# Heavy Blend Srf

**URL:** <https://discourse.mcneel.com/t/heavy-blend-srf/134770>\
**Category:** Rhino\
**Tags:** windows\
**Created:** [December 10, 2021, 2:48pm UTC](https://discourse.mcneel.com/t/heavy-blend-srf/134770 "2021-12-10T14:48:33Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Jonathan\_Hutchinson1](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/jonathan_hutchinson1/32/268934_2.png) [@Jonathan\_Hutchinson1](https://discourse.mcneel.com/u/Jonathan_Hutchinson1)\
**Post date:** [December 10, 2021, 2:48pm UTC](https://discourse.mcneel.com/t/heavy-blend-srf/134770/1 "2021-12-10T14:48:33Z")

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![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/0/5/8/058d547ac0bd16a70b878f3f0eecb8171e105ed2.png)

Why when going from only 5 points to 4 points, does Rhino make such a heavy blend surface? Shouldn’t it be able to generate a solution with around, i don’t know, 7 points that satisfies the requirements at both sides of the blend?

[complex\_blendsrf.3dm](https://discourse.mcneel.com/uploads/short-url/dK61qr1ctybhzMTui367DlCY1fW.3dm) (211.4 KB)

Jon

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**Author:** ![pascal](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/pascal/32/479395_2.png) [@pascal](https://discourse.mcneel.com/u/pascal)\
**Post date:** [December 10, 2021, 3:10pm UTC](https://discourse.mcneel.com/t/heavy-blend-srf/134770/2 "2021-12-10T15:10:29Z")

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Hi Jonathan - you can get cleaner results by

1. `InsertKnot` on the right hand shape \> Automatic in U (so they match)
2. `MakeUniform`

-Pascal

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**Author:** ![davidcockey](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/davidcockey/32/732604_2.png) [@davidcockey](https://discourse.mcneel.com/u/davidcockey)\
**Post date:** [December 10, 2021, 3:16pm UTC](https://discourse.mcneel.com/t/heavy-blend-srf/134770/3 "2021-12-10T15:16:36Z")

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A blend surface can be only 5 control points in the transverse direction, but BlendSrf apparently does not have the logic to do so.

`Loft` between the edges of the surfaces to be blended.  
`ChangeDegree` on the lofted surface. U to degree 5, V stays degree 3.  
`MatchSrf` for curvature on either end of the new surface.  
Result is as below.  
[complex\_blendsrf\_DC01.3dm](https://discourse.mcneel.com/uploads/short-url/rni4tUECW6dy1x9b3LX45WXWkR4.3dm) (1.4 MB)

 ![LoftBlendDC01](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/8/3/6/83655e9cc77e89efe10855a54aef9a96de3f4a4c.jpeg)

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**Author:** ![spb](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/spb/32/635310_2.png) [@spb](https://discourse.mcneel.com/u/spb)\
**Post date:** [December 10, 2021, 5:30pm UTC](https://discourse.mcneel.com/t/heavy-blend-srf/134770/5 "2021-12-10T17:30:28Z")

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After adding a uniform knot to the surface on the right, \_BlendSrf will output a non-Refine version, but the surface is only G0 continuous on each side.

![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/5/e/3/5e352010c8b441449a6e4537a901022e139bde49.png)

[complex\_blendsrf\_NotG1.3dm](https://discourse.mcneel.com/uploads/short-url/sUVXOPto2bdWYJHyEtPn28E2XV3.3dm) (141.1 KB)

If you want alternatives to some of the built-in surfacing commands, please try [My MatchSrf and EdgeSrf](https://discourse.mcneel.com/t/my-matchsrf-and-edgesrf-scripts/132236)

![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/2/c/b/2cb62c4b8b97e08daf6ff86ec4b54f4df9d8f768.png)

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<div class="post-metadata">

**Author:** ![davidcockey](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/davidcockey/32/732604_2.png) [@davidcockey](https://discourse.mcneel.com/u/davidcockey)\
**Post date:** [December 10, 2021, 6:41pm UTC](https://discourse.mcneel.com/t/heavy-blend-srf/134770/6 "2021-12-10T18:41:56Z")

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> [@spb](#):
>
> After adding a uniform knot to the surface on the right, \_BlendSrf will output a non-Refine version, but the surface is only G0 continuous on each side.

Check the “Interior shapes” box in BlendSrf and the results are much better.

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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:** [December 21, 2021, 10:43am UTC](https://discourse.mcneel.com/t/heavy-blend-srf/134770/7 "2021-12-21T10:43:24Z")

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I often prefer to use “Loft” followed by “Match surface” over the “Blend surface” tool for the exact same reason. Also, sometimes “Blend surface” will produce inconsistent flow which is most obvious with the Zebra analysis (no matter if the “Interior shapes” option is active or not). Not sure why “Blend surface” fails so often. It was more robust in Rhino 5, despite that its older version lacked the “Interior shapes” option.

> [@Bugs in Rhino 6 + suggestions for the BlendSrf command](https://discourse.mcneel.com/t/bugs-in-rhino-6-suggestions-for-the-blendsrf-command/63538/11):
>
> Hi Pascal, thank you for taking note on that matter! I see that many people already requested edge align of the “Blend surface” handles years ago. By the way, I misspelled some words in the 1st image from my last post. I just updated the image. slight_smile Hopefully it’s easier to understand now. I will post it here just in case: To clarify. My proposition for the “Divide edge” option is basically a “Rebuild surface U” inside “Blend surface” …

> [@What criteria determines where a variable blend surface ends?](https://discourse.mcneel.com/t/what-criteria-determines-where-a-variable-blend-surface-ends/89291/5):
>
> There is a very easy way to build a perfect G2 blend between those surfaces while matching the surface isocurves. It keeps the control points at minimum and also lets you edit the shape afterwards if History is turned on. In most cases the side edges will adopt the same isocurve direction as the input surfaces. Another advantage of this method is that you don’t necessarily need input surfaces that intersect together (maybe “Blend surface” will implement this kind of blending directly to a surfac…