Cut surface with breps

[m1988 (m1983)]

I have a collection of breps (walls) i want to get the perimeter/area of the room that the walls are surrounding. To achieve this i have tried to use project and use the projection to cut the surface. I cant get this method to work. Can anyone help me figure this out? Is there any better way to achieve my goal?

cut surface with projection.gh (19.6 KB)

[jessesn (Jessesn Chen)]

@m1988

I have a collection of breps (walls) i want to get the perimeter/area of the room that the walls are surrounding. To achieve this i have tried to use project and use the projection to cut the surface. I cant get this method to work. Can anyone help me figure this out? Is there any better way to achieve my goal?

Please give it a try with Brep|Plane

Grasshopper Online Document

BrepPlane.gh (23.2 KB)

[m1988 (m1983)]

this is not a reliable solution as it is dependent on choosing the correct V from deconstruct brep.. this means that i would have to manually select the correct index in the list item component to get the result i want.

[jessesn (Jessesn Chen)]

@m1988

this is not a reliable solution as it is dependent on choosing the correct V from deconstruct brep.. this means that i would have to manually select the correct index in the list item component to get the result i want.

Another solution based on Project for your reference.

Project.gh (22.6 KB)

[m1988 (m1983)]

i am not able to replicate your result with the file you uploaded. it gives me this shape and a warning at the boundary surfaces component saying “planar surface routine returned no results”

[martinsiegrist]

You can try Mesh Shadow but it might be slow…

[m1988 (m1983)]

@m1988

I tried. It worked on this particular set of walls, but when I tried on another room it did not. Any idea why project doesn’t work? I see no reason why it shouldn’t.

I tried. It worked on this particular set of walls, but when I tried on another room it did not. Any idea why project doesn’t work? I see no reason why it shouldn’t.

[jessesn (Jessesn Chen)]

@m1988

i am not able to replicate your result with the file you uploaded. it gives me this shape and a warning at the boundary surfaces component saying “planar surface routine returned no results”

May I ask which specific version of Rhino you are using? I made it in Rhino 8.26

[JinLong]

Hi @m1988

Can this approach solve the issue?

Please see the picture below.

[jessesn (Jessesn Chen)]

@m1988

I tried. It worked on this particular set of walls, but when I tried on another room it did not. Any idea why project doesn’t work? I see no reason why it shouldn’t.

Please note the walls in the provided model are not fully in touch. You need to use Offset to “correct this issue”. I made a definition based on Mesh Shadow for your reference.

Mesh Shadow Grasshopper Online Document

MeshShadow.gh (22.8 KB)

[René_Corella]

@m1988

Is there any better way to achieve my goal?

Hey @m1988, given the disjointed walls, projection and shadows won’t be very reliable, so a workaround for orthogonal shapes like yours can involve finding (fitting) the right planes to cut and extend your ‘sections’ and determine your outline.

See this example:
cut surface with projection.gh (37.7 KB)

Here’s an example using convex hull → rectangle → Region Union:
cut surface with projection2.gh (25.9 KB)

@m1988

but when I tried on another room

*Note:
The example above fits a plane through each brep, works with ‘simple’ orthogonal objects like these breps.
Maybe you should show us other cases you have so we can test/improve.