Polygonal modeling

Polygonal modeling is well suited to scanline rendering and is therefore the method of choice for real-time computer graphics.

Surface normals are useful for determining light transport in ray tracing, and are a key component of the popular Phong shading model.

In many systems only one of these normals is considered valid – the other side of the polygon is referred to as a backface, and can be made visible or invisible depending on the programmer’s desires.

Many modeling programs do not strictly enforce geometric theory; for example, it is possible for two vertices to have two distinct edges connecting them, occupying exactly the same spatial location.

In order for a mesh to appear attractive when rendered, it is desirable that it be non-self-intersecting, meaning that no edge passes through a polygon.

In this method, the user creates a 2D shape which traces the outline of an object from a photograph or a drawing.

In general, the artist will model half of the head and then duplicate the vertices, invert their location relative to some plane, and connect the two pieces together.

Common primitives include: Finally, some specialized methods of constructing high or low detail meshes exist.

These devices are very expensive, and are generally only used by researchers and industry professionals but can generate high accuracy sub-millimetric digital representations.

In scanline conversion, each polygon must be converted and displayed, regardless of size, and there are frequently a large number of models on the screen at any given time.

Often, programmers must use multiple models at varying levels of detail to represent the same object in order to cut down on the number of polygons being rendered.