Creating a virtual world requires designing, making and placing the objects, scenes and environments which make up the world- this is referred to as modeling. (Kerlow, 77, 2000)
In digital 3D animation, one is confronted with the issue of choosing the right modeling techniques to mould and create different objects. These techniques consist of polygons, NURBS and/ or sub-divisions and each technique holds their various advantages and disadvantages. Any technique used is determined by either personal preference, the type of model (organic, cornered or hard edged), the methods properties and the type of rendering and output. (2006, AICT)
The most widely used and traditional technique used in modeling is polygon modeling. The term ‘polygon’ has roots in Greek, meaning “with many angles”. (Kerlow, 83, 2000) Polygons are made up of points that connect edges which make up leveled surfaces. An example of this would be the simplest form of a polygon is a triangle, as it consists of points connecting edges and therefore creating closed planes. Polygons are very useful in modeling, especially many polygons are composed together to form one polygon mesh. This mesh forms a certain patchwork that can be used to extrude polygons, mould and form a versatile amount of objects.
There are many advantages of using polygons to model and object. Firstly, due to their straight faces and edges, polygons are usually used for modeling shapes with sharp edges or corners. However, this does not limit the polygons potential. With the use of blending, moving, twisting, the polygon mesh is actually quite versatile in its modeling ability. Even though its edges limit smooth curves, its ability to extrude, bevel and weld itself and other polygons together makes it an easy fast method to choose.
The disadvantages of polygons are its hard edged, leveled components that does not allow for curved surfaces. Organic modeling is limited in potential as more polygons must be added to create such models and even then there are no accurate smooth curves and surfaces. Another problem is the complex structure and geometry that make up and object affects the flow of work as more compensation is needed by the software to render and deal with the amounts of polygons. Rendering time and general work time is reduced.
Nonuniform Rational B-Spline (NURBS) modeling are more advanced splines. Splines (sometimes called curves) are line segments that are supple and are made up of vertices. (Ratner, 1, 2003) They are usually limited in their ability to be cut or transferred. This brings in NURBS which are basically splines that consist of a small amount of points and allow for cutting, pasting and they are highly mathematical constructs. They can be altered without changing the original properties. (Lewis, 217, 2004) NURBS are mostly used for organic modeling and complex modeling. With polygons, creating a curved surface causes a low resolution appearance and render, whereas creating a curved surface with NURBS gives an almost clean curved surface. NURBS use surfaces and curves to create a 3D object. They contain a variation of weights and knots, which allow for easy manipulation of the curve. When the weights are equal, the curve is non-rational, but when the points are maneuvered and adjusted and form different weight variations, the curve becomes rational. (Kerlow, 105, 2000) They are not render-able but their surfaces are. (Autodesk Softimage, 2010)
NURBS have many advantages when it comes to modeling. Complex and difficult objects are handled well by NURBS due to its flexible nature. There is an excellent amount of control that the NURBS allow due to the fact that they don’t change the original properties when altered (such as cut). NURBS make up a small amount of data which then helps with work time and rendering time as the information is not too much for the computer and software to process. NURBS are of higher resolution that polygon curves are as they do not contain so much data to be handled and processed. The storage of information by NURBS and the type of information withstands the growth of technology and will not become redundant for the next decade or two. (McNeel, 2010)
The disadvantages of NURBS are that the shared points must be sealed to prevent gaps. The surface may split along the seam, which causes gaping holes to surface. When one manipulates the weights and knots of the NURBS, the rendering time is lengthened. Rational curves may cause systems to disregard certain information when transferring the data. (Kerlow, 105, 2000)
To create a connection for polygons and NURBS and to eliminate the disadvantages of the two, a new type of modeling is used, namely subdivision surface modeling. This modeling is mostly used for organic modeling but can be used for other types of objects. Subdivision surface modeling makes the computer fill in the interior or the model, eliminating the holes that form in polygon and NURBS modeling. Here, no NURBS are used and so there is no worry about split seams. (Avgerakis, 246, 2004)
The disadvantage of subdivision surface modeling is the limited use of texturing the object. Mapping with UV techniques becomes difficult unless the texture coordinates are subdivided like the coordinates of the model. (Kerlow, 131, 2000)
Although there are many types of modeling available, each one eventually uses polygon meshes. (Avgerakis, 246, 2004) Each technique has its various advantages and disadvantages and using these methods will involve an encounter with such advantages and disadvantages as well as the type of object and the personal preference of the modeler.
Bibliography
· Avgerakis, G. Digital animation bible: creating professional animation with 3ds Max, Lightwave and Maya. McGraw- Hill Companies Inc. 2004.
- Kerlow, I, V. The Art of 3-D Computer Animation and Imaging. John Wiley & Sons, Inc. 2nd Ed. 2000.
· Lewis, G. Lammers, J. Maya 5 fundamentals, Volume 1. New Riders Publishing. 2004.
- Mcneel. NURBS modeling for Windows. Rhinoceros website, Updated 2007. http://www.rhino3d.com/nurbs.html
- Ratner, P. 3-D Human Modeling and Animation. John Wiley & Sons, Inc. 2nd Ed. 2003.
- Unknown (AICT). General Modeling Methods, Updated August 23, 2006 http://www.ualberta.ca/CNS/RESEARCH/Vis/3DModeling/methods.html
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