# Automated Way to Achieve \_BlendCrv with G4 Continuity?

**URL:** <https://discourse.mcneel.com/t/automated-way-to-achieve-blendcrv-with-g4-continuity/167877>\
**Category:** Rhino Developer\
**Tags:** windows, blendcrv\
**Created:** [October 25, 2023, 2:44pm UTC](https://discourse.mcneel.com/t/automated-way-to-achieve-blendcrv-with-g4-continuity/167877 "2023-10-25T14:44:36Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![d112](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/d112/32/509475_2.png) [@d112](https://discourse.mcneel.com/u/d112)\
**Post date:** [October 25, 2023, 2:44pm UTC](https://discourse.mcneel.com/t/automated-way-to-achieve-blendcrv-with-g4-continuity/167877/1 "2023-10-25T14:44:36Z")

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Hi,

Grasshopper or RhinoCommon currently do not provide access to **G3** / **G4** continuity as stated here:

[https://discourse.mcneel.com/t/blend-two-curves-with-g3-continuity-in-grasshopper/148656](https://discourse.mcneel.com/t/blend-two-curves-with-g3-continuity-in-grasshopper/148656)

However, I need to blend a lot of curves with G4, which can’t be done manually.

Here are the things I tried, which (I) failed:

1. Trying to reverse-engineer the **G4** blending by distributing 4 control points linearly along the curves tangents at the ends, which are to be blended. The 8 control points are then used in connection with a curve of polynomial degree of 9. This however slightly deviates from Rhinos more sophisticated solution.

The black lines are the curves to be blended, in red the tangents are shown and in green the \_BlendCrv with G4 is shown. The upper curve is a straight line, all 4 control points are on the red tangent. The lower curve is not a line, the 4 control points are not on the tangent.

 ![grafik](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/8/0/6/8069f6c6847fd95b2026e604afe9c1c4a1aa9808.png)

1. Recording a Macro. Usually, you write what you would click in the command-line and enter values accordingly. \_BlendCrv however, uses a popup-window, which leaves the user in the dark how to do things. Is this possible?

Best  
Dan

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**Author:** ![Gijs](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/gijs/32/769882_2.png) [@Gijs](https://discourse.mcneel.com/u/Gijs)\
**Post date:** [October 25, 2023, 2:51pm UTC](https://discourse.mcneel.com/t/automated-way-to-achieve-blendcrv-with-g4-continuity/167877/2 "2023-10-25T14:51:47Z")

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request for G3/G4 is listed as  
[RH-70602](https://mcneel.myjetbrains.com/youtrack/issue/RH-70602) Blend two curves with G3 continuity in Grasshopper

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**Author:** ![dfytz1](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/dfytz1/32/478701_2.png) [@dfytz1](https://discourse.mcneel.com/u/dfytz1)\
**Post date:** [March 15, 2026, 11:38pm UTC](https://discourse.mcneel.com/t/automated-way-to-achieve-blendcrv-with-g4-continuity/167877/3 "2026-03-15T23:38:29Z")

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> [@Blend two curves with G3 continuity in Grasshopper](https://discourse.mcneel.com/t/blend-two-curves-with-g3-continuity-in-grasshopper/148656/7):
>
> I recently made a component exactly for that, it blends up to G4: [G4 blend.gh](https://discourse.mcneel.com/uploads/short-url/dzyImpQJSGLu3ChrmZcyMJaZ3m2.gh) (16.6 KB)

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**Author:** ![brian](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/brian/32/504171_2.png) [@brian](https://discourse.mcneel.com/u/brian)\
**Post date:** [April 7, 2026, 10:13pm UTC](https://discourse.mcneel.com/t/automated-way-to-achieve-blendcrv-with-g4-continuity/167877/4 "2026-04-07T22:13:08Z")

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[RH-70602](https://mcneel.myjetbrains.com/youtrack/issue/RH-70602) is fixed in Rhino [WIP](https://discourse.mcneel.com/t/welcome-to-serengeti/9612)