From movies to print ads, a variety of media uses 3D models. The techniques for rendering them varies depending on the nature of the model. Creating smooth curves in 3D models is vital when you are trying to fashion organic looking models of people, animals or plants. This is especially true of people and animals, since they need smooth curvy joints in order to bend naturally. There are several points to consider when trying to create such figures.
1. When using a modeling program to create a curvy, organic shape, it is important to have a photograph or sketch of the figure you want to create to load into the modeling program as a reference. For example, if you are using the box modeling technique, having background images allows you to judge how far to extrude a polygon or move an edge. In most 3D modeling programs the images can be brought in either by applying them to pre-existing grids or by applying them as textures to plane primitives.
2. Another important aspect of creating curvy 3D models, specifically models that will have to bend, is to make sure that
they can bend properly. For example, a 3D model of a human will have to be able to bend at the elbow, knees and other points. If the model doesn't have enough geometry (polygon faces) at that point, then it will bend unnaturally with hard edges rather than curves. To ensure that the joints work properly, modelers will often, after modeling the overall figure, return to these joints and add extra geometry with tools like "Tessellation" or "Edge Extrude."
3. Even the most diligent modeler will usually find that his model will appear a bit blocky when finished. The answer to this problem is more geometry. Rather than trying to add more polygons directly, most 3D modeling programs now provide an automatic smoothing function that when applied to your whole model adds more polygons and makes the entire surface smoother. Usually this process is adjustable so that you can set the amount of the smoothing. You want to apply enough smoothing that the model looks curvy and smooth, but not so much that your render engine will be slowed down when rendering.