# 3x3 Matrix for 2D ?

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I was skimming across the internet looking for 2D matrix math examples, when I found Sam's Publishing website... they had something about it on there for some reason. I looked at the tutorial and one thing stuck out to me. Why are they using a 2D vector with components x, y, and w? and why are they using a 3x3? I'm also curious as to what w ever did in the first place...

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The short version: w is used in homogenous coordinate systems. Basically, it distinguishes between point vectors and direction/magnitude vectors; points having a w of 1 and direction/magnitude have a w of 0. This allows transformations to be applied in a uniform manner to both types of vectors.

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If you are curious and know some linear algebra you may want to look up "projective geometry" on the internet, to see where the theory comes from. It's also a lot easier to visualise homogeneous coordinates in 2d (projected on the surface of a 3d hemisphere) than in 3d (projected onto a 4d hyperspehere).

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Thanks SiCrane.

I'm still curious however, where can I find tutorials or referances of 2D Matrix maths. I'm implementing my own math system, no questions. Its a learning experience. I'm going to be using it for transforming shapes (arrays of points). Anyone have a nice site?

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