Polygons, NURBS and Sub-Divisions

Polygon, NURBS and Sub-Division surfaces have different characteristics and require different techniques to manipulate and model each type. Surfaces become the forms of the subjects that one intends to depict through modelling. These surfaces are all comprised of faces and vertices. Different modelling programs may have different terms for these elements but they are essentially the same. Textures can be applied to these surfaces that can make them appear more naturalistic or realistic to the viewer so that it is more believable. There are certain advantages and disadvantages while using certain techniques on each surface. The following covers what these are through Maya.

Polygons
A polygon surface is comprised of faces that are flat surfaces that form into shapes. These faces are connected together by a poly mesh. This is a grid of edges that connect each face together. Each face is completely flat therefore the angle of each face to another is what determines the form of the surface.

Polygon Modelling
By creating a polygon primitive one has a basis to model from. The polygon shape might not have enough subdivisions so one can model it with more detail. Therefore one can subdivide it so that it consists of more polygons faces. To model the polygon one can select the vertices or faces and move them with the move or scale tools. By selecting the arrows on the tool one can model a form in the X Y Z axis’s. If one desire’s to model in a more symmetrical manner without having to split the form in half and duplicating it in symmetry, one can use the scale tool. By selecting vertices or faces on opposite sides of the form one can model a polygon in a symmetrical manner. If the polygon mesh is not in order and the surface of the polygon is not smooth one can use the smooth tool to smoothen the surface and organise the polygon mesh. Polygons can be split in half with the split polygon tool that allows one to create more faces on a certain area. If one wishes to make an extension from the form of the polygon one can select a polygon face and select ‘extrude’. This allows one to pull another face from the surface to create an extension.

Advantages
Polygons can be used to create rounded or hard-edged forms depending on how sub divided the poly mesh is and the amount of faces it has. They are the best surface to use for video games because they use the least amount of data (Maya PLE) and therefore allow greater performance from a system.

Disadvantages
Forms may appear blocky and don’t easily appear as smooth as do NURBS without having many polygon faces. One also cannot create smooth and organic appearing surfaces as easily as one can with NURBS.

NURBS
This abbreviation stands for ‘Non-Uniform Rational B-Splines’. NURBS use a method of mathematically describing curves and surfaces that are well suited to 3D applications (Maya PLE). NURBS surfaces are created from curves that determine the form of the subject that one intends to create.

NURBS Modelling
Though one can start modelling from a primitive NURB can also create a one from using a control vertices curve tool. With this a curve can be created that defines the form of the NURB. By selecting the revolve option the round from of the NURB is created. By moving the control vertices the whole form of the NURB is changed as if one is working with clay on a spinning wheel. This technique is suitable for round objects such as plates, cups and vases. One can also model from NURBS primitives. By selecting the control vertices of the primitive one can move and scale them to bend the curves of the NURBS surface and change it’s shape.

Advantages
NURBS are suitable for designs in motorcar and engineering industries because of the smooth appearance of the forms and still use less data (Maya PLE). The Curves used to create NURBS can also be used to create motion paths that lead movement in an animation.

Disadvantages
It’s not as easy to use NURBS to create flat and sharp edged objects as it is with polygons.

Sub-Divisions
This kind of surface holds the characteristics of both NURBS and polygons including it’s own that the other surfaces do not. The level of detail of the form that is displayed can be changed without affecting the result of the final rendered image or animation.

Sub-Division modelling
By creating a sub-Division primitive one can model the surface with control vertices with the same complexity as one can with polygons with the rounded appearance of NURBS. One can also switch between levels of detail, which reveals more control vertices ands allow one to model with more sensitivity. If one selects polygon proxy mode, a polygon box will surround the Sub-Division. This box will not show on the final render but allows one to model the general shape of the Sub-Division with the Polygon’s faces and vertices. If one extrudes a face of the Polygon, a part of the Sub-Division will be extruded with it.

Advantages

One can work with Sub-Divisions in a similar manner that one can with Polygons and NURBS. This kind of surface is easier to use to create organic forms and also be shaped with fewer vertices. One can build up form from one primitive instead of stitching primitives together where on has to with NURBS.

Disadvantages
Working in higher levels requires a lot of performance from the hardware of a computer.

References:

Maya PLE Tutorials