Construct surface from uneven lines

Hello everybody,

I’m fairly new to Rhino and ran into some beginner’s trouble trying to construct a surface from the lines shown in the picture below.


I tried different options but filed to identify one that would lead to a satisfying result. The best fit I managed to get so far is the one shown below. But as you can clearly see there is some unwanted behavior in the areas that are not directly linked to the pink lines I used to construct the surface. I do not want that rippling shown in this image but do not know how to get rid of it either.

Is there an easy way to construct a surface similar to the one shown but without the rippling?
I’m sorry if this is a very basic question but none of the answers I found online or the options I tried really helped me and I’m getting desperate.

Thank you so much in advance!

You can use the command Rebuild to smoothen your curves.

Thank you so much for your very fast reply! I tried rebuilding the pink lines but the result was still as messy as before. I cannot alter the black line as I need its exact geometry later on, eventhough smoothing it out would seem to do the trick.

Is there another way I could achieve a amooth surface without having to alter the geometry of the black line?

Again thanks so much!

It is difficult to say without being able to look at your file.

If your black curve is a polyline with colinear segments, you could eliminate those points with the SimplifyCrv command.

Thanks so much again! I tried your suggestion but I coulnd’t really improve the outcome.

I attached the original file in case you could take a look. (14.5 MB)

It would be helpful to know what this is a surface of. The solution to your problem really depends on that. If you are trying to reproduce the surface of Mars, it would need to be jagged.

It is the geometry of a tectonic fault, the disruption of the rock in the underground along a 3D surface so to say. All I know about this fault is how it presents itself on the surface of the earth (the black line) as viewed from above and the two vertical profile lines (the pink lines). So, ideally I’d like a smooth transition from the first pink line to the second pink line and none of the folded behavior that the surface currently displays. Something like this:

I hope this clarifies things a little. Thank you so much for your input already!

There are two problems I see right away.

First, the Pink lines do not intersect the black line.


Second, Rhino isn’t going to know what to do outside your lines.

Third, your two end curves have a different geometry. One has 7 points and the other has 6.

Thank you so much for the assessment! I was hoping there might be a way around defining a curve at the bottom but it seems to me like there isn’t really if I understand you correctly.

I duplicated the black line and used it as a border at the bottom and tried to create a surface again. The outcome is much nicer than what I got before. I think I should be able to work with the result. So thank you both so much for taking the time to help me out! I attached an image of a part of the surface. In case you see any major red flags I’d be more than grateful for a hint.

Thank you so much again and have a great weekend!

Well the problem is mainly where the top edge curves a lot…

The only way to get a smoother surface is with a compromise on your edge. Then a few more sections to have better control around the tight bends.

Then thank you so much for the overview over my options! I’ll play around a little and see what I can do.