In mathematics, a geometric transformation is any bijection of a set to itself (or to another such set) with some salient geometrical underpinning. More specifically, it is a function whose domain and range are sets of points — most often both or both — such that the function is bijective so that its inverse exists.^{[1]} The study of geometry may be approached by the study of these transformations.^{[2]}
Geometric transformations can be classified by the dimension of their operand sets (thus distinguishing between, say, planar transformations and spatial transformations). They can also be classified according to the properties they preserve:
Each of these classes contains the previous one.^{[8]}
Transformations of the same type form groups that may be sub-groups of other transformation groups.
Many geometric transformations are expressed with linear algebra. The bijective linear transformations are elements of a general linear group. The linear transformation A is non-singular. For a row vector v, the matrix product vA gives another row vector w = vA.
The transpose of a row vector v is a column vector v^{T}, and the transpose of the above equality is Here A^{T} provides a left action on column vectors.
In transformation geometry there are compositions AB. Starting with a row vector v, the right action of the composed transformation is w = vAB. After transposition,
Thus for AB the associated left group action is In the study of opposite groups, the distinction is made between opposite group actions because commutative groups are the only groups for which these opposites are equal.