Translation;
rotation;
and scale.
Affine transformation can do translations, and rotations, and scales simultaneously:
x' = A x + B y + C
y' = D x + E y + F
Affine transformations generalize translations, rotations, and scales. A translation is:
x' = x + C (A = 1, B = 0)
y' = y + F (D = 0, E = 1)
A rotation is:
x' = sin(r) x + cos(r) y (A = sin(r), B = cos(r), C = 0)
y' = cos(r) x - sin(r) y (D = cos(r), E = -sin(r), F = 0)
And a scale is:
x' = A x (B = 0, C = 0)
y' = E y (D = 0, F = 0)
They are all special cases of affine transformations.
One way to generalize affine transformation would be to introduce a divisor:
x' = | A x + B y + C |
a x + b y + c |
y' = | D x + E y + F |
a x + b y + c |
But! There is another!
x' = A x + B y + C + D x y
y' = E x + F y + G + H x y
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