Multi Edge Surface Blend Challenge


I having problems blending between five or more edges of surfaces that have different degree and directions of curvature. The idea is to close a hole not using patch surfaces but a controlled G2 continuity logic. I think it’s quite common problem but I could find any general approach to it. I read about VSR plugin but I would prefer a Rhino native solution.
Thanks in advance

SrfHoleIssue.3dm(148.1 KB)

You’re going to have to break it down into 2 or 3 different surfaces(as I show in my training CD) but the one thing to note is that a mathematically exact solution to where a number of different edges with different radii come together doesn’t actually exist–Patch or not it’ll still be a bit of a looks-good-enough kludge–at least not as you have the problem presented there, there might be a different way of looking at it will result in something that can be resolved using a set of fillet-like blends.

Hi Tom- attached is one way to get at this- all tangent, no g2 blends.(Your existing surfaces and edge trims are all tangent- that being the case, any G2 blends would conflict with that and something would have to give. If the existing transition surfaces were G2 blends, and the trimmed arc (on the plane) were also a G2 blend curve, then you could think about making an all G2 solution)


SrfHoleIssue_PG.3dm(197.5 KB)

Hi Tom,

our plug-in VSR Shape Modeling 2.0 has a function called MultiBlend. This function creates a nice result here without the need to use several functions, or break up the hole into several surfaces. See attached pictures and .3dm:

VSR-Result.3dm(1.2 MB)

If you are interested, you can download a three weeks test version here:

Let me know if you should have further questions.

@JimCarruthers maybe you want to have a look at this, too?



@ Pascal: Thanks for this solution. I followed your instructions and rebuild everything but still wondering if I’ll be able to transfer your concept to the next challenging surface.

The method in VSR (splitting edges in half and generate surface/curves meeting in a kind of centre point) seems similar to the nurbs conversion in Tsplines or Maya and looks like a more general approach. So I thought it must be possible to construct that kind of curves with Grasshopper or within Rhino. But when I just use the curves out of the VSR surfaces I am not able to recreate the same C2 surfaces with Rhino commands!? Do I miss here something?

Hi Tom,

no, you will need our plug-in, the result you see in the 3dm resp. the jpg’s is just the result of the VSR MultiBlend. You select the edges of the hole, and create the surfaces, being able to influence the general shape by the shape slider.

I didn’t try extracting the curves from the MultiBlend, and use them for some Rhino functions. As the surface cluster is a result of really high complex formulas, I’d be surprised if you could create the same surfaces manually with Rhino functions.


I fixed and simplified your topology. I also made all the surface blends G2 this allows for the elimination of the corner round edge. The end result is much cleaner and light on control points.


thanks for picking up the topic again. Looks like a nice approach. When I understand it right: You untrimmed the plane to get rid of one edge, substituted the fillets with g2 blends and closed the 4-edge hole with a network surface!? Thats how I see it but when I do it this way the network surface doesn’t look as clean as in your solution.
Let me know if I miss here something!


I try to avoid using network surf. The 4 hole surface is made from a surface blend, then rebuilt and matched to the input surfaces. I then duplicated that blend edge with a curve and used it to trim the outer planar surface.Then I matched the 1-blend surface to the trimmed edge. Next I used 2 rail sweep to create the 2 sweep surf, using the edge of the 1 blend as the profile. Rebuild UV is essential to fix surface 3. It has to be rebuilt as it’s impossible to get a good blend between a degree 2 and higher degree surfaces.

What I’ve detailed here are techniques I use often on much more difficult topology. You might be able to do this with a solid G2 fillet and the use of trims and split edges.


Here are a couple more solutions.

In the enclosed file the red surfaces show the standard rolling ball solution that mechanical CAD programs would create. I often try to get rid of these pointy fillets. The pink surface is created by bendSrf after first trimming back the two side surfaces with split by isocurve… The extra isocurves in the pink surface are created when you use MatchSrf to make the pink tangent with the middle fillet.

fillet_cornerX.3dm(138.0 KB)

You might try this. Sorry I can’t remember the sequence of commands I used. I just pound away until I get an acceptable result. I believe the key to get good results is to avoid matching surfaces to complex surface trimmed blends.

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