文章來源：
http://www.codeproject.com/Articles/42086/Space-and-Matrix-Transformations-Building-a-3D-Eng
小結：
projection transform 投影變換
diagonal 對角線
quaternion 四元數
transpose matrix 轉置矩陣
identity matrix 單位矩陣
Local transform 局部轉換
cross product 叉積，向量積
dot product 點積，標量積，數量積
perspective transform 透視變換
OpenGL 使用的是右手座標系統。
The World Space Transform is the first transform usually applied to a model.
This transform is normally used to scale and orient the model relative to its world.
The Model is defined in a model space coordinate system and needs to be translated
to the world coordinate system.
通常，模型面對的第一個變換就是世界空間變換，這種變換通常用來對模型進行縮放以適應模型展現，
被定義在模型座標系統中的模型需要將其轉變成世界座標系。
After a model is transformed to its position into World Space it will then be
transformed in to View Space or Camera Space.
模型被轉變成世界座標系以後，接着才能被轉變成視口空間或攝像機空間
Perspective Transform[透視變換]
After a model is transformed to its position into View Space, it will then be transformed
in to its final viewed position via projection transformation. There are two basic types
of projection transforms that I am aware of: Orthographic, and Perspective. The Perspective
projection mimics the way we perceive the real world. Objects that are closer appear larger
and parallel lines converage at the horizon. Here is how the Perspective transform is constructed.
當一個模型被變換到視口空間之後，然後需要通過透視變換來獲取最終的視圖位置，這裏有兩種基本的投影變換:
正交投影 和 透視投影，透視投影模擬我們所感知的真實世界，對象更接近說看到的，