nrrd.vox2ras: Compute the voxel-to-RAS matrix of a NRRD volume.

In freesurferformats: Read and Write 'FreeSurfer' Neuroimaging File Formats

Compute the voxel-to-RAS matrix of a NRRD volume.

Description

NRRD stores the geometry of a volume as one direction vector per space axis ('space directions'), the world position of the center of voxel (0,0,0) ('space origin') and the world space these refer to ('space'). Voxel indices are 0-based. The matrix returned here always maps to RAS+ coordinates (x = right, y = anterior, z = superior), which is the space used by FreeSurfer, by the NIfTI standard and by the rest of this package: a file that states the LPS space therefore has the sign of its first two axes flipped.

Usage

nrrd.vox2ras(fields, dimension, filepath = "")

Arguments

fields	named list, the parsed header fields.
dimension	integer, the number of dimensions of the volume.
filepath	character string, path to the file, used in warnings.

Value

named list with entries matrix (the 4x4 voxel-to-RAS matrix, or NULL when the file carries no space information at all) and source (character string, how the matrix was derived: 'space directions', 'spacings' or NULL).

freesurferformats documentation built on Sept. 25, 2026, 1:07 a.m.