Modeling/surface strategy

Once again I have to reach out to all intelligent people for intelligent advice! I’ve been struggling with different ways to connect/merge these surfaces in a smooth way but always ends up with a sharp corner/triangle somewhere (the open gap in the middle) I must be thinking wrong… Any clever takes on this?

srf_hoffster.3dm (236.8 KB)

Hm - it looks to me like that tricky area is not quite defined as a design - you’re trying to think of how to resolve all of that but things do not seem to line up, quite - it is certainly possible to monkey around and get some surfaces in there but I wonder what the intent is here:

The edges of the green and black surfaces look (to me) like they might be comfortable falling on the angled near-plane (blue) but they are higher - so that leaves a complicated thing happening as you try to hook things up with the fillet that is on the edge of that blue plane… I think it would all be happier if it all lined up on the plane.



Real problem is that the green surface is tangent to the purple yet blue is position and has opposite side peak so the surface you aim to achive has to be at least two position contuniuty corner which is what you decribed as your problem.

as you can see there is a little sharp area in my attempt.

srf_hoffster5_blastered.3dm (130.4 KB)

I am not sure but it could be fine…
srf_hoffster2.3dm (408.9 KB)

Hi, @anton.hoffman
In general there are endless solutions, some of them require changing the modeling methodology; while in other methods it is decided to continue preserving the initial surfaces and try to repair them in several stages.
in my case I went the short way, since you ask for an alternate method to solve your problem; Here I present a different approach.

In this case; I take the surfaces to the curved surface, I recreate the curved surface in one piece by means of Sweep2 and make a cut using a pipe to then use BlendSrf

srf_hoffster1.3dm (708.4 KB)

As Pascal Golay noted above, your larger horizontal rounded edge on the left side is lower than the right one, so this will inevitable make the final shape somewhat uneven. The green surface edge on Pascal’s image should be lower in order to guarantee a smoother flow of the large blend surface that’s missing on your model.

I had to fix some of the adjacent surfaces to make them match in a more G2 way. One thing to remember in such projects is that first you have to deal with the larger rounded edges (or blend surfaces), leaving the smaller ones for the last stage of the modeling.

Anyway, here is my take on this, while trying to preserve your both rounded edges.
srf_hoffster1 BG.3dm (381.7 KB)

You’re absolutely right - this is a somewhat sketchy cad and I try to understand the surfaces and different ways to solve it (as I couldn’t really understand everything just on paper). But this is all great tips! I’ll try to line it up better in the next round! Thanks!

Thanks @Blastered

Great attempt tho! I think what I mainly missed to work with is the highlighted area below. That helps a lot.

I’ll take a closer look at this approach and see how the little sharp thing could be avoided!

Yeah, exactly, I guess there are plenty of ways to approach this design and I really appreciate to see other ways to think about it! This actually looks pretty nice, but I’ve always been thinking that I should try to try to avoid the sharp triangle that this creates. But it doesn’t’ seem to create a big issue (surface quality wise) here. I’ll play around with this approach as well!

Super excited to see this! Can you save as Rhino 6, you think? :smiley:

Noted! This is a great insight for me, as @pascal also high lighted, and I’ll bring that with me. I’m also impressed by the surface quality you managed to achieve with your new surfaces. I was personally afraid of (as in trying to avoid) an intersection like this but you’ve proved me wrong - this looks smooth

That transition is relatively smooth, because I matched the split surface’s left edge to the adjacent surface with G1 and then used the “UVW move” tool to manually edit the control points of the 3rd control point row to make the transition appear almost like G2.

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That’s great - thanks!

Hi all (again!) I’d like to pick up this old thread with a similar issue, as the geometry is somewhat similar. We found several great solutions last time, and also tips and tricks about how to simplify things.

This time, I thought it would be much easier as the geometry is less complex. But I can’t really figure out how to solve it the best way, as I end up in similar problem no matter how I do it.

So, firstly - the visual result I’m after is this: The sharp edge (blue) shall disappear smoothly as it merges into the blended surface (red)

The file looks like this:

[Yellow] is where the blended (curvature) surface shall go up to, and the [red] is the curvatue used for splitting the “flat” surface. Like this:

Now, my problem begins. As shown above I have created the first blended surface (grey) and also the 2nd one to the right. The flat bottom goes out to infinity, a sharp edge, to bind the grey surfaces together. My issue is, that no matter how I try to build this surface, I end up in, if I exaggerate this image, in a situation where they don’t match up:

I do understand, since the bottom surface goes all the way, that mathematically the blend tool tries to keep curvature all the way. Even though the surface is almost invisible. And therefore create a surface like this.

But when I try to build it manually instead, with a set of support curves along the way, and skip curvature at the end, I end up in flimsy surfaces with creases and bumps. Am I missing something obvious here? How can I make this sharp edge to fade out nicely?

models_hoffster.3dm (227.6 KB)

Hello - is it the intention that the upper curve (bump-straight-bump) fade to a somewhat smoother one on the deck

Or should these be similar, one way or the other?


Smooth surfaces start with smooth curves. The red and yellow polycurves are messy and need to be rebuilt.

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Once you get curves that are clean and how you like them, one strategy that may work is to great a curve that is G2 to the suface edge at the point where you are willing for the surface to begin fading to a sharp crease (if I get your intention)

The red curve here:

it has been matched to the edge using Match > SurfaceEdge, then compressed at one end with EndBulge. I also made the line (green) match the point arrangement of the red curve so that a sweep:

has a reasonable chance of the isocurves being not too wavy. The left half should be pretty smooth to the deck surface and face away from that to the right.
But none of this will look any good, I think, with the top and bottom rails as you have them in the file.


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Hi, thanks for the feedback! Yeah, the yellow (upper) curve looks like intended. Would a more similar curvature help on the bumps help in creating the surface you think?

@davidcockey @pascal The red curve is a somewhat quick offset-and-scale curve show what I intend to do and I know it’s messy here, but I don’t really understand what is messy with the yellow one - could you elaborate on that? I’ve tried to create them as simple as possible but still being able to meet the design intention.

Hi again, just wanted to follow-up my comment above. @davidcockey @pascal I can try to minimic the design intention with one blend crv like below: (example to the right compared to org. to the left). Is this something similar to what you are thinking about? I have a hard time seeing how I could simplify it more without loosing the shape?

It depends on what your design intent is. The reworked curves individually look reasonable. A surface defined by them will have some bumps. If that is the design intent then the curves are good.

Start by not working about the transition and create a simple surface between the curves. Decide if that surface is satisfactory. If not modify the curves and create another surface. Experiement. Work on the surface with the transition after you have an acceptable surface without the transition.

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