# G2 matching problem

**URL:** <https://discourse.mcneel.com/t/g2-matching-problem/208900>\
**Category:** Rhino\
**Tags:** mac\
**Created:** [August 25, 2025, 3:17pm UTC](https://discourse.mcneel.com/t/g2-matching-problem/208900 "2025-08-25T15:17:02Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Lagom](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/lagom/32/767418_2.png) [@Lagom](https://discourse.mcneel.com/u/Lagom)\
**Post date:** [August 25, 2025, 3:17pm UTC](https://discourse.mcneel.com/t/g2-matching-problem/208900/1 "2025-08-25T15:17:02Z")

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Very basic fading edge patch layout; matching G2 lengthwise, with the “Preserve isocurve direction” option on, nevertheless sees the matched surfaces jump off their long edges, and G0 continuity is lost. The exact same surfaces aligned G2 in Alias (IGS export) remain G0 continuous, keep to their edges. Why is this?

Matching G1, with the “Preserve isocurve direction” option on, and some time consuming CP noodling (that should not be necessary) does work.

 ![Skärmbild 2025-08-25 16.50.31](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/0/7/c/07c917e9aa8317ea48e11d947102ba623c2dfa4b.jpeg)  
[G2 matching problem.3dm](https://discourse.mcneel.com/uploads/short-url/qxtoSD0JcTuWLmdlndP43tKhFlD.3dm) (105.9 KB)

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<div class="post-metadata">

**Author:** ![Lagom](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/lagom/32/767418_2.png) [@Lagom](https://discourse.mcneel.com/u/Lagom)\
**Post date:** [August 25, 2025, 3:19pm UTC](https://discourse.mcneel.com/t/g2-matching-problem/208900/2 "2025-08-25T15:19:12Z")

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Apparently, [this is a 12 years old bug](https://discourse.mcneel.com/t/bug-matchsrf-fails-to-maintain-isocurve-direction-cp-flow/147004) 😬

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**Author:** ![theoutside](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/theoutside/32/770924_2.png) [@theoutside](https://discourse.mcneel.com/u/theoutside)\
**Post date:** [August 25, 2025, 10:34pm UTC](https://discourse.mcneel.com/t/g2-matching-problem/208900/3 "2025-08-25T22:34:56Z")

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Hopefully @menno gets to work on matchsrf in the near future.

it needs a lot of love.

fwiw, patch in v9 may be the best tool in Rhino to do this type of work going forward.

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**Author:** ![theoutside](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/theoutside/32/770924_2.png) [@theoutside](https://discourse.mcneel.com/u/theoutside)\
**Post date:** [August 25, 2025, 10:36pm UTC](https://discourse.mcneel.com/t/g2-matching-problem/208900/4 "2025-08-25T22:36:53Z")

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fwiw in the level 2 manual there are 2 lessons for making fading creases that do actually work with matchsrf in its current state. not arguing this is better than what alias has, but it’s worth taking a look at.

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**Author:** ![Rhino\_Bulgaria](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/rhino_bulgaria/32/505284_2.png) [@Rhino\_Bulgaria](https://discourse.mcneel.com/u/Rhino_Bulgaria)\
**Post date:** [August 26, 2025, 4:59am UTC](https://discourse.mcneel.com/t/g2-matching-problem/208900/5 "2025-08-26T04:59:29Z")

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This has been requested gazillion times during the years… The two most important NURBS modeling tools, “Blend surface” and “Match surface”, both saw just a minor love since Rhino 4 (released in February 2007). If memory serves me right, Rhino 4 added the ability to rotate the individual handles of the blend surface. That was the last major feature added to these tools.  
Rhino 5, Rhino 6, Rhino 7, and Rhino 8 focused on other tools. If Rhino 9 also doesn’t fix that bug, that will make more than 3 decades of ignoring it. 🙃

> [@Wish: "Match surface" to preserve the flow of control points](https://discourse.mcneel.com/t/wish-match-surface-to-preserve-the-flow-of-control-points/102236):
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> I wondered if the “Match surface” command could be upgraded to apply G1 or G2 to the general shape of a surface, while preserving the flow of its control points. The current implementation with curvature match (G2) forces the 3rd row of control points to follow the direction of the 2nd row. However, in many situations this will destroy the ideal shape of a surface. For example, Alias could apply curvature match that only adjusts the control points of the matched surface only in the normal direct…

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<div class="post-metadata">

**Author:** ![Lagom](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/lagom/32/767418_2.png) [@Lagom](https://discourse.mcneel.com/u/Lagom)\
**Post date:** [August 26, 2025, 5:53am UTC](https://discourse.mcneel.com/t/g2-matching-problem/208900/6 "2025-08-26T05:53:16Z")

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> [@Rhino\_Bulgaria](#):
>
> Rhino 5, Rhino 6, Rhino 7, and Rhino 8 focused on other tools.

That’s the problem with the “Swiss Army knife” approach to product development. The “Preserve isocurve direction” option is so very essential and should just work.