# How to create this kind of shape?

Hi,

I am quite new to working in 3D with Grasshopper and decided to set a few challenges to myself so I get a better overview of the different tools available (components) and learn how to use them.

As a first exercise I have tried to come up with a shape similar to this piece of furniture by gt2P studio called “Suple”.

From the brief description available on their website I understand that:

• the initial shape is a 3D Convex Hull polygon encompassing several extruded rectangles
• that volume is then digitally smoothed out through subdivision

Here is the diagram provided to illustrate this process:

There is however a few things puzzling me with this information:

1/ The shading on the top right figure seems to indicate that the extruded rectangles (white) span beyond the bounding volume (black) in the Z direction. As if they were passing through it instead of simply being encompassed by it.

2/ The same shading also suggests the presence of a new vertex near the center, between the rectangles. Logically, that point shouldn’t belong to the bounding volume.

3/ There doesn’t seem to be any explanation regarding the transformation of the bounding volume into the shape shown in the bottom left corner. I have tried different strategies to derive such a shape from a convex hull (springs, isocurves, alpha shape) but to no avail.

Questions:

• What steps am I missing ?
• Why the addition of a new vertex near the center and what decides its position ?
• How to derive the final shape (step 3, before subdivision) from the convex hull ?

Would love some help !

Here is the best I could do so far:

Suple test.gh (24.7 KB)

5 posts were split to a new topic: Towers blended on a base

Thank you for the kinds replies.

I’m sorry if my post wasn’t clear, I’m trying to get something that is almost similar to the shape above by sticking to the original process as much as possible . My questions are very specific and relate to the underlying steps that are not clearly addressed in the original description.

If you read it carefully you’ll understand that the rounded shapes you’re mentioning are not curves that have been rounded. These are the holes of a mesh that have been smoothed through multiple subdivisions. In other words they are the byproducts of the routine I’m trying to uncover, not its building blocks.

Don’t be sorry - I’m the one who went off on a different tangent. As I said, meshes scare me because I don’t understand how they work (and frankly I don’t want to), so I probably should have started a different thread. Hopefully someone who is more informed than I will be able to help you.

I’ve moved the posts that did not address the question to a new thread.
-wim

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Looking back at the top right picture, I realize there isn’t one but four new vertices added to the convex hull: 1 at the center (between the rectangles) + 3 near the middle of the 3 naked boundary lines (those that aren’t adjacent to any rectangle).

The center point seems also to be connected to some of the top corners of the (extruded)
rectangles:

Question:

How can I build a polysurface (black) based on the boundary polyline (red) and the selected vertices (blue circles) ?

Suple test 2.gh (34.8 KB)

I’m really surprised by the lack of suggestions/help. I thought this kind of smooth, rounded curvy shape was common and easy to create with Rhino/Grasshopper. Please tell me if something about the way I’m formulating this question isn’t clear.

TLTR. Your initial post and the [not] “brief description” you linked to are verbose and complex. Plus there’s this:

The description in itself (a tiny part of the page I linked) is neither verbose nor complex: It is just 7 lines of text that I have summarized in 2 lines in my initial post. I can even shrink it down further into a single-liner:

• a 3D convex hull that is smoothed out through multiple subdivisions

As you see, the original description is so brief that it ends up being too vague. That is the very reason why I opened this thread: to get some insights regarding a process that is poorly explained. Also, I made sure to provide a diagram to give as much visual information as possible while avoiding being too verbose.

In the same spirit, I made my last question as short and clear as possible: one single sentence with very specific terms (polysurface, polyline, vertices) illustrated by 2 diagrams. Nothing complex about it, I’m sure.

Regarding the plug-ins. Unfortunately, the MeshEdit and Pufferfish components are necessary for the computation of the 3D convex hull and the conversion from a Mesh to a Polysurface. I’ll try to see if I can replace them with a Python script instead. Either way, downloading and installing these 2 components should take around 10 seconds.