm UTC](https://discourse.mcneel.com/t/polyline-joined-with-control-point-curve-breaks-calculation-of-rail/218326/2 "2026-04-23T18:10:31Z")

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Two possible alternatives.

[Track-Polylines\_1.5 a.gh](https://discourse.mcneel.com/uploads/short-url/orir5lxNgzgpGuLW5K4Vn2240CD.gh) (17.9 KB)

 ![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/6/4/6/646e2c16ca1233a86eb33b21a1b1b1e077ca1260.png)

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<div class="post-metadata">

**Author:** ![AA99](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/aa99/32/734371_2.png) [@AA99](https://discourse.mcneel.com/u/AA99)\
**Post date:** [April 23, 2026, 6:35pm UTC](https://discourse.mcneel.com/t/polyline-joined-with-control-point-curve-breaks-calculation-of-rail/218326/3 "2026-04-23T18:35:28Z")

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Thank you for trying. The resulting breps or the half pipes you mentioned still don’t have the fillets between the polyline and the control point curves, which is the main issue.

In my setup, if you try drawing a polyline and then at its endpoint draw a multi-control-point wiggly curve and join them, you’ll see the problem. The fillet at that transition is missing, and it affects the overall result.

Let me know if you see a way around this.

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<div class="post-metadata">

**Author:** ![leopoldomonzani](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/leopoldomonzani/32/637191_2.png) [@leopoldomonzani](https://discourse.mcneel.com/u/leopoldomonzani)\
**Post date:** [April 23, 2026, 6:40pm UTC](https://discourse.mcneel.com/t/polyline-joined-with-control-point-curve-breaks-calculation-of-rail/218326/4 "2026-04-23T18:40:41Z")

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In your definition you have not internalized the curve so it is not possible to see the problem.  
I tried different curves but the result is always correct.

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<div class="post-metadata">

**Author:** ![AA99](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/aa99/32/734371_2.png) [@AA99](https://discourse.mcneel.com/u/AA99)\
**Post date:** [April 23, 2026, 8:39pm UTC](https://discourse.mcneel.com/t/polyline-joined-with-control-point-curve-breaks-calculation-of-rail/218326/5 "2026-04-23T20:39:01Z")

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[Track2.gh](https://discourse.mcneel.com/uploads/short-url/j5HW2nNtcAM6qjoqrtOoziAzdEn.gh) (33.1 KB)

I have internalized a curve within the poly-line

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<div class="post-metadata">

**Author:** ![leopoldomonzani](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/leopoldomonzani/32/637191_2.png) [@leopoldomonzani](https://discourse.mcneel.com/u/leopoldomonzani)\
**Post date:** [April 24, 2026, 7:48am UTC](https://discourse.mcneel.com/t/polyline-joined-with-control-point-curve-breaks-calculation-of-rail/218326/6 "2026-04-24T07:48:09Z")

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I think this is difficult to solve because the radius of the curves is smaller than the size of the offset.  
An example.

 ![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/c/a/7/ca7596f99f8d0af1979b7fb098162e4227147423.jpeg)