Split one mesh using another as the knife

Split one mesh using another as the knife

I have a plane that intersects a closed polygon mesh.

How do I cut the plane so that the portion INSIDE the mesh is separated from the part that is outside?

This stuff is all so abundantly simple to do in Rhino3D, but here I am flailing.

tone

DulcetTone said:

I have a plane that intersects a closed polygon mesh.

How do I cut the plane so that the portion INSIDE the mesh is separated from the part that is outside?

This stuff is all so abundantly simple to do in Rhino3D, but here I am flailing.

tone

Click to expand...

Hi Dulcet, do you have an screenshot or better the C3d file that you are working on? It may help understand what you are trying to do.

Rhino is a NURBS app and C3d is a subdivision app. So they work in different ways. There are methods to get what you want done most likely. Unfortunately booleans aren't as clean to use in subdivision modeling as they are in a NURBS app.

Swizl said:

Hi Dulcet, do you have an screenshot or better the C3d file that you are working on? It may help understand what you are trying to do.

Rhino is a NURBS app and C3d is a subdivision app. So they work in different ways. There are methods to get what you want done most likely. Unfortunately booleans aren't as clean to use in subdivision modeling as they are in a NURBS app.

Click to expand...

I could send a file, but it is large. Imagine a house being cut through by a plane that is 50 miles long on each side (well, a plane large enough that no edge of it is within the house). I want to cut the plane so that the portion within the house becomes a wall of the house. I would delete the other part.

tone

DulcetTone said:

I could send a file, but it is large. Imagine a house being cut through by a plane that is 50 miles long on each side (well, a plane large enough that no edge of it is within the house). I want to cut the plane so that the portion within the house becomes a wall of the house. I would delete the other part.

tone

Click to expand...

Ah ok, one way I've done something like that when I want a cut away view is to use a cube and then use a boolean. It may work better that way anyway as it's non-destructive and you can adjust it later if you want. The only problem is that if your mesh is complicated it may look jacked up. You'll have to clean up the mesh for the house and make sure that all the polygons are part of one object. It's better if your object is water tight with all polygons connected and optimized. I'm attaching a VERY simple house as an example. Sorry there isn't a push a button to make it work.

Someone else may have some better ideas than me. I've used this method to do some cut away views on some metal extrusions before, but that's a lot less complicated than a building.

You can use a boolean modifier / creator which even lets you animate the cut but it relies on the mesh being cut being topologically sound and a single mesh (which itself could be booleaned together, but that causes texturing issues if you aren't careful). The odds it will all work flawlessly fly towards zero as the meshes get more complex, and especially when the meshes have coplanar faces.