3D circle, ring, round line

[dimvolk]

Hi
My problem is how create 3D curve line, ring, circle line etc... (not cilinder, disc). For example i need create scene/house with one of walls is concave/cambered (oval/round). In examples and wiki all objects is with straight lines. I can't find any example how create semicircle line, box or cube with round one of sides, etc.
Maybe i need use objects deformation?
What should I use for this? Any help

[EgonOlsen]

Every object has to be created out of triangles. If you want found edges, you have to approximate them by using triangles. It might be the best solution to create them in done 3D modeling application and then export them as obj files.