How to project and cut out a specific shape on a complex polysurface

Hi everyone!

I’m new to the forum as well as to Rhino itself.
I need help in finding a way to cut out a specific shape on a complex polysurface.
I tried to use the UnrollSrf command, but it seems like the surface is too complex.
Turning it into a mesh didn’t help either.
I also tried "flow along surface command, but when choosing the base surface I wasn’t able to choose the whole polysurface, only a single surface.
Perhaps you will know a better way to do this.
Below you will find my example. I need to project the flat shape B onto the polysurface A in order to cut it out.

Many thanks in advance for any hints!


Hi Lukasz,

Welcome to the Rhino community.
I suggest to check out this page about advanced flattening.

Feel free to ask any additional questions you have. If they are not related, create a new topic for a new question.

Does this help?

Hi @lsztuka,

I’m not sure if flattening is required for what you hope to do with the geometry and that variable will add complexity here. If you just want to trim the polysurface you could use Trim with a curve from a custom Cplane somewhere between Top and Front. You could also use the Project command to project a curve to it and then Rebuild that curve > edit it and finally use Pull to pull it back to the polysrf for a Trim.

I’d also suggest using DupEdge followed by Join to get long curves from the polysrf and use those to make one NetworkSrf unless you need these individual surfaces for some reason. The screenshot looks like the result of making a NURBS polysrf from a polygonal mesh which is generally not useful unless you really need the small surfaces from each face.

If you still need help, post a 3dm file and explain what you want to do with the geometry.

Welcome to Rhino :slight_smile:

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Hi again,

thanks so much for the help to both of you.
Although not at first I finally managed to do what I needed.
First I created the surface from scratch. In order to do that I rebuild the outer edge of shape A.
I then have manually drawn main curves basing on the A surface (on the left of the image).
I used patch surface command choosing all of the curves and edges creating a surface.
I finally used the squish/squish back commands on the created surface.
That worked really well and enabled me to do teh trimming later on.
I’m really glad I was finally able to create this shape.
Thanks again! I hope to be present on the forum more frequently from now on :slight_smile:


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Nice job!

As you found, there is always more than one way to model anything. Another approach would be to take your flat profile curve > use PlanarSrf on it > Rebuild that surface to have more control points > and then edit the ctrl pt rows with the Gumball to get the bend in each direction.