eriktim / qgsaffine

Perform Affine transformations (translation, rotation, scale) on vector geometries.

qgsAffine: Affine Transformations

Apply affine transformations to selected geometries.

This Quantim GIS (QGIS) plugin performs affine transformations on layers or a group of features.

Concept

For those infamiliar with affine transformations, here is the basic concept.

A point (x,y) can be tranformed to a new point (x',y') by:

x' = a * x + b * y + tx
y' = c * x + d * y + ty

where tx and ty are the translations in the x- and y-direction, resp.
a, b, c and d form the transformation matrix

    | a  b |
A = |      |
    | c  d |

that determines the rotation and scaling.

a, b, c, d, tx and ty are the variablesthat can be changed in the plugin.
Details on how to find the correct values for your case can be found anywhere on the Internet.

Defaults

By default, the translations are zero and T = I (the identity matrix), i.e.

x' = 1 * x + 0 * y + 0 = x
y' = 0 * x + 1 * y + 0 = y