Environment Mapping

Environment mapping is a technique for approximating the reflective surface of an object using its surrounding environment. According to [6], in its most basic form, The technique gives rendered objects a “chrome-like appearance”. An example of this is Robert Abel and Associates’ “Sexy Robot” animation.

Assumptions:

Before going any further, the reader must first learn key assumptions in using this technique:

  1. The environment in relation to the object must be of an infinite distance. Due to its ‘approximating’ nature, the result of the reflection may not appear physically accurate in terms of the distance of the object and the environment. As a consequence, nearby objects may appear in the wrong place on the reflection. [6]
  2. It works most effectively on convex objects because environment mapping is not self-reflective. Furthermore, do not expect multiple reflection to occur in objects that possess reflective property. [6]

The advantage of this technique is its superiority in speed of rendering in comparison to ray tracing(a technique that captures multiple levels of reflection and refraction), a more versatile and comprehensive technique. Which is why it could be thought of as a ‘poor man’s’ ray tracing due to its relatively low cost of computational expense [9].

The disadvantage however is its inaccuracy of mapping the position of the environment relative to the object. Furthermore, each object will need to have its own environment map and the quality of the reflection relies on the quality of the environment map being used. Lastly, this technique does not produce self-reflection.

There are several ways of capturing the environment around the object. This is  list of the most commonly used techniques:

  1.  Sphere mapping
  2.  Cube mapping
  3.  Paraboloid mapping

Sphere Mapping

Sphere mapping is a technique where the environment itself is defined on a sphere[11][12]. Take a look at figure 17

Figure 16: Using sphere mapping technique to mimic an object's room reflection.

Cube Mapping

Figure 16: The Cube Map being flattened to see the cube's different faces. Image taken from Codemonsters: http://www.codemonsters.de/home/img/textures/orientation_convention.png

Cube mapping uses six independent images viewed from the cube’s center to give the projection of the environment. The topology of this cube is displayed in Figure 16.  [9]

Paraboloid Mapping

Paraboloid mapping, is similar to that of the sphere mapping however it uses two paraboloid rather than one [13]

 Next OpenGL Implementation…

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  • Declarion of own work

    I declare that this work is my own Author Roldan Fritz Tagaro, contact me for more information at: acb08rt@shef.ac.uk
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