Single span corner difficulties

I am currently practicing single spans. In the past I have been aiming for surface continuity with varying results but I just recently learned about the propper aproach. The knowledge I gained at uni was very limited so I would say I am 90% self thaught.

I have a rather (I believe) simple issue. I am trying to achieve a corner that is g2 continous.

However in this approach the Blend Crv doesn’t lie on the surface.
When trimming the corner by either projecting, pulling or spliting with an extruded curve I end up with a horrendous edge.

This results with equally horrendous surfaces.
Edge surf:

I tried a different approach. I made an edge surface using the blended curves rather than the trimmed surface edges and then matched by position but with no good results.

So then I tried using the blended curves as edge curves of the top blend rather than trimming it later. Looks ugly and won’t match propperly.

Only lofting produced half good resuluts but now that I learned about single spans and with my unhealthy perfectionism I can’t let it slide.

Ideally I should be able to set a single span, g2 continous on both ends curve on the surface and use it to trim the surface. I tried SetPt to sculpt the curve to lie perfectly on the surface but with no succes. Is there a way to project a curve and keep the point count and degree the same? Seems unlikely but maybe at least to keep it single span? How should I approach this?

Here is the file if you wouldn’t mind to look at it. It’s messy I know, I just can’t ever make myself to delete anything in any file beacause I might need it later haha. Also don’t mind the layer names, they are in my native language

mebel.3dm (19.8 MB)

Here is a sketch of what I am trying to model for some insight.

Anyways, thank you in advance

Hi Filip - my guess is that one single single span surface can’t match to the surfaces within tolerance. If you want single spans, I think you’ll need at least two, or just insert s few knots (Automatic) to your simple surface.


Thanks so much for the response!
This makes a lot of sense.
In the 2 surfaces approach I am having trouble with matching them with each other, it breaks the the position continuity with the trimmed surfaces.

As for inserting knots. Sadly even with this many knots it won’t match to tolerance. Adding any more knots doesn’t improve tolerance anymore. Is user error possible in this case? Looking at loft results it should be possible with far less knots. I am using multiple edge match surface with g0 continuity, none preserve other end, match edges by closest points and isocurve dir automatic (however I tried the other isocurve dir sdjustments as well). Matching edges spearately also doesn’t help

EDIT: The loft in the first post also doesn’t match to tolerance. I must have checked the rebuild option rather then refit. Refit isn’t good looking at all

Hi Filip - here, inserting a few knots, then metching for position gets me within .006 units


For the single spans, you might need three, I don’t know- that is a fairly twisty edge.
But… why the single spans? As an exercise, or?


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another approach is to over-model the (singlespan) surface and trim afterward:

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Looks great, thanks.

Yup, mainly to exercise. Was never completely happy with my topology. I am trying to learn as much as I can about nurbs. “Mastering” single spans seems like the next step to achieve better surface quality. Also, from my limited experience, less issues appear down the road

Worked beautifully. Thanks a lot

Make sure and watch this video series, it’s an amazing resource that we should all watch a few times.

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