Components of a mesh

There are three basic components that we use in polygonal modeling:

• Vertices: The most basic piece of geometry is a vertex (the plural form is vertices). A vertex is a single point in 3D space. It has no size nor orientation; it only has a location within the mesh object. You can't do much with vertices alone, which is why we need edges. 
• Edges: These are straight lines that are drawn between vertices, similar to a connect-the-dots puzzle. The edges that connect two points are always perfectly straight in polygonal modeling.
• Faces: The visible part of a polygon. Faces are created by filling in the space between three or more edges.

The following diagram shows the vertices, edges, and faces of a 3D model:

Polygons can have any number of sides; three sides make up a triangle (tri), while four sides make up a quadrilateral (quad). There are lots of fancy names for specific polygons with more than four sides, such as pentagon, hexagon, and so on, but in the world of 3D modeling, any polygon with more than four sides is simply referred to as an n-gon. The following image shows some of the basic polygons you'll come across:

The way in which these components are connected is referred to as topology, a subject that we will cover in depth later in this book. There are many best practices and rules for creating a mesh with good topology. The most basic rule of topology is that quadrilaterals are the best type of polygon, triangles should be used sparingly, and n-gons should be avoided altogether. Models that don't follow the rules of good topology usually have problems in the final result. Topology is a very large and advanced subject, so we won't go into any more detail about it in this chapter.