Need help to make 3D hollow circular culvert using Rule package

[bhusalshishir]

I want to make a 3D circular culvert in the city engine using the Rule package. I made a solid 3d circular culvert but I want a hollow 3D circular culvert. So someone please help me to complete this task. How can I do this?

[ThomasFuchs · Accepted solution]

Hello @bhusalshishir 

Here is CGA code that creates a primitiveDisk and then uses the offset operation to hollow it out.
Then the extrude operation gets applied on the annulus to form a culvert. Finally, the setNormals operation is used to set the normals of the inner and outer mantle to soft.

version "2024.1"

@Description("Inner diameter") @Distance @Range(min=0.1, max=5)
attr diameter = 1
@Description("Culvert length") @Distance @Range(min=0.1, max=20)
attr length = 2
@Description("Wall thickness") @Distance @Range(min=0.1, max=1)
attr thickness = 0.1
@Description("Number of subdivisions of the outer mantle")
attr sides = min(128,max(16,floor(8*diameter)*4))

@StartRule
Culvert --> Annulus

Annulus -->
	primitiveDisk(sides, diameter+thickness)
	offset(-thickness)
	comp(f) { border = Extrude}
	
Extrude -->
	extrude (length)
	comp(f) { side = setNormals(soft) Culvert. | all : Culvert. }
	

[bhusalshishir]

Thank you so @ThomasFuchs for your help, it means a lot to me. Thank you for your time and assistance.