= "Curve up" modeling =

== Overview ==

"Curve up" modeling refers to creating construction curves that define shapes, then use tools to create surfaces from the curves.

Another way of modeling is ["box up" modeling|box_up_modeling], where you start with a basic shape such as a polygonal [box|/shelf/box] or [sphere|/shelf/sphere] and then add, extrude, modify, cut, delete, smooth, etc. polygons to build up the shape you want.

Curve up modeling is often associated with NURBS modeling, and box up modeling with polygons. However, Houdini can create polygonal geometry using the tools listed below.

See the [Model tab|/shelf/model] on the shelf for more modeling tools.

== Tools ==

Create curves:
    [Curve|/shelf/curve] tool on the *Create* shelf tab. This tool creates a [Curve node|Node:sop/curve].

Create a surface from profile curves:
    [Loft|/shelf/loft] tool on the *Model* shelf tab. This tool creates a [Skin node|Node:sop/skin].
    
Create a surface from a mesh of U and V profile curves:
    [Skin|/shelf/skin] tool on the *Model* shelf tab. This tool creates a [Skin node|Node:sop/skin].
    
Create a surface from profile curves and rail curves:
    [Rails|/shelf/rails] tool on the *Model* shelf tab. This tool creates a [Rails node|Node:sop/rails].
    
Sweep a profile curve along a rail curve:
    [Sweep|/shelf/sweep] tool on the *Model* shelf tab. This tool creates a [Sweep node|Node:sop/sweep].