# How to solve this kind ok surface continuity situations?

I want surface 1 to change, surface 2 should remain in position. Surface 1 should match both surface 2 and 3.
Surface 1 and 3 should be calculated based on “average point”. Surface 2 should remain the same (position).
If I do a matchsrf and select the edge of surface 1 to match surface 2… but this will change also the edge between surface 1 and 3 making this side not match.

Here’s the 3dm
srf.3dm (127.5 KB)

hello,

if you can send this file a lot of people could help you

Just turn on the control points of (1) and (3) and arrange the coinciding control points of each surface’s edge and their immediate neighboring control points to lie in a straight line perpendicular to the edge. That will ensure tangential continuity. If you want curvature continuity do the same with the next neighboring control points as well.

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That works as long as zero curvature is satisfactory. If curvature continuity is needed but not zero curvature then the control points will not be in a straight line.

Do you mind elaborating that?

Why would you want a non-zero curvature between two surfaces? I don’t claim to be nurbs expert but I don’t think I understand what you mean. What case you have in mind?

Hello - three points in a line results in zero curvature at the end of a curve - that is only sometimes what is needed but it does ensure continuity with a curve that has the same condition at the end.

-Pascal

If it was mine project, I would make sure that the end surfaces at either side are carefully shaped so that they form a visually smooth flow to each other, before I go with the middle surface that blends between them.

You may want to start with something like that. Not ideal, but just showing one of the possibilities. I made the surface by using “Sweep 2 rails” and further optimized the shape by reducing the control point count with “Rebuild surface” and then “Move UVW”. Then I applied “Match surface” a few times to each corner.

srf.3dm (925.0 KB)

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The result is perfect but I don’t completely understand / can’t reproduce this workflow. I made all the surfaces with sweep2 too, what’s the purpose of using MoveUVN here? I mean… what do I have to achieve/ move with it?
About Match surface you used multiple between 1 2 and 3 or single “mode” between 1 - 2?
Why is “surface #1” a trimmed one in your case? When did you trim it?

Tried to smooth out the seam as much as possible…I basically rebuild part of your geometry using sweep2 and then mirror it to match the surface, not sure if its good enoughsrf.3dm (348.7 KB)

I had to trim your starting surface (the thin one on the right corner) so that its edge is nearly vertical, in order to provide better flow for the eventual match of the blend surface. The other reason to trim that surface was to open more room for a smoother transition between it and surface #1.

As for the “Move UVN” tool, it’s used to manually adjust the control points of the surface to alter it’s shape according to your preference while using Zebra analysis as a guide to achieve smoother possible reflections.