quaternToMatrix: Convert Quaternion Parameters to a Transformation Matrix

In bbuchsbaum/neuroim2: Data Structures for Brain Imaging Data

Convert Quaternion Parameters to a Transformation Matrix

Description

Given a quaternion (b, c, d), a scalar offset (origin), voxel step sizes, and the qfac sign, reconstructs a 4x4 affine matrix representing rotation, scaling, and translation as used in NIfTI-1.

Usage

quaternToMatrix(quat, origin, stepSize, qfac)

Arguments

quat	A numeric vector of length 3 containing the quaternion parameters (b, c, d). The scalar part a is computed internally.
origin	A numeric vector of length 3 specifying the translation components (often the real-space origin or offset).
stepSize	A numeric vector of length 3 giving the voxel dimensions along each axis (e.g., (dx, dy, dz)).
qfac	Either +1 or -1, indicating the sign from the determinant check in matrixToQuatern.

Details

This function uses the quaternion formalism common in neuroimaging, adding the offset (translation) into the 4th column, and applying the voxel sizes along each axis. If qfac is -1, the z scale is negated. The resulting 4x4 matrix is typically used as an affine transform for voxel-to-world coordinate mapping.

Value

A 4x4 numeric affine transformation matrix. The top-left 3x3 submatrix encodes rotation and scaling, and the 4th column encodes translation.

See Also

matrixToQuatern for converting a matrix back to quaternion form.

bbuchsbaum/neuroim2 documentation built on Feb. 26, 2025, 3:49 p.m.