Self-Developing a MUVE for Research and Educational Innovations - Teaching through Multi-User Virtual Environments - page 456

There are three main ways of modeling: poly-
gon, NURBs (non-uniform rational B-spline),
and sub-d (sub-division). We will concentrate on
polygon modeling because it is the most natural
one to learn — as it is based on geometric primi-
tives and familiar operations — and it is also the
one most commonly used in commercial video
games. With polygon modeling, one models an
object by adding, deleting, and moving vertices,
edges, and faces. The drawback to polygon
modeling is that it results in models with sharp
boundaries. However, most modeling packages
include automatic smoothing operators to round
off sharp points and edges.

two new vertices. After you make one or more
cuts, you can move or delete any of the elements
that result from your cuts.
The extrude technique. The final basic way
a polygon modeler creates variations is by extrud-
ing polygon faces. Extruding takes a face and
raises or lowers that face while automatically
adding the faces needed to support the raised or
lowered face. Figure 4 depicts two examples of
extruding a face.

Application of the Basic modeling
Techniques to Creating a Virtual
World

Basic Polygon modeling Techniques By starting with basic primitives like boxes and

planes, and then modifying these primitives using
the four basic polygon-modeling techniques of
moving, removing, cutting, and extruding, you
can create the exterior of a basic virtual world
consisting of a terrain, a sky, roads, sidewalks,
and buildings. We will also paint the faces of the
objects in our virtual world using colors that are
available in all modeling programs.
Preparatory Step: Selecting a Unit System.
Before you start creating a virtual world, you
should decide on a unit system. If your modeling
program does not support US Standard or Metric
units, you can adopt the convention that one unit
= one foot. So, for example, if you want to create
a square building that is 50-feet wide, 100-feet
long, and 200-feet tall, you would start by adding
a box primitive that is 50x100x200 units.
Step 1. Modeling the Terrain. In creating a
virtual world, your first step is to decide how big
you want your world to be in terms of the unit
system you established in the preparatory step.
You can then use a plane primitive as the starting
point for your terrain. Figure 5 depicts a 1000x1000
unit terrain suitable for modeling a small street,
which has been painted green.
Viewing the Model in the Game Develop-
ment Environment. While a green plane may
seem unconvincing as a terrain, especially when

In polygon modeling, you typically start off by
adding a primitive object like a cube or a plane to
your workspace. Figure 1 depicts both a cube and a
plane. Cubes and planes consist of vertices, edges,
and faces; collectively these are labeled elements .
In addition to cubes and planes, most modeling
programs include spheres, cylinders, and cones as
primitive objects. Given a primitive object, there
are four basic operations or techniques that you
can perform: (1) move one or more elements; (2)
remove one or more elements; (3) cut edges into
faces; or (4) extrude faces.
The move and remove techniques. You can
move or remove any vertex, edge, or face element.
Figure 2 depicts an example of moving each of
these elements. Removing an element from an
object can have unforeseen results. For example,
removing a vertex from a cube also removes the
three faces that the vertex is a part of (not shown).
The cut technique. Moving and removing the
vertices, the edges, and the faces of an object
gives you some variety in creating new objects.
To get more variety, you must cut new edges onto
the object. Figure 3 depicts examples of vertical,
horizontal, and diagonal cuts. Cutting new edges
also creates new faces and vertices. For example,
a vertical cut on a cube face yields two faces and