isAffine: Create, test for and print affine matrices

Description

isAffine returns a logical value indicating whether its argument is, or resembles, a 4x4 affine matrix. asAffine converts other objects to the affine class, attaching or updating the source and target image attributes. Affine transformations are a class of linear transformations which preserve points, straight lines and planes, and may consist of a combination of rotation, translation, scale and skew operations.

Usage

isAffine(object, strict = FALSE)
asAffine(object, source = NULL, target = NULL, ...)
# S3 method for niftyreg
asAffine(object, source = NULL, target = NULL, i = 1L,
  ...)
# S3 method for niftyregRDS
asAffine(object, source = NULL, target = NULL, ...)
# S3 method for affine
asAffine(object, source = NULL, target = NULL, ...)
# S3 method for niftiImage
asAffine(object, source = attr(object, "source"),
  target = attr(object, "target"), ...)
# S3 method for default
asAffine(object, source = NULL, target = NULL, ...)
# S3 method for affine
print(x, ...)

Value

For isAffine, a logical value, which is TRUE if

object appears to be an affine matrix. For asAffine, a classed affine object with source and target attributes set appropriately.

Arguments

object: An R object.
strict: If TRUE, this function just tests whether the object is of class "affine". Otherwise it also tests for an affine-like 4x4 matrix.
source, target: New source and target images for the transformation.
...: Additional parameters to methods.
i: The transformation number, for niftyreg objects containing more than one.
x: An "affine" object.

Author

Jon Clayden <code@clayden.org>

Details

NiftyReg's convention is for affine matrices to transform world coordinates (in the sense of voxelToWorld) from TARGET to SOURCE space, although transforms are logically applied the other way.