Transformations are not only used to rotate, scale or skew a coordinate system. They are also used to completely transform a coordinate system into a totally different coordinate system. For example, transforming a 3D coordinate system into a 2D coordinate system.

The coordinate system of a character gets transformed multiple times as it passes through the OpenGL pipeline. The character starts off in what is know as the **Model** coordinate system. It then gets transformed into the **World** coordinate system, then to a **Camera** coordinate system and finally into a **Projection** coordinate system.

### Model Coordinate System

The **Model Coordinate System** is simply the coordinate system where the character was created.

### World Coordinate System

A Model Coordinate System is the unique coordinate space of the model. Two distinct models, each with their own coordinate systems can’t interact with each other. There needs to be a universal coordinate system that allows each model to interact with each other. This universal system is called **World Coordinate System**. For interaction to occur, the coordinate system of each model is transformed into the World Coordinate System.

### Camera Coordinate System

What is seen on a screen, is relative to a viewer. More specifically to a camera. A change in a camera’s orientation and position changes what a viewer sees. A *World Coordinate System* is transformed into a coordinate system called **Camera Coordinate System**. This coordinate space defines what it is seen on a screen.

### Projective Coordinate System

What is perceived in a screen as three dimensional is just an illusion. It is just a two dimensional image. The final transformation in the OpenGL pipeline occurs in what is called the *Projective Coordinate System*. This transformation converts a three dimensional scenery into a two dimensional image. The Projective coordinate system can be configured in two ways:
- Perspective View
- Orthogonal View

#### Perspective View

When the projective's coordinate system is set as a *Perspective View,* it gives the illusion of producing a three dimensional scenery. This is an illusion created by producing a vanishing point and making objects farther from the camera smaller, thus producing the illusion of depth.

#### Orthogonal View

In *Orthogonal View*, every object in the scene is seen as a two-dimensional objects. There is no illusion of depth.