Affine Transform Object

Container for accumulating 2D affine transformations. Simple spatial transforms (spatShift(), spin(), rescale(), flip(), t(), shear()) can be chained on an affine2d to build up a combined transform, which is then applied to spatial objects in a single step via affine().

Create an identity affine2d with affine() (no arguments). Before chaining centroid-relative operations (spin(), rescale()) without explicit x0/y0, set ext(aff) <- ext(your_object) so the pivot point matches your data.

The combined linear transform is stored as a 3x3 homogeneous matrix in @affine. Translations are encoded in column 3 (rows 1-2). The convention is post-multiply: xy_out = xy_in %*% A.

Slots

anchor

numeric(4). Anchoring spatial extent (xmin, xmax, ymin, ymax). Set via ext(aff) <- to match the data extent. Used as the centroid pivot for spin() and rescale() when x0/y0 are not supplied, and for translation calculation during transform composition.

affine

matrix. 3x3 homogeneous transform matrix encoding the combined linear + translation transform.

order

character. Records the order in which component operations were applied.

rotate

numeric(1). Accumulated rotation angle in radians.

shear

numeric(2). Accumulated shear factors (x, y).

scale

numeric(2). Accumulated scale factors (x, y).

translate

numeric(2). Accumulated translation (x, y).