and merge edge says edges are merged
notice command line says the edge in the middle is already merged but the edge is thick indicating its a srf border
Hello - surfaces that close on themselves always have a seam edge there - You see this on spheres and torii, etc as well if they are surfaces. As to why - that is the nature of surfaces - they are four-sided and while infinitely flexible, always have a rectangular structure resulting in the four sides, or edges. Where a surface wraps around to close on itself, as a on a cylinder, the two edges that meet form a seam edge - thatâs what you see there in your image.
-Pascal
Hi - in the realm of 3d the term âborderâ is not the same as âedgeâ. Pls learn more about 3d. Thank you.
please teach pascal what you know about 3d.
cuz heâs clearly new at this.
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I donât know why pascal is telling me what and edge is. Cos that was not the question at all.
On the contrary, he gave a very clear answer to your question.
a closed surface has a seam. that seam is comprised of one of the surface edges that is joined to itself.
roll a piece of paper into a tube and tape them together. The two edges that you taped together⌠that is the seam of a closed surface (a tube, torus, sphere, and cone are examples of a closed surface) . the top and bottom of the tube, those are edges as well, but not joined to anything. If you were to, for instance, extrude one of the open edges and join the extrusion and your original tube, you now have a poly surface. (poly = many or more than one)
In rhino we refer to a seam as the join point of a closed surface, Other boundaries are simply referred to as edges.
Please take some time and go thru the lev 1 and lev 2 manuals. They are free and offer a ton of detail about these questions.
It can be confusing when common terms like âEdgeâ and âSeamâ are used very specifically with respect to NURBS terminology.
At first a lot of this seems like unnecessary jargon, but I assure itâs not.
In this case if a Surface has a âSeamâ, it has two opposite edges Joined together, like Kyleâs paper tube example.
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Uh your question was precisely âwhy is this edge here?â
Youâve been told 3 times now that a periodic NURBS surface will still have an edge at the seam where the surface is wrapped around, do you understand that concept yet, Mr. 3D Xpert?
My question was why is this border still here after I merged it. (see comment about command line)
Youâve made a surface that loops around on itself, there must be a seam, doesnât matter if you ask it to âmergeâ or not.
Also there is very little reason to ever use MergeSrf, people do it to try to make a single surface to point-edit and the results are never going to be better than just building one new proper surface for that.
It actually doesnât loop around there are two other seams (borders) on either side. I just want to know if mergeSrf is the correct command to close the seams (borders) if not what would be. Simple as that
Youâll probably have to share your file to get better input. In your screenshot thereâs only the seam in the front visible, along with the top and bottom edges - people will have to guess is to what is going on, and that will not work that well on many cases - like this one.
Why this seams/edges bothers you?
Whatâs the goal you want to achieve?
Edge are in the nature of 3d modeling and most of the time arenât a problem at all.
I really donât understand why the Rhino community cannot give a reasonable answer simply of âhow to close a seam (borders) in Rhinoâ
is it a software that does not have this capability even in 2022?
John Brock has been giving some very helpful direct answers on my other questions. Could he help here?
Is there actually a command that closes a seam? Yes? No?
OK, hereâs a reasonable answer: âYou canâtâ.
People here have tried to explain how NURBS Geometry works and why closed surface seams are part of the inherent structure and cannot be removed, but evidently, you are not really interested in learning that.
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Guys - there are more than ONE Seam on this surface. You are saying that if you have TWO seams on a surface you cant close ONE of them? AT ALL?
not possible to close either one of these two edges with the neighboring surface? once you split a surface - thatâs it? its open FOREVER?
Perhaps some Rhino NURBS terminology is important to list here so we are discussing the same things:
Edge:
Any single segment that is part of a border of a NURBS surface or joined polysurface.
Edge loop:
A closed curve that determines the exterior trim border or an interior hole border of a surface.
Natural edge:
Where the trim edge coincides with the surfaceâs natural border.
Trimmed edge:
Where the natural surface extends beyond the trimmed edge. The part of the underlying surface outside the trimmed edge still exists but is not shown.
Naked edge:
An edge that is not joined to any other edge.
Manifold edge:
An edge that is joined to exactly one other edge.
Non-manifold edge:
An edge that is joined to more than one other edge - structures that are to be avoided, but do happen under certain circumstances.
Seam edge:
Where two edges of the same single surface are joined. The surface is considered âclosedâ in that direction. Example would be an open cylinder surface or sphere. Seam edges cannot be opened (unjoined) or removed.
Singular edge:
Where the edge of a surface has been collapsed to a point. Example, the poles of a sphere or the tip of a cone. Singular edges can be expanded under certain conditions.
Joining surfaces:
If edges of two surfaces are within tolerance the surfaces may be joined. The surfaces retain their original structure but share a common edge which cannot be âremovedâ. They be exploded to return to their original unjoined state (the edges may need to be rebuilt after the explode).
Merging surfaces:
Under certain conditions, coincident untrimmed surface edges of two separate surfaces can be merged together and eliminated, creating one surface. The merge can be smooth (G2 continuous), or not (G1 tangent continuous or G0 position continuous). These last two create surfaces with internal discontinuities that may cause problems later. Merging surfaces is only possible if the internal surface structures are somewhat similar and will change the structure of both.
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I followed the tutorial you posted to get the surface youâre showing here and this is the surface I ended up with:
There are 6 boundary edges (blue) and 1 seam edge (yellow).
The seam can be moved but you canât remove (or merge) it.
I split the surface and joined the 2 resulting surfaces to get what youâve shown in your last post:
There is no seam edge now because there is no closed surface but there are 2 manifold edges where the 2 surfaces join.
You can untrim the surface and get back to the original surface.
-Kevin
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If you have split a smooth continuous surface along an isocurve into two separate untrimmed surfaces, it should be possible to use MergeSrf to transform them back into one single surface. It is not recommended however, as MergeSrf will not necessarily recreate the original structure at the merged edge. It is recommended to keep unsplit copies of surfaces in this case.